C1 Species and Communities

• Survival factors

  • U: The distribution of species is affected by limiting factors

    • Limiting factor = a component of an ecosystem which limits the distribution or numbers of a population

      • Defines optimal survival conditions according to its effect on a species when in deficiency or excess

      • Can be biotic or abiotic

        • Biotic factors include interactions between organisms

          • Either intraspecific (within a species)

          • Or interspecific (between species)

        • Abiotic factors include environmental conditions

          • E.g. light, temperature, salinity (concentration of salts in water or soils), rainfall, wind velocity, soil pH, etc.

      • Typical abiotic limiting factors for plants within a community

        • Temperature

          • Plants can only survive within a narrow range of temperatures to which they are adapted

          • High temperatures will increase the rate of water loss by evaporation and may also denature metabolic enzymes

          • Low temps may cause plant sap to freeze

            • The expansion of frozen water in xylem can cause trunks to split

          • Certain species of woody plants synthesis antifreeze protein to prevent crystal formation in frozen cells

            • E.g. maple trees

        • Water availability

          • Water is needed for photosynthetic processes + maintaining cell turgor

          • Xerophytes are plant species that are adapted to survive in dry and arid environments such as deserts

            • E.g. cacti

          • Hydrophytes are plant species that are adapted to survive in frequently waterlogged soils

            • E.g. rice

        • Light availability

          • Light is essential to the process of photosynthesis whereby plants produce organic molecules

          • Low-growing plants will typically possess darker leaves in order to optimize their light conversion

            • Dark = more chlorophyll

          • Certain seaweeds have pigments adapted to absorbing blue wavelengths

            • E.g. kelp

            • Red does not easily penetrate water

      • Typical abiotic limiting factors for animal within a community

        • Temperature

          • Animal survival typically relies on narrow temperature range

            • Few animals can survive temperature extremes

          • Poikilotherms cannot maintain thermal homeostasis and must occupy environments according to temperature needs

          • Homeotherms can regulate their own internal body temperatures and hence can occupy a wider range of habitats

          • Body size will play a fundamental role in determining an animal’s capacity to retain heat

            • The surface area to volume ratio

        • Territory

          • Territorial boundaries may determine an animal's capacity to attract mates, rear young, forage for food and avoid predators

          • Territories may be temporary (e.g. migration, breeding sites) or alternatively may be permanent

          • In certain species, juveniles may have different environmental requirements to adults

            • E.g. tadpoles and frogs

          • Establishment of territories can lead to intraspecific and interspecific competition

        • Food availability

          • Availability of food supply is a critical determinant in influencing population size and distribution

          • Animals may require a particular plant or animal species as a food source

            • This limits their spread to certain regions

            • Seasonal or geographic variations may directly affect food availability within a population

              • E.g. seasonal migrations

    • Law of Tolerance

      • The Law of Tolerance was proposed by Victor Ernest Shelford (American zoologist) in 1911

      • States that populations have optimal survival conditions within critical minimal and maximal thresholds

        • When populations are exposed to the extremes of a particular limiting factor (too much or too little), the survival rates drop

      • The distribution of species in response to a limiting factor is a bell-shaped curve with 3 distinct regions

        • The optimal zone

          • Central portion of a curve which has conditions that favor maximal reproductive success and survivability

        • Zones of stress

          • Regions flanking the optimal zone where organisms can survive but with reduced reproductive success

        • Zones of intolerance

          • Outermost regions in which organisms cannot survive

          • Represents the extremes of the limiting factor

        • Example:

        • 

  • A: Distribution of one animal and one plant species to illustrate limits to tolerance and zones of stress

    • Plant example

      • Plant growth varies greatly in response to salinity levels (concentrations of salt within the soil)

      • Plants that are not salt tolerant are called glycophytes

        • They are easily damaged by high salinity

        • Most plant species are considered glycophytes

      • Plants that are salt tolerant are called halophytes

        • They may become stressed in freshwater environments

        • Less than 2% of all plants are halophytes

      • Cultivation of land for agriculture causes the water table to rise and concentrates salt at the roots

        • Such cultivation includes irrigation and grazing

        • This makes it harder for glycophytes to extract water from the soil and the uptake of salt can be toxic to the plant

      • Understanding salt tolerance for different plant species is therefore critically important to effective crop farming

    • Animal example

      • Coral species form connected reefs → these are greatly impacted by changes in oceanic temperature

      • Coral polyps receive nutrition from photosynthetic zooxanthellae that lives within the polyp’s endodermis

        • Zooxanthellae = an algae

        • Endodermis = an inner layer of cells in the cortex of the root

      • The Zooxanthellae cannot survive in lower ocean temperatures

        • Below 18 degrees Celsius

      • Increases in ocean temperature cause Zooxanthellae to leave the coral tissue → this leads to coral bleaching

        • Above 35 degrees Celsius

      • Reef-building coral species therefore have a typical optimal growth range in temperate waters between 20 and 30 degrees Celsius

        • This correlates to the tropical and sub-tropical regions of the world (near the equator)

• Species distribution

  • S: Use of a transect to correlate the distribution of plant or animal species with an abiotic variable

    • Quadrats and transects can measure the distribution of a plant or animal species in response to an incremental abiotic factor

      • Incremental = happening gradually

      • Quadrats = rectangular frames of known dimensions than can be used to establish population densities

      • Transects = a straight line along an abiotic gradient from which population data can be recorded to determine a pattern

      • Quadrats and transects are used together

    • Quadrats are placed at regular intervals along the transect line to generate population data

      • Basically, placing a quadrat down regularly and observing/counting the difference in distribution of X species based on the change of Y abiotic variable

      • The quadrats will show the changing distribution pattern of a species in response to a change in an abiotic variable

      • This data can be used to identify optimal conditions + zones of stress and zones of tolerance

    • Sampling with Quadrats and Transects

      • Quadrat counting method: count all variables mostly inside the quadrat (not mostly out)

      • Line transects: find a line, place quadrat every x meters

      • Transect data

        • Transects are used to assess species distribution in correlation with any abiotic factor that varies across a measurable distance

          • These factors could include elevation, elemental exposure, temperature, light levels, pH, humidity and more

      • A kite graph with the transect data can be used to represent changes in species distribution in a clear and effective fashion

        • The relative width of each kite represents the abundance of an organism at a particular point along a transect

        • Example:

• Ecological niche

  • U: Each species plays a unique role within a community because of the unique combination of its spatial habitat and interactions with other species

    • Ecological niche = the functional position and role of an organism within its environment

      • Consists of all physical and biological conditions which determine the organism’s survival and reproductive prospects

      • Is comprised of various components, including:

        • The habitat in which an organism lives

        • The activity patterns of the organism

          • E.g. periods of time during which it is active

        • The resources it obtains from the environment

          • E.g. food sources, territorial boundaries, etc.

        • The interactions that occur with other species in the community

          • E.g. predator prey relationships, competition, etc.

  • U: Two species cannot survive indefinitely in the same habitat if their niches are identical

    • If two distinct species share an identical niche, there will be interspecific competition for available space and resources

      • This competition will result in the fitness of one being lowered by the presence of the other

      • The less well-adapted species will struggle to survive and reproduce

        • Eventually it will be eliminated from the niche

    • Interspecific competition within a shared niche will typically prompt one of two responses

      • Competitive exclusion → one species uses the resources more efficiently, driving the other species to local extinction

      • Resource partitioning → both species alter their use of the habitat to divide resources between them

        • Niche separation

    • Niche differentiation diagram:

  • S: Analysis of a data set that illustrates the distinction between fundamental and realized niche

    • Some species may not be able to occupy their entire niche due to the presence or absence of other species

      • Hence, a species may occupy a small subset of their niche than is theoretically possible

      • This creates fundamental vs. realized niche

    • Fundamental niche = the entire set of conditions under which an organism can survive and reproduce (where it could live)

      • The theoretical habitat

      • Example: in a rocky shore environment, the Chtalamus barnacle can potentially occupy the entire rocky shore, if in isolation

    • Realized niche = the set of conditions used by an organism after including interactions with other species (where it does live)

      • The actual habitat that is completely occupied by an organism in the presence of competing species

      • Example: the Chtalamus barnacle only occupies regions where the Semibalanus barnacle is absent

    • Diagrams:

      • Niches

      • Experimental data

      • Types of barnacles

• Species interactions

  • U: Interactions between species in a community can be classified according to their effect

    • In nature, no species exist in total isolation → all organisms interact with both the abiotic environment and other organisms

      • The interactions between species can be classified according to their effect on the organisms involved

    • Herbivory

      • The act of eating only plant matter

        • That’s why primary consumers are called herbivores

        • Herbivores ay employ different feeding strategies

          • E.g. mucivores feed on plant sap while granivores feed on seeds, etc.

      • Herbivory can be either harmful or beneficial to plant species as a whole

        • Harmful: Certain types of beetle may feed voraciously on the leaves which causes crop failure

        • Beneficial: Fruit-eating animals spread the seeds from a fruit in their feces, which promotes overall seed dispersal

      • Examples of herbivores: Rabbit, cow

    • Predation

      • A biological interaction whereby one organism hunts and feeds on another organism

        • Predator and prey

      • The dependance of the predator on the prey as a food source intertwines their population levels

        • If the prey population drops, the predator numbers will fall as well as intraspecific competition has to increase

        • If the prey population rises, predator numbers will increase as a result of the ober-abundance of a food source

          • No intraspecific competition necessary = even the weakest survives

      • Diagram:

    • Symbiosis

      • Close and persistent long-term interaction between two species

        • Can be obligate (required for survival)

        • Or facultative (advantageous without being strictly necessary)

      • Symbiotic relationships can be beneficial to either one or both organisms in the partnership

        • Mutualism – both species benefit from the interaction

          • Example: how anemone protects clownfish and clownfish provides fecal matter for food

        • Commensalism – one species benefits, the other is unaffected

          • Example: barnacles are transported to plankton-rich waters by whales

        • Parasitism – one species benefits to the detriment of the other species

          • Example: ticks or fleas feed on the blood of their canine host

        • Diagram:

  • A: Local examples to illustrate the range of ways in which species can interact within a community

    • Mutualism

      • Ongoing interaction between two species whereby both species benefit from the interaction

      • Examples:

        • Honey bees gather nectar from flowers and distributes pollen between plants

          • This mediates the plant life cycle

        • Plover birds pick food morsels from between the jaws of crocodiles, cleaning their teeth in the process

        • Zooxanthellae photosynthesise within the protective environment of the polyp’s endodermis

          • This feeds the coral

    • Commensalism

      • Ongoing interaction between two species whereby one benefits and the other is unaffected

      • Examples:

        • Remora attaches to the underside of larger predatory fish and feed off the uneaten food scraps

        • Monarch butterflies can safely store poisonous chemical produced by milkweeds discourage predators from eating it

        • Decorator crabs remove small fragments of tissue from sea sponges and uses them as a source of camouflage

    • Parasitism

      • Ongoing interaction between two species whereby one species benefits at the other’s expense

      • Examples:

        • Ticks infest the skin and fur of host animals, feeding off the host and potentially causing disease

        • Leeches attach to the skin and drinks the blood of the host animal until fully engorged

        • Tongue-eating louses eat the tongue of a fish and may still later ingested food

  • A: The symbiotic relationship between Zooxanthellae and reef-building coral reef species

    • Reef-building coral will form a mutualistic symbiotic relationship with the photosynthetic unicellular algae Zooxanthellae

      • Coral are colonial organisms made up of individual polyps that are connected by a layer of living tissue

      • The algae lives within the cells of the coral’s endodermis (the innermost lining of the animal)

    • The coral provides the algae with a protective environment and source of inorganic compounds

      • Coral polyps secrete calcium carbonate to build a stony skeleton which encases the polyps and the Zooxanthellae

      • Coral polyps also recycle the waste products of the algae and supplies the Zooxanthellae with CO2

    • The Zooxanthellae in turn provides the coral polyps with a necessary source of nutrition

      • The alage supplies the coral with oxygen, glucose and other organic molecules that it produces via photosynthesis

      • The algae also helps the coral remove necessary waste products

    • Diagram of their mutualistic relationship:

    • Coral bleaching

      • It is the Zooxanthellae that gives the coral its vibrant pigmentation

      • When there is a large scale loss of Zooxanthellae from the coral due to environmental stress, bleaching of the coral occurs

        • This causes the coral to starve and die unless the Zooxanthellae are restored

      • Conditions which can cause coral bleaching include:

        • Changes in light availability

          • E.g. sedimentation may increase the opacity of the oceanic waters

        • Temperature increases

          • Water temperatures in excess of 30 degrees Celsius can irrevocably stress the Zooxanthellae

        • Ocean acidification

          • The buildup of CO2 concentrations in the ocean can lower pH and stress the Zooxanthellae

• Keystone species

  • U: Community structure can be strongly affected by keystone species

    • Keystone species = a species that has a disproportionately large impact on the environment relative to its abundance

      • Name comes from the keystone in an arch → it fundamentally supports the whole structure and prevents it from collapsing

    • Keystone species may influence communities in a number of ways:

      • Predators can exert pressure on lower trophic levels to prevent them from monopolizing certain resources

      • Mutualists can support the life cycle of a variety of species within a community

        • E.g. pollinators and seed dispersal

      • Engineers can refashion the environment in a manner that promotes the survival of other species

        • Engineer = any species that creates, significantly modifies, maintains and/or destroys habitats

    • Numerous examples of keystone species within different communities, such as:

      • Sea stars (predators) prey on urchins and mussels, which prevents mussel overpopulation and coral reef destructions by urchins

      • Honey bees (mutualist) pollinate a wide variety of plant species, ensuring the continuation of the plant life cycle

      • Beavers (engineer) build dams that transform the environment in a manner that allows certain other species to survive

    • Keystone species are not the dominant species (most numerous) within a community nor do they have to be apex predators

    • Diagram of consequences of removal of keystone species:

C2 Communities and ecosystems

• Trophic levels

  • U: Most species occupy different trophic levels in multiple food chains

    • Trophic level = the position an organism occupies within a feeding sequence

      • Producers occupy the first trophic level in a feeding sequence

      • Primary consumers feed on producers → second trophic level

      • Secondary consumers feed on primary → third trophic level

      • Further consumers occupy the subsequent levels

      • Diagram:

    • Food chain = shows linear feeding relationships between species in a community

      • Arrows represent the transfer of energy and matter

        • This transfer happens as one organism is eaten by the other

        • The arrows point in the direction of energy flow

      • Goes from the producer to the consumers

      • Most species’ feeding requirements means they will be in multiple food chains where they may occupy a different trophic level

        • As few species only feed on one other species

      • E.g.:

  • U: A food web shows all the possible food chains in a community

    • Links food chains together into more complex and interrelated feeding relationships

    • More representative of actual feeding pathways within an ecosystem because

      • Organisms can have more than one food source

      • Organisms can have more than one predator

      • Hence, organisms can also occupy more than one trophic level

    • Tip! When constructing food webs, position organisms at their highest trophic level (from left to right) as it keeps all arrows pointing in the same directions

    • Example:

  • EC: Ecological Pyramids

    • Ecological pyramids show the relative amounts of a specific component at the different trophic levels of an ecosystem

      • The three main types measure species numbers, biomasses and energy

    • Pyramid of Numbers

      • Shows the relative number of organisms at each stage of a food chain

      • Are usually shaped like pyramids → higher trophic levels cannot be sustained if there are more predators than prey

        • However, the shape may be distorted if a food source is disproportionately large in size/biomass compared to the feeder

          • E.g. a large number of caterpillars may feed on a single oak tree

    • Pyramid of Biomass

      • Shows the total mass of organisms at each stage of a food chain

      • Almost always upright in shape as biomass diminished along food chains as CO2 and waste is released

        • An exception to this rule is found in marine ecosystems where zooplankton have a larger total biomass than phytoplankton

          • Because phytoplankton replace their biomass at such a rapid rate and can therefore support a larger biomass of zooplankton

    • Pyramid of Energy

      • Shows the amount of energy trapped per area in a given time period at each stage in a food chain

      • Always upright in shape as energy is lost along food chains

        • Either used in respiration or lost as heat

      • Each level in the pyramid is roughly one tenth the size of the preceding level as energy transformations are ca. 10% efficient

    • Examples of pyramids:

• Energy conversions

  • U: The percentage of ingested energy converted to biomass is dependent upon the respiration rate

    • Ecological production/productivity refers to the rate at which biomass is generated in an ecosystem

      • Usually expressed in units of mass per area per time

        • km m^-2 day^-1

    • Biomass = total dry weight of organic matter in organisms or ecosystems

      • The entirety of all biologically produced organic matter

        • E.g. proteins, carbohydrates, etc.

    • The percentage of energy that is converted into biomass is dependent upon a number of factors that lose energy

      • Energy is lost as inedible materials (bones, teeth, hair)

      • Energy is lost via excretion of undigested or unabsorbed materials

      • Energy is lost as heat from cellular respiration

        • The higher respiration rate results in more heat lost

    • Primary production = the production of chemical energy in organic compounds by producers

      • The main source of energy for primary production is sunlight

        • Sometimes chemosynthesis by lithotrophs

      • Can be categorized as one of two types:

        • Gross primary production (GPP) → the amount of chemical energy as biomass that a producer creates in a given length of time

        • Net primary production (NPP) → the amount of chemical energy that is not consumed by respiration

          • GPP - respiration

    • Secondary production ? the generation of biomass by heterotrophic organisms (consumers)

      • Biomass generation is driven by the transfer of organic compounds between trophic levels via feeding

      • Secondary production may also be categorized according to gross and net amounts of biomass

        • Gross = total

        • Net = usable

    • Diagram explaining how ingested energy converted to biomass depends on respiration:

• Feed Conversion Ratio

  • A: Conversion ratio in sustainable food production practices

    • Feed Conversion Ratio (FCR) = mass of feed/mass of desired output

      • FCR measure the efficiency of an animal in converting food into a desired output

      • The lower the FCR the more efficient the method of food production

    • Low FCR is achieved by minimizing the potential losses of energy for the animal stock

      • Restricting animal movement will reduce energy lost to cell respiration

      • Optimizing feeding practices so that food is ingested and digested more effectively

      • Slaughtering animals at a young age

        • As older animals tend to grow more slowly and have a higher FCR

    • Theoretically the most efficient FCR is best as it lowers cost, however there are a number of potential ethical issues involved

      • Is it ethical to restrict animals and kill them early?

    • Diagram displaying the FCRs of different species:

  • EC: Sustainable food practices

    • Most of the protein found in Western human diets comes from farmed animal meet

      • E.g. cattle and poultry

      • These animals must be fed and housed → this creates an ecological footprint, the size of which depends on the FCR

    • Sustainable food practices provide food for the consumer while minimizing the environmental impact of the food source

      • The benefits of lowering food production costs must be balanced against ethical considerations regarding animal treatment

    • One sustainable food practice is the use of crickets as a protein source (as opposed to cattle)

      • Crickets have a substantially lower FCR → minimizes feed costs

      • They require significantly less water → minimizes water usage

      • They can reproduce much faster and require less space

      • Produce far less methane

      • For these reasons, certain health professionals are advocating the introduction of crickets into normal diets

        • The advantages of crickets as a food source is still debated though, so implementation is likely to be slow

• Types of Ecosystems

  • U: In closed ecosystems energy but not matter is exchanged the with the surroundings

    • Ecosystems can either be open or closed, depending on whether matter moves into and out of the system

      • A closed ecosystems exchanges energy with its surrounding, but not matters

        • It is self-contained

        • E.g. a mesocosm

      • An open ecosystem changes both energy and matter with surrounding environments

        • A natural ecosystem such as a forest

  • U: The type of stable ecosystem that will emerge in an area is predictable based on climate

    • Ecosystem = the interaction of living and non-living things within an area

      • A community and its abiotic environment

    • Particular types of stable ecosystems will emerge in a given geographical area according to its climate conditions

    • Biome = a geographical area that has a particular climate and sustains a specific community of plants and animals

      • Basically a specific type of natural ecosystem, created from its climate and environment

      • The main factors affecting the distribution of biomes is temperature and rainfall

      • These factors vary according to latitude, longitude, altitude, proximity to ocean, etc.

    • Many different biomes are found across continents, including:

      • Tropical rainforests

        • Hot and humid environments

        • Near the equator

        • Dense vegetation

        • High biodiversity

      • Taiga

        • Coniferous forests

        • Near the poles

        • Have cold temperatures

        • Little precipitation

          • Moisture trapped as snow or ice

      • Deserts

        • Dry and arid environments

        • Display extreme temperature conditions (hot and cold)

      • Picture examples:

  • EC: Types of Biomes

    • Biomes are geographical area that have a particular climate and sustain a specific community of flora and fauna

      • The total area where all living things are found is called the biosphere

        • The totality of biomes

      • Certain biomes are named and recognized according to their specific characteristics

    • Tropical rainforest

      • Hot climate → 25-30 degrees Celsius

      • Very high levels of precipitation → > 250 cm per year

      • Large diversity in species

      • Vegetation includes epiphytes, tall trees and undergrowth

        • Epiphytes: organisms that grow on the surface of plants

    • Temperate forest

      • Also called deciduous forests

      • Moderate temperatures and clear seasonal changes

      • Growing period of around 200 days during 4-6 frost free months

    • Boreal forest (Taiga)

      • Coniferous forests

      • Cold and icy → 0-15 degrees Celsius

      • Only small amount of precipitation

      • Coniferous trees are densely packed and there is little variation in species

    • Tropical Grassland (Savannah)

      • Warm → 20-30 degrees Celsius

      • Medium amounts of moisture, although seasonal droughts are common

      • Trees are intermittent and widely spaced

      • Occasional fires prevents thicker vegetation from encroaching

    • Temperate Grassland

      • Moderate temperatures and amounts of rainfall

      • Trees and shrubs are largely absent

      • Grass is the dominant vegetation

    • Mediterranean (Chaparral)

      • Moderate temperatures → 15-25 degrees Celsius

      • Rainy winters and dry summers

      • Vegetation consists of dry woody shrubs that are quick to grow

    • Desert

      • Extreme temperature conditions → > 30 degrees Celsius during the day, < 0 degrees at night)

      • Very low precipitation

        • < 30 cm per year

      • Dominant plant species are xerophytes which are adapted for water conservation

    • Tundra

      • Freezing temperatures → < 0 degrees Celsius

      • Very little precipitation

      • Vegetation is low growing

        • E.g. mosses

      • Perennial plants may grow during the summer

    • Mountain ranges

      • Found all over the world at high attitudes → > 10 000 feet

      • Temperatures are typically low due to the altitude

      • Weather conditions may change rapidly

    • Distribution of biomes in the biosphere:

      • 

• Ecosystem Analysis

  • S: Analysis of a climograph showing the relationship between temperature, rainfall and the type of ecosystem.

    • Climograph = graphical representation of basic climate parameters at a given geographical location

      • Shows a combination of monthly average temperature and precipitation at a certain location

        • Precipitation = rainfall

      • Provides a quick overview of the climate of a region and can be used to identify seasonal patterns and changes

      • Examples:

        • 

    • Whittaker’s climograph

      • In 1975, ecologist Robert Whittaker developed a holistic climograph that allowed for the classifying of 9 distinct biomes

      • Biomes distinguished according to their average yearly temperatures and precipitation

        • Deserts typically have high average temperatures but low precipitation

          • Hot and dry

        • Rainforests typically have high average temperatures and high precipitation

          • Hot and wet

        • Taigas typically have low average temperatures and reasonably low precipitation

          • Cold and icy

      • 

  • S: Comparison of pyramids of energy from different ecosystems

    • Pyramids of energy (PoE) = diagram of the flow of energy between trophic levels

      • Measures in units of energy per area per time

      • Standard units are kJ m^-2 and y^-1

      • Triangular and never inverted as 90% of energy is lost between trophic levels

    • PoEs differ between ecosystems due to the effect of climate on primary productivity

      • Warmer temperatures speed up enzyme reactions required for photosynthesis

      • High precipitation also increases photosynthesis as the photolysis of water is essential for non-cyclic photophosphorylation

      • Higher (optimal) rate of photosynthesis = more energy transferred

    • Tropical rainforests have a high NPP whereas deserts have a low NPP

      • Higher NPP = more energy supplies to consumers hence more trophic levels can exist

      • Tropical rainforests PoE has a wider base and more levels than a desert

    • Types of species within a particular biome may also affect how efficiently energy is transferred between trophic levels

      • Example: Homeotherms will use more energy maintaining a stable body temperature compared to poikilotherms

    • Diagram:

  • S: Construction of Gersmehl diagrams to show the interrelationships between nutrient stores and flows between taiga, desert and tropical rainforest

    • Gersmehl diagrams show the differences in nutrient flow and storage between different types of ecosystems

    • Nutrients are stored in one of three nutrient sinks

      • Biomass → the total mass of living organisms in a given area

        • Mainly plant tissue

      • Litter → any organic matter in and on the soil

        • Includes humus and leaf litter (defoliation)

      • Soil → the top layer of the earth that is composed of disintegrated rock particles

    • Nutrients can be transferred between nutrient sinks and may also be cycled via environmental inputs and outputs

      • Transfer from biomass to litter → fallout

      • Transfer from litter to soil → decay

      • Transfer from soil to biomass → uptake

      • Litter can additional gain nutrients via precipitation and lose nutrients in surface runoff

      • Soil can gain nutrients from the erosion of rocks via weathering and lose via leaching

    • Standard: Gersmehl diagram

    • Comparing Gersmehl diagrams

      • The inter-relationships between nutrient stores and flows will be affected by climatic factors

        • Such as temperature and rainfall

        • Therefore Gersmehl diagrams will differ between biomes

      • Tropical rainforest

        • Most nutrients are stored as biomass

          • Litter is rapidly decomposed and vast roots quickly draw nutrients from soil

        • There is a fast rate of transfer between stores

          • Hot and wet conditions promote precipitation, runoff, weathering and leaching

      • Taiga

        • Most nutrients are stored as litter

          • Low temperatures slow decomposition which delays nutrient transfer to soil and biomass

        • There is little nutrient gain from precipitation or weathering due to low levels of precipitation

          • Cold temperatures produce snow instead

        • There is little nutrient loss via leaching due to low precipitation

          • But surface runoffs may be high at certain times if the snow melts

      • Desert

        • Most nutrients are stored in the soil

          • Few plants exist to store nutrients as biomass nor to produce litter

        • There is little nutrient gain from precipitation and little nutrient loss via runoff → both due to the dry climate

        • The amount of weathering and leaching is insignificant

      • 

• Primary Succession

  • S: Analysis of data showing primary succession

    • Ecological succession = the process by which a sequence of increasingly complex communities develop over time

      • Climax community = when succession has ended and the community has all of its characteristics

    • Primary succession = when communities develop on entirely new land without any established soil

      • May occur at river deltas, glaciers, sand dunes or on exposed rock

      • First organisms to colonize the region are called pioneer species

        • Typically consist of lichen or moss

          • When they die, they decompose which creates the first organic soil capable of sustaining plant growth

    • As plant species colonize a new area, the litter produced by their growth and decomposing remains will cause changes

      • Soil depth will increase because plants add humus to the soil

      • Soil pH will become altered by the additions

      • Soil mineral content will increase and rocks will begin to be broken down by the action of roots

      • The soil will become aerated and water retention increases

        • Drainage is reduced

      • These changes will allow for growth of larger plants, which will reduce erosion through the binding action of their roots

        • Not all plant species will thrive in unison → larger plants will eventually outcompete smaller shade intolerant plants

    • Overview of primary succession:

    • Primary succession data

      • A primary succession sequence can be identified according to the distribution of plants

        • This applies for any location where a new community may emerge from uninhabitable land

        • The regions closer to the site of development will be in the earlier chronological stages of succession

          • E.g. Glacial retreat exposes bare rock for colonization, so regions further from the glacier have had more time to develop life

      • Diagram example:

• Ecological Disturbance

  • U: Disturbance influxes the structure and rate of change within ecosystems

    • Environmental disturbances may cause fluctuations to the structure and rate of change within ecosystems

      • Such disturbances may be natural or artificial (human-induced)

        • E.g. bushfire, earthquake

    • Natural disturbance

      • A natural environmental disturbance may give rise to secondary succession

        • Secondary succession = one ecosystem is replaced by another

        • Occurs when succession starts on existing soil following the upheaval (change) of a pre-existing ecosystem

          • This upheaval results in the removal of existing biota and allows a new ecosystem to develop on the site of the old

        • Because the soil is already developed during secondary succession, dominance is usually achieved by the fastest growing plants

      • The progression of secondary succession can be summarized as follows:

        • An environmental disturbance destroys the pre-existing climax community

        • Grasses and herbaceous plants are the first to grow back as the soil is already present

          • Soil = no pioneer species required

        • Fast growing trees will develop to their fullest while shade tolerant trees will develop in the understory

          • Eventually the fast-growing trees may be overtaken by larger, slower-growing trees as the ecosystem reverts to its prior state

      • Diagram:

  • A: Consideration of one example of how humans interfere in nutrient cycling

    • Deforestation is the permanent destruction of a forest via the removal or clearance of trees

      • Human-induced degradation of forests

      • Driven primarily by a need for timber and cleared land for agricultural purposes

    • Deforestation disturbs the normal nutrient cycling within the region in a number of ways

      • Less trees means there is less evapotranspiration  meaning there is less moisture/precipitation in the air

      • Fewer trees means less litter

        • Due to less defoliation (leaves falling off a plant)

        • This reduces the production of humus, so there will be less nutrients in the soil

      • Rapid loss of nutrients from leaching

      • Less chemical weathering of rock, due to less water in soil

      • The soil will become more acidic and release iron and aluminum to form an infertile ferralitic soil

        • Ferralitic soil = nutrient poor

      • The soil layer will become increasingly thin and eroded

      • The infertile soil will prevent vegetative growth, reducing biodiversity and nutrient cycling

      • Logging operations may also alter the distribution of plant species by removing the canopy and increasing light exposure

        • Canopy = the upper layer of habitat zone, usually formed by mature tree crowns

      • Removal of the canopy also results in an increases loss of nutrients from the soil via runoff

    • The effect of deforestation on nutrient cycling:

  • S: Investigation into the effect of an environmental disturbance on an ecosystem

    • Environmental disturbances are caused by natural or artificial disruptions to a normal ecosystem

      • Examples:

        • Fire breaks in bush lands or regions damaged by bushfires

        • Outer boundaries of population settlements or regions bordering roads

        • Dams and artificial rivers and creeks

          • E.g. irrigation sites

    • The effect of an environmental disturbance on an ecosystem can be measured in a number of ways

      • Population density

        • Using the Lincoln index via the capture-mark-recapture technique

      • Species diversity and richness

        • Using the Simpson’s reciprocal index

      • The presence and distribution of indicator species

        • To measure levels of pollution

      • Canopy coverage and relative light intensity

        • Could measure with a lux meter

      • Biomass

        • Via the average width of tree stems at a specified height

      • Edaphic factors such as soil erosion (via depth), water retention (via drainage), pH and nutrient content

    • Measurements taken from a disturbed area need to be compared against measurements taken from an undisturbed control area

      • This enables the investigator to statistically calculate both the effect and magnitude of the environmental disturbance

C3 Impacts of humans on ecosystems

• Invasive species

  • U: Introduced alien species can escape into local ecosystems and become invasive.

    • The species within any given ecosystem can be broadly described as either endemic or alien

      • Endemic = native species to a defined geographic region

        • E.g. koalas in Australia

      • Alien = species that have been transferred from their natural habitat into a new environment

      • If an introduced alien species has detrimental effects on the pre-existing food chains, it is classified as invasive

        • Invasive species typically threaten the biodiversity of the ecosystem they are introduced into by displacing native species

    • Example: invasive species in Australia → cane toad, European rabbit, red fox, camel, feral cat

  • U: Competitive exclusion and the absence of predators can lead to reduction in the number of endemic species when alien species become invasive

    • Competitive exclusion principle = two species cannot occupy identical niches within a community

      • One species will have a competitive advantage and survive at the expense of the other

      • Evolution via natural selection results in adaptations that function to minimize direct competition between species in nature

    • Invasive species possess several advantages that allow them to displace endemic species via competitive exclusion:

      • Typically possess a large fundamental niche

        • = can occupy a wider area than endemic species

      • Commonly lack a predator capable of limiting their survival

        • As they are introduced into a foreign environment

      • May possess certain features that are suited to the new environment

        • E.g. more aggression, better foraging, etc.

    • Diagram:

  • A: Study of the introduction of cane toads in Australia and another local example of an introduced alien species

    • Case study one: Cane toads (Bufo marinus)

      • Cane toad was introduced in Australia in 1935 by humans to control the spread of the sugar cane beetle that was damaging crops

        • Failed to limit the beetle population → beetles live at the tops of sugar canes where the toads could not reach

      • The cane toad has reproduced rapidly and is now classified as an invasive species that endangers native wildlife

        • It has a wide diet → depleted the prey population for native insectivores

        • Secretes a toxic chemical from its skin that has poisoned native predators

        • Carries diseases that have been transmitted to native species of frogs and fish

      • The cane toad has spread across the northern fringes of Australia

        • Now numbers in the millions

      • Proven difficult to eradicate as there are no natural predators in Australia to reduce its population size

    • Case study 2: Wild rabbits

      • European rabbits were introduced in Australia with the arrival of the First Fleet

        • Ostensibly for recreational hunting

      • Australian conditions promoted a population explosion

        • Mild winters allowed rabbits to breed the entire year

        • Fastest spread ever recorded for any mammal anywhere in the world

      • Rabbits have had a devastating effect on native Australian ecology

        • Killed native plant species by ringbarking

          • Ringbarking = removing a strip of bark that prevents future growth beyond that point

        • Loss of native plants has left the topsoil exposed and vulnerable to extensive erosion from wind and rain

      • Various strategies have been employed to control rabbit populations with varying effect

        • ‘Rabbit-proof’ fences were built to try and contain rabbit populations

        • Methods of hunting and poisoning have been utilized

          • Also efforts to destroy rabbit warrens (burrows)

        • Rabbit-borne diseases have been released with moderate success

          • E.g. myxomatosis virus

• Biological control

  • S: Evaluation of eradication programmes and biological control as measures to reduce impact of alien species.

    • Controlling the population of invasive species once they have become established is difficult and typically very expensive

      • Three main methods: physical, chemical, biological

    • Physical control

      • Involves removal or restriction by manual or mechanical measures

      • May include:

        • Installation of barriers and fences

        • Removal of habitat by excavation or trimming

        • Population numbers may be reduced by hunting, trapping and culling

          • Although this is labor intensive

      • Physical methods to contain invasive species are not usually species specific and can also impede endemic wildlife

    • Chemical control

      • Involves the use of chemical agents to limit population numbers and spread

        • Chemical agents = poisons and toxins

      • Chemical agents may include:

        • Herbicides for plants

        • Pesticides for insects

        • Other compounds such as rat poison

      • Chemical agents may have moderate specificity, but can also detrimentally affect local wildlife + are costly

      • The effect may become more pronounced in high trophic levels due to biomagnification

    • Biological control

      • Involves using living organisms or viruses to control an invasive species

      • Biological control may eat the invasive species or cause it to become diseased

      • Biological agents mut be carefully assessed before release to ensure they do not become invasive themselves

      • Examples:

        • The Vedalia beetle feeds on citrus plant invertebrates

        • The Myxoma virus that affects rabbits

      • Biological control agents must be monitored for unintended side effects

        • E.g. development of immunity in invasive species

      • Biocontrol case study: The Vedalia Beetle (ladybug)

        • The cottony cushion scale is an invertebrate pest from Australia that was accidentally released in California

          • Spread and fed on citrus plants such as orange trees

          • Devastated the Californian citrus industry

        • The Vedalia beetle is a predatory insect from Australia that was introduced into California as a means of biological control

          • It worked to limit the numbers of the cottony cushion scale

          • Minimized the economic impact on the citrus industry

        • Diagram:

• Biomagnification

  • U: Pollutants become concentrated in the tissues of organisms at higher trophic levels by biomagnification

    • Biomagnification = the process in which chemical substances become more concentrated at each trophic level

      • Bioaccumulation = the build up of a chemical substance in the tissues of a single organism

    • Biomagnification occurs because organisms at higher trophic levels must consume more biomasse to meet feeding requirements

      • Energy transformations are only ca. 10% efficient, so higher order consumers must eat more to meet energy demands

      • This means higher order consumers will experience increased contamination from a chemical substance

    • Diagram of effect:

  • S: Analysis of data illustrating the causes and consequences of biomagnification

    • Dichloro Diphenyl Trichloroethane (DDT) is an example of a chemical substance which is biomagnified

      • DDT = a chemical pesticide that is sprayed on crops to eliminate mosquito larvae and washed into waterways at low concentrations

        • Taken up by algae and passed on to primary consumers

      • DDT is fat soluble and selectively retained within the tissues of an organism instead of being excreted

    • At each subsequent trophic level DDT is passed on through the algae, the concentration of DDT stored in the body increases

      • Increased trophic level = increased food uptake = increased DDT

      • Very high levels of DDT were discovered in birds that preyed on fish

    • Birds exposed to high levels of DDT through feeding on fish that fed on algae were found to produced thinner shells as a consequence

      • This decreased survival rates of fledglings

    • Diagrams we may encounter for such data analysis

  • A: Discussion of the trade-off between control of the malarial parasite and DDT pollution

    • DDT was widely employed as a chemical pesticide in the 1940s and 1950s to control insect-borne diseases like malaria

      • Agricultural insecticide

      • Led to complete eradication of malaria in many high socioeconomic world regions

      • Less effective in low socioeconomic tropical regions where eradication programs could not be sustained

    • Eradication programs were curtailed by the World Health Organization (WHO) in 1969

      • For safety and environmental concerns

      • DDT can bioaccumulate to toxic levels and poses a significant threat to high trophic levels due to biomagnification

      • Current interventions for malaria now focus on non-spraying strategies

        • E.g. the use of bednets soaked in insecticides

    • Malaria vs. DDT

      • Arguments for DDT spraying:

        • DDT spraying is an affordable and effective means of killing mosquitos that carry disease

          • E.g. malaria, dengue fever, etc.

        • Where the use of DDT has been discontinued, the incidence of malaria and associated deaths have increased

        • Health costs associated with the treatment of malaria are reduced when DDT spraying is implemented

        • Alternative strategies are not as cost-effective or successful

      • Arguments against DDT spraying

        • It is associated with adverse health effects in humans

          • E.g. cancer, birth defects, reduced fertility, etc.

        • Persists in the environment for long periods of time

          • More than 15 years

        • DDT is biomagnified in higher order consumers which has adverse consequences on ecosystems

• Plastic pollution

  • U: Macroplastic and microplastic debris has accumulated in marine environments

    • Plastic = a type of synthetic polymer

      • Found in certain types of clothes, bottles, bags, food wrappings, containers, etc.

      • Most plastics are not biodegradable → persist in the environment for many centuries

    • Macroplastic = large visible plastic debris

      • 1 mm

      • Macroplastic debris can be degraded and broken down into microplastic debris by UV radiation and the action of waves

    • Microplastic = smaller plastic debris

      • < 1 mm

    • Ocean currents will concentrate plastic debris in large oceanic convergence zones called gyres

    • Plastic debris in the ocean will leach chemical into the water + absorb toxic contaminants called persistent organic pollutants

      • Microplastics will absorb more persistent organic pollutants (POPs) due to their smaller size

        • More surface area available

    • Both macro- and microplastic debris is ingested by marine animals, which mistake the debris for food

      • This leads to the bioaccumulation and biomagnification of POPs within marine animals

      • It may also damage the stomach of animals or cause them to stop feeding

        • By taking up space in the digestive tract

    • Diagram:

  • A: Case study of the impact of plastic debris on Laysan albatrosses and one other named example

    • Case Study 1: Laysan Albatross

      • Nests on islands found in the North Pacific gyre where large amounts of plastic debris is found

      • Feeds by skimming the ocean surface with their beak → this causes them to ingest large quantities of plastic too

      • Adults can regurgitate (throw up) the plastic they have swallowed, but chicks are unable to

        • Instead, it fills up their stomachs

        • The mortality rate in albatross chicks is very high

          • Estimated 40% die before fledgling

    • Case Study 2: Sea turtles

      • Will commonly mistake plastic bags for jellyfish

        • Jellyfish = one of their primary food sources

      • Ingestion of the plastic can be fatal

        • It can become lodged in the esophagus and cause future feeding problems

      • Plastic debris can also become wrapped around the turtle → restricting movement and developmental growth

      • It is estimated plastic pollution harms ca. 100 000 sea turtles and other marine animals each year

• EC: Cholorfluorocarbons

  • Chlorofluorocarbons (CFCs) = chemicals widely used as refrigerants, propellants and solvents in the past

    • Contribute to ozone depletion in the upper atmosphere

      • Therefore their manufacture and use is being phased out

  • Ozone layer = stratospheric region composed of ozone (triatomic oxygen)

  • CFCs are broken down by UV radiation to release chloride ions that react with ozone

    • The ions breaks the ozone down into oxygen

    • One chloride ions can destroy 100 000 ozone molecules

    • Diagram of the process:

  • Ozone in the stratosphere absorbs UV radiation, however there is a limit to how much radiation ozone can absorb

    • Regions where the ozone layer is thinner will experience higher terrestrial UV levels

      • Thinning caused by for example CFCs

    • UV light penetrates tissues and damages DNA → this causes gene mutations and cancer

    • Can also damage the ability of plants to carry out photosynthesis + kill phytoplankton → this reduces productivity

• EC: Earth spheres

  • The Earth is made up of four distinct and connected spheres

    • Lithosphere, hydrosphere, atmosphere, biosphere

    • 

  • Lithosphere = all the rocks, minerals and molten magma found on or in the Earth

    • Also called geosphere

  • Hydrosphere = all the water on Earth

    • Liquid water such as oceans and rivers

    • Precipitation and vapor

  • Atmosphere = the layer of gasses surrounding the Earth

    • Divided into further sections

    • E.g. stratosphere

  • Biosphere = all the living organisms on the planet

    • Including plants, animals, bacteria, etc.

  • As the four spheres are interconnected, human impact on one sphere will potentially affect other spheres

    • Examples:

      • The release of plastic pollution into the hydrosphere (oceans) will impact the biosphere (marine life)

      • The production and release of CFCs into the atmosphere will impact how much UV radiation the biosphere is subjected to

C4 Conservation of biodiversity

• Indicator species

  • U: An indicator species is an organism used to assess a specific environmental condition

    • Indicator species are sensitive to specific environmental conditions → limited range of tolerance

      • Reduction or growth of their population therefore indicates changes in the environment

        • Useful means of monitoring change

    • Examples of indicator species and their environmental conditions

      • Lichen and mosses are susceptible to air-borne pollutants dissolved in water

        • E.g. sulfur dioxide

      • Tubifex worms are sensitive to concentrations of heavy metals

      • Mayfly larva and certain aquatic invertebrates are sensitive to dissolved oxygen levels in water

    • Diagram:

  • U: Relative numbers of an indicator species can be used to calculate the value of a biotic index

    • Biotic indices compare the relative frequency of indicator species

      • • Provide an overall assessment of environmental health

    • Calculating a biotic index involves multiplying the population size of each indicator species by its pollution tolerance rating

      • 

    • The following conclusions can be drawn from a biotic index:

      • A high biotic index = the presence of many pollution-sensitive organisms

        • Denotes an unpolluted environment

      • A low biotic index = the absence of pollution-sensitive organisms + abundance of pollution-tolerant organisms

        • Indicates a polluted environment

      • A change in the biotic index over time marks a change in the environmental conditions within a given ecosystem

    • Pollution tolerance rating

      • 

    • Environmental pollution levels

      • 

• Biodiversity

  • U: Richness and evenness are components of biodiversity

    • Biodiversity = the variety and variability of all living organisms within a given ecological area

      • Can be used to refer to the number of species, their genetic diversity or habitat variety

        • Habitat variety = ecological variations

    • 2 main components contribute to biodiversity

      • Species richness → the number of different species present in an area

        • More species = greater richness

      • Species evenness → the relative abundance of the different species in an area

        • Similar abundance = more evenness

      • Richness vs. evenness

  • S: Analysis of the biodiversity of two local communities using Simpson’s reciprocal index of diversity

    • Simpson’s reciprocal index can be used to measure the relative biodiversity of a given community

      • It takes into account both the number of species present (richness) and the number of individuals per species (evenness)

      • A higher index value is indicative of a greater degree of biodiversity within the community

    • 

    • Simpson’s reciprocal index can be used to compare communities to identify intrinsic values

      • Intrinsic value = something we value for itself, not its consequences

      • A high index value = a stable site with many different niches and low competition

        • High richness and evenness

      • A low index value = a site with few potential niches where only a few species dominate

        • Low richness and evenness

      • The index value may change in response to ecological disturbance

        • E.g. human intervention, natural disasters, etc.

• Biogeographic factors

  • U: Biogeographic factors affect species diversity

    • Biodiversity within a given ecosystem will be affected by a number of biogeographic factors

      • Larger habitats tend to promote biodiversity better than smaller ones

        • More available niches = less competition

      • Ecology at the edges of ecosystem is different from central areas

        • E.g. more sunlight, more wind, etc.

        • This is known as the edge effect, whereby species distribution is influenced by divergent environmental conditions

        • Edges tend to have greater biodiversity as different habitats with different abiotic factors exist in close physical proximity

        • However, edges tend to have more competition than central regions → may restrict survival prospects of certain species

      • Habitat corridors between parts of a fragmented habitat can connect disparate regions to improve genetic diversity

    • These principles of biogeographic factors are routinely applied when setting aside land as a nature reserve to improve the conservation of biodiversity

      • 

  • A: Analysis of the impact of biogeographic factors on diversity limited to island size and edge effect

    • Island size

      • The biodiversity of an island is typically proportionate to island size

        • Larger island = greater biodiversity

          • Larger islands support a greater range of habitats

            • Hence more available niches for species to occupy → more survival + diversity

          • Larger islands can sustain higher population numbers for each species

            • Increases species evenness

          • Larger islands have greater productivity at each trophic level

            • Leads to longer + more stable food chains

        • Smaller island = less biodiversity

        • Diagram depicting the relationship between island size and biodiversity

    • Edge effect

      • The diversity of species within a given environment changes with proximity to the ecosystem’s boundaries

      • Biodiversity may be greater at the border between two ecosystems as different abiotic factors favor certain species

      • However, certain species may not be able thrive under these conditions

        • Instead must occupy more central regions

      • The effect of edges on biodiversity will be greatly influenced by the particular conditions caused by the ecological disturbance

      • Diagram:

• Conservation

  • U: In situ conservation may require active management of nature reserves or national parks

    • Conservation = the careful preservation, protection and maintenance of natural resources

      • Such as trees, water, wildlife, etc.

      • Can be either in situ or ex situ

        • On site or off site

    • In situ conservation is the preservation of plant and animal species within their natural habitat

      • Typically involves the designation of protected areas of land as either nature reserves or national parks

    • These areas may require active management to ensure that an appropriate and sustainable ecological balance is maintained

      • Ecological monitoring of a species may be required to ensure viable population levels are maintained

      • Interventions may be required to prevent habitat degradation or competition from invasive species

      • Legislation may be necessary to ensure adequate funding for policing and education

    • In situ conservation offers several advantages when protecting endangered species from extinction

      • It allows species to live in the environment to which they are adapted

        • + to occupy their natural position in the food chain

      • It maintains the animal’s normal behavior

        • Offspring usually acquire skills from parents and peers around them

      • Retaining the natural habitat prevents its eventual loss + ensures it remains available for other endangered species

        • Such areas provide a place to return animals from breeding programs as they provide realistic conditions for reintegration

      • Reserves in different areas can share information and provide a place for scientific study and developing public awareness

  • U: Ex situ conservation is the preservation of species outside their natural habitats

    • Ex situ conservation involves the preservation of plant and animal species outside their natural habitats

      • May typically be required for critically endangered species when urgent intervention is necessary

    • There are several advantages associated with ex situ conservation

      • It allows for greater control of essential conditions

        • E.g. climate control, dietary intake, veterinary care, etc.

      • It can improve the chances of successful breeding by utilizing artificial methods

        • E.g. embryo transfer, IVF, etc.

    • Ex situ conservation is also associated with several disadvantages

      • They do not prevent the potential destruction of their natural habitats

      • Species raised in captivity are less likely to be successfully reintroduced into the wild

        • Loss of autonomous survival

      • Increases inbreeding by restricting the gene pool → restricts the evolution of the species

    • Some examples of ex situ conservation measures employed around the world:

      • Captive breeding → animals are raised and bred in containment to ensure survival prospects

        • E.g. zoos

      • Botanical gardens → areas devoted to the collection, cultivation and display of a wide variety of plant species

      • Seed banks → secure sites that store and catalog seeds in order to preserve plant genetic diversity

  • A: Case study of the captive breeding and reintroduction of an endangered animal species

    • Case Study 1: Indian rhinoceros

      • An endangered species with only ca. 3500 rhinoceros living in the wild

        • This number was as low as 2000 in the early 1990s → increased due to successful captive breeding programs

      • In addition to habitat loss, the Indian rhinoceros is threatened by poachers

        • Their horn is considered potent in some cultures

      • It is listed as vulnerable on the IUCN red list + the majority of the species is situated in Indian protected areas (reserves)

    • Case Study 2: Mountain Chicken Frog

      • A species of frog native to the Carribean islands of Dominica and Montserrat

      • The population of this frog has declined i81% in the last 10 years

        • Due to the fungal disease chytridiomycosis

        • Also threatened by human consumption → local delicacy said to taste like chicken

      • Considered critically endangered with fewer than 8000 individuals existing in the wild

      • The frog has been artificially bred in laboratories in England prior to being reintroduced into the wild

• EC: Endangered species

  • Endangered species = categorized by the International Union for Conservation of Nature (IUCN)  as likely to become extinct

    • Conservation status = likelihood of becoming extinct

  • Currently 3000 endangered species according to IUCN

  • Factors for determining a species’ conservation status

    • Rate of decline

    • Population size

    • Area of geographic distribution

    • Degree of population fragmentation

  • IUCN has a red list which classifies species into nine groups

    • Extinct (EX)

      • No surviving individuals

      • E.g. tasmanian tiger

    • Extinct in Wild (EW)

      • Captive individuals survive, but there is no wild population

      • E.g. barbary lion

    • Critically endangered (CR)

      • Faces an extremely high risk of extinction in the near future

      • E.g. red wolf

    • Endangered (EN)

      • Faces a high risk of extinction in the near future

      • E.g. snow leopard

    • Vulnerable (VU)

      • Faces a high risk of endangerment in the medium term

      • E.g. Indian rhinoceros

    • Near Threatened (NT)

      • May be considered threatened in the near future

      • E.g. tiger shark

    • Least Concern (LC)

      • No immediate threat to species survival

      • E.g. giraffe

    • All other organisms may be listed as Data Deficient (DD) or Not Evaluated (NE)

• EC: Extinction

  • Extinction = the complete cessation of a species or higher taxon level, reducing biodiversity

  • Can occur gradually as one population of organisms evolves into something else

    • Phyletic extinction

  • Can be sudden without any identifiable descendents → cease to exits

    • Abrupt extinction

  • Can be very difficult to determine the moment of extinction → most categorizations are usually done retrospectively

    • Occasionally species thought to be extinct can be rediscovered after a period of time

      • E.g. lazarus taxa

  • 99% of all species that ever lived on Earth are considered to be extinct

    • Estimated to amount over 5 billion species

    • Natural catastrophes may cause mass extinction events

      • Large scale loss of species in relatively short period

  • Case Study: Tasmanian Tiger

    • Thylacinus cynocephalus

    • Became extinct after the arrival of European settlers to Australia

    • Tasmanian tigers would feed on introduced sheep → therefore hunted and poached

    • The loss of habitat due to human development + lack of successful breeding programs = population numbers dwindling

      • Aboriginal rock paintings suggest the Tasmanian tiger once lived on the mainland, but died out from predation and/or competition

    • Last Tasmanian tiger died in captivity in 1936

      • Declared extinct by international standards in 1986