CC

Option C: Ecology and Conservation

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:

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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