IB BIO HL UNIT 6 --- Ecology

Ecology Definition

The scientific study of interactions among organisms and between organisms and their environment (organisms are interdependent with each other and with environment

Ecological Classification - Individual

The singular organism

Ecological Classification - Population

Group of organisms of the same species living in the same area at the same time that can typically interbreed (common gene pool)

Populations are reproductively isolated from other populations

Ecological Classification - Community

All populations living together within a defined area — all the biotic factors

Involves interspecific and intraspecific interactions, forming complex ecological relationships = improved function

Ecological Classification - Ecosystem

All biotic and abiotic factors

Ecological Classification - Biome

A group of ecosystems sharing similar climates and typical organisms (same abiotic and biotic factors)

Ecological Classification - Biosphere

Our entire planet, including all organisms and physical environments

Biotic Factors

Living/biological influences on an organism

ex. predator, prey, food availability

Abiotic Factors

Non-living influences on an organism

ex. soil, water

Most general → Most specific levels of ecological classification

Biosphere, Biome, Ecosystem, Community, Population, Individual

Open Ecosystem

Energy and Matter can leave the ecosystem naturally or with human involvement

Examples of natural movement in/out of ecosystem

Migration + Gene Flow

Examples of human-caused movement in/out of ecosystem

Housing Developments + Deforestation

Closed Ecosystem

Only energy can enter/exit ecosystem

Mesocosm

Example of a closed ecosystem — only energy can enter/exit; an outdoor experimental system created by humans to examine natural environments under controlled conditions

Photosynthesis

Allows organisms to harness the energy in sunlight (unit 5)

6CO2 + 6H2O → C6H12O6 + 6O2

Autotrophs (AKA producers)

Organisms that can produce their own organic molecules to be broken down into ATP energy — also called Producers

Photoautotrophs

Type of autotroph that uses light energy to produce organic molecules → ATP

ex. plants, cyanobacteria, algae

Chemoautotrophs

Type of autotroph that obtains energy through the oxidation of inorganic compounds like Iron, Sulfur, + Magnesium

ex. extremophiles — live near hydrothermal vents

Heterotrophs

Organisms that cannot produce their own organic molecules, which must be obtained from other organisms

Holozoic Nutrition

Organisms that take in solid/liquid food internally

Consumers

Heterotrophs that eat other organisms for energy

Herbivore

A consumer that eats producers (plants)

ex. Cows, Deer, Goats, Caterpillars

Carnivore

A consumer that kills and eats other consumers

ex. Lions, Snakes, Cats

Omnivore

A consumer that is both carnivorous and herbivorous — eats both plants and other animals

ex. Humans, Bears, Pigs

Scavenger

A consumer that eats the carcasses of other animals

ex. Vultures, Hyenas, Condors

Decomposers

Break down dead organisms + organic matter — extracts nutrients from decaying matter (ex. feces, leaf litter) and returns it to soil, making it available for reuse

ex. Bacteria, Fungi, Invertebrates

Saprotrophs

Decomposers that obtain organic nutrients from dead organisms with external digestion

ex. Fungi + Bacteria

Detritivores

Decomposers that obtain organic nutrients from detritus (organic matter created during decomposition of dead organisms) with internal digestion

ex. Earthworms, millipedes, snails

External digestion

Used by saprotrophs — the process of secreting hydrolytic enzymes to breakdown molecules in order to absorb nutrients

Internal Digestion

Used by detritivores — nutrients are consumed and broken down internally with enzymes (**part of Holozoic nutrition)

Arrows in a food chain/web

Show the direction of transfer of energy and biomass

Biomass (how is it related to energy?)

Biomass = the total dry mass of a group of organisms in a specific area or volume

Biomass contains energy

How does energy loss limit the food chain?

Only 4-5 trophic levels are possible:

energy loss limits energy stored as biomass at each level, making the amount of energy available at higher levels inefficient to sustain another one.

Five Trophic Levels

First → Producer

Second → Primary Consumer

Third → Secondary Consumer

Fourth → Tertiary Consumer

Fifth → Quaternary Consumer

How can an organism act as 2 different trophic levels in a food web?

An organism can obtain energy from one organism and produce energy for another

Why aren’t decomposers typically included in a food chain/web?

Decomposers don’t typically interact with other organisms while helping with the recycling of nutrients in ecosystems

What is the use of energy once organic molecules are made (for both autotrophs and heterotrophs)?

Some is stored, but most is used for cellular respiration

10% rule

On average, only 10% of energy is available @ lower trophic levels to be transferred to the higher trophic levels

5 sources of energy loss in an ecosystem

1. Heat Dissapation as a byproduct of metabolic reactions

2. Incomplete Consumption - all of the biomass in food isn’t fully consumed (ex. bones)

3. Inefficient Digestion - 100% of energy from food cannot be absorbed

4. Metabolic Processes - extracted energy used to perform certain functions, making that energy unavailable for consumption

5. Inefficient Conversion/Storage - not 100% of energy can be stored in an organism

Energy Pyramid

A diagram to represent the amount of available energy for each trophic level

Units = energy/area/time (ex. kJm^-2year^-1)

Primary Productivity

Rate at which producers accumulate carbon compounds in their biomass (aka rate of photosynthesis and storage of organic molecules)

Impacted by:

• temperature

• precipitation

• nutrient availability in soil

(more sun, water, and nutrients = more primary productivity)

Primary Productivity & Ecosystem diversity

Greater producer biomass can support a greater number and diversity of consumers in an ecosystem

GPP - Gross Primary Productivity

Total amount of energy captured as biomass by primary producers in an ecosystem

NPP - Net Primary Productivity

Energy available to consumers at higher trophic levels

Relationship between GPP and NPP

NPP = GPP - R

^ Net primary productivity = Gross Primary Productivity - Energy Loss due to respiration

Secondary Productivity

Rate at which consumers accumulate carbon compounds as a part of their biomass

GSP - Gross Secondary Productivity

Total biomass assimilated by heterotrophs in an ecosystem

NSP - Net Secondary Productivity

Remaining biomass after accounting for respiratory losses

Relationship between GSP and NSP

NSP = GSP - R

^ Net Secondary Productivity = Gross Secondary Productivity - Energy Loss due to respiration

Carrying Capacity

The maximum population size of a species that can be sustained long term by a given environment

influenced by available resources, making it dynamic

Limiting Factor

Environmental factors that restrict the growth, distribution, or abundance of a population or organism within an ecosystem

Density-Dependent Limiting Factor

Have a greater impact on population size as the population density increases

Due to interspecific and intraspecific competition

Example of Density-Dependent Limiting Factors

• Competition for Resources - bigger population = more competition for resources

• Predation - the more prey available, the more predators will kill

• Disease/Parasites - bigger population = disease will spread more

What do density-dependent limiting factors maintain?

The carrying capacity

Interspecific competition

Competition between organisms of different species

Intraspecific competition

Competition between organisms of the same species

Density-Independent limiting factors

Has an impact on population size regardless of population density.

External factors that cause drastic changes - typically abiotic

Example of Density-Independent Limiting Factors

Natural Disturbances: Floods, Droughts, Hurricanes, Earthquakes, Eruptions, etc.

Anthropogenic Events: Habitat Destruction, Pollution, Climate change

Shape of the Exponential Growth Curve

J-Shaped curve

Conditions for exponential growth

Ideal conditions:

• Unlimited resources

• biotic and abiotic factors are favorable

• well below carrying capacity

ex. Bacterial Growth in a lab

How does exponential growth relate to carrying capacity?

Exponential growth only occurs when population density is well below the carrying capacity (room for growth)

Shape of the Sigmoid growth curve

S-shaped curve

Conditions for sigmoid growth

Environments with limited resources (more typical than exponential growth)

3 Phases in a sigmoid growth curve

1. Exponential growth phase — when population is well below the carrying capacity

2. Transitional phase — environmental resistance becomes a factor; as population grows, density-dependent factors increase = growth slows

3. Plateau phase — population reaches equilibrium around the carrying capacity where the birth rate = the death rate

4 Factors that impact population growth

• Natality (N) = Birth Rate

• Immigration (I) = Individuals entering population

• Mortality (M) = Death Rate

• Immigration (E) = Individuals leaving population

Population Growth Formula

(N+I)-(M+E)

What Growth Phase is when N+I significantly greater than M+E?

Exponential growth phase (population is growing rapidly)

What Growth Phase is when N+I slightly greater than M+E?

Transitional growth phase (population is growing slowly)

What Growth Phase is when N+I equal to than M+E?

Plateau phase (0 population growth)

Intraspecific interactions

Interactions between organisms of the same species, including competition and cooperation

these interactions drive population dynamics and resource use

Intraspecific competition

Organisms of the same species compete for the same limiting resources (food, shelter, mates)

Can lead to adaptation of individuals to different niches, displacement, or regulation of population size

DENSITY DEPENDENT

Intraspecific cooperation

Organisms of the same species collaborate to increase their chances of survival and reproduction

• defense against predators

• shared parenting

Interspecific interactions

Interactions between organisms of different species within an ecosystem

Interspecific interactions - Herbivory

Feeding Relationship: herbivore eats plant material as primary source of nutrients — ex. Panda, Parrot fish

Herbivores have adapted specialized traits to effectively extract nutrients from plants — ex. Incisors, molars, teeth growth

Interspecific interactions - Predation

Feeding Relationship: predator captures and consumes its prey — Grizzly Bears, Wolves

***Plays a key role in shaping behavior, population size, and reproductive success as a density dependent limiting factor

Cycle of predator-prey relationships

Cyclical pattern of population increases + decreases

Prey # increases = Predator # increases = Prey # reduces = Predator # reduces = Prey # increases (cycle)

A “lag time” is seen in graphs due to this cycle

Interspecific Competition

Competition between different species for the same limited resources — ex. Eastern grey squirrel and American red squirrel compete for food

Impacts species distribution, abundance, and evolution of traits related to resource aquisition

How can you test for interspecific competition?

By removing one species from the ecosystem — if the second species is more successful, this suggests interspecific competition

Symbiotic Interactions

2 organisms living and interacting closely with each other where at least one organism benefits

Parasitism

One organism (the parasite) is helped and the other organism (the host) is harmed: +/- — ex. Tapeworms

**evolved to minimize damage to keep host alive longer**

Pathogenicity

Similar to parasitism except the pathogen immediately harms the host, disturbing its typically functions and spreading more rapidly:

One organism (the pathogen: a virus, bacterium, or fungus) is helped and the other organism (the host) is harmed: +/-

ex. Protist

Commensalism

One organism is helped an the other is neither helped nor harmed: +/0

ex. Orchids growing on branches of trees

Mutualism

Both organisms are helped by the relationship: +/+

ex. Root Nodules in Legumes

Mutualism example — Root nodules in Legumes

• Root Nodules contain nitrogen fixing bacteria that provides legumes with usuable nitrogen

• Legumes provide bacteria with carbohydrates and other organic molecules

Mutualism example — Mycorrhizae in Orchids

• Fungi forms Mycorrhizae to increase the surface area for nutrient absorption in soil

• Orchids provide fungi with organic compounds

Mutualism example — Zooxanthellae in Hard Corals

• Zooxanthellae (unicellular photosynthetic algae) within corals provide organic molecules and pigmentation to prevent UV exposure

• Hard corals provide zooxanthellae with shelter and easy access to sunlight

Endemic Species

Species native to the location

Introduced/Alien Species

Species that are non-native and introduced by humans

ex. Kudzu in Georgia, Lionfish in carribean

What causes an introduced species to become invasive?

When it causes harm to the ecosystem by outcompeting endemic species:

• rapidly increase in #

• more efficient in resource use

• no natural predators present

alien species are detrimental to the biodiversity of an ecosystem

Process of Kudzu becoming invasive in Georgia

1. Native to Japan and China

2. Introduced in the U.S. to prevent soil erosion

3. Grew 1ft/day

4. Outcompeted native species by shading plants

5. resulted in loss of biodiversity

Top-Down control

Prescence and activites of organisms in the higher trophic levels regulates the abundance/behavior of lower trophic levels — PREDATION

Grey Wolves as example of Top-Down control

Reintroduction of Grey wolves into yellowstone impacted many lower trophic levels in the ecosystem, imrpoving the stability of the ecosystem (trophic cascade + keystone species)

Bottom-Up control

Availability of organisms at lower trophic levels influences the abundance/distribution of organisms at higher trophic levels

ex. Nutrient Availability in Soil determines growth of plants which determines herbivore # = determines predator # (trophic cascade)

Trophic Cascade

disruptions in lower/higher trophic levels of the food chain has indirect implications along all other levels

Allelopathy

Organisms release biochemical compounds into the environment = infuences the growth, survival, or reproduction of other organisms in the area

ex. toxic chemicals from tree roots injures/kills nearby sensitive trees

Antibiotic secretion

Some microorganisms (fungi + bacteria) can secrete antibiotics to hinder the growth of bacteria

ex. Penecillium mold naturally produces antibiotic penecillin, Streptomyces bacteria can synthesize antibiotics like streptomycin

3 R’s of population sampling

Random, Repetitive, Representative

Critical to give an accurate representation of the population as a whole (minimized bias)

Quadrat Sampling

Used for sessile (non-moving) organisms;

1. A quadrat is placed randomly in a section of habitat

2. the # of organisms of interest within the quadrant is recorded

3. mean # of organisms in each quadrant calculated

4. total population size estimated based on area of quadrant vs. total area

Define Quadrat

A square frame of known area used for sampling in ecological studies