HL Biology Unit 4 Ecology

Species

Organisms that can potentially interbreed to produce fertile offspring (mules are HYBRIDS, but they don’t have fertile offspring)

Reproductive Isolation

Members of a species may be isolated in different populations or by location or behavior → eventually they may not be able to reproduce with other members anymore → new species (speciation)

Autotrophic Species

Generates organic nutrition from inorganic substances

Heterotrophic Species

Feeds on other organisms for nutrition

Mixotrophic

Uses more than one method for organic nutrition (ex. Euglena algae are both hetero and autotrophic)

Photoautotrophs

Generate organic nutrition by harvesting light energy

Chemoautotrophs

Generate organic nutrition through oxidation of inorganic compounds

Detritivores

Ingest detritus by internal digestion

Saprotroph

Decompose detritus by external digestion (ex. mycelium hyphae release digestive enzymes onto a material to break it down before absorbing it)

Population

Members of the same species in an area at a given time

Community

All populations living and interacting with each other in an area

Ecosystems

Organisms in interaction with their environment, both biotic and abiotic factors

Quadrat Sampling

-used for sessile organisms that don’t move around much

-uses a large grid, smaller areas within the grid are chosen randomly and their averages are used to estimate pop. size

Sampling Error

The difference between the estimated population size and the true size of the population

“Capture-mark-release-recapture” Sampling and its assumptions

-used for motile organisms that move around environment

-measured using the Lincoln Index

Assumptions

1. The population is a closed system

2. The time between samples is very small

3. The marked organisms mix freely and completely within the population

Lincoln Index

pop. size estimate = M(N/R)

M = # of individuals marked initially

N = total # of individuals recaptured

R = # of marked individuals recaptured

Limiting Factors

Anything that constrains a population’s size and slows/stops it from growing

Carrying Capacity

The number of individuals that an ecosystem can sustainably support

Negative Feedback

A change in conditions that causes a reaction in the opposite direction (if something increases, negative feedback decreases it to maintain status, or vice versa)

Density Dependent Factors

Reduce pop. size when an area’s too densely populated (ex. Prey and Predator control e/o pop., or pathogens)

Density Independent Factors

Impacts a population regardless of its density (ex. natural disasters)

Interspecific Competition

Competition between DIFFERENT species

Intraspecific Competition

Competition WITHIN a species, where better adapted organisms survive and reproduce, leading to evolutionary diversity

Phases of an idealized Sigmoid Population Growth Graph

Exponential Curve: Stage of exponential growth where there are few factors to affect pop. size

Transitional Phase: As pop. grows, density dependent factors provide negative feedback

Plateau Phase: Population reaches carrying capacity

Can be modeled by duckweed and yeast growth

Ecological Niche

An organism’s role within an ecosystem that includes the spatial habitat and its interactions with other species

Competitive Exclusion Principle

States that two species cannot survive indefinitely in the same ecological niche (besides scenarios like cohabitation, but that leads to competition)

6 types of interspecific relationships

Herbivory, Predation, Mutualism, Parasitism, Interspecific Competition, Pathogenicity

Herbivory interspecific interactions

Where primary consumers ingest producers

Predatory interspecific interactions/Predation

Where consumers feed on another consumer

Mutualism

Where two (often distantly related to avoid competition) species benefit from their relationship

ex. Root nodules in Fabacea, Mycorrhizae in Orchidaceae, Zooxanthellae in coral polyps

Explain the mutualistic relationship between Rhizobia and Fabacea

Rhizobia infect Fabacea and form root nodules and convert atmospheric N to a usable form for the plants while they receive organic nutrition from the plant roots

Explain the mutualistic relationship between Zooxanthellae and Coral

Coral polyps produce CO2 as waste, and the zooxanthellae need CO2 for food. The coral provides the zooxanthellae with shelter and CO2 for food, so the zooxanthellae gets rid of waste for the coral

Explain the mutualistic relationship between Mycorrhizae and Orchidaceae

Orchids rely on the mycorrhizae in early life to get all its food from external digestion while the fungi receives food through the orchid’s carbohydrates → they both get food off each other

Parasitism

When one organism feeds off another (usually) without killing it

Pathogenicity

Pathogens are an example of interspecific relationships because they often have specific host organisms

Zoonotic Infection

When a pathogen evolves so that it can spread to different species (ex. bird flu)

Invasive Species

Species that outcompete or have negative impacts on endemic species

-If humans introduce them to a new area, they experience fewer limiting factors and experience rapid population growth

(ex. Red Lionfish)

Field Manipulation Studies

Studies that can be used ot measure the effects of potential invasive species, where one species is removed from the experimental area to see its effects

Allelopathy

The chemical inhibition of one plant by another due to the release of substances acting as germination/growth inhibitors into the environment

(ex. antibiotics produced naturally by fungi to control microbial populations, specifically penicillin making penicillin)

Null Hypothesis (about population distribution)

States that there is no significant difference between the distribution of two species (random distribution)

Alternative Hypothesis (about population distribution)

States that there is a significant difference between the distribution of species (species are therefore associated)

Using the Chi-Square test to measure the distribution between species

1. Make a table measuring the frequency that of each species: species 1 only, species 2 only, both, none

2. Create a contingency table using those values to find the total of when each species is present

3. Create an expected frequency table using the expected frequency formula

4. Create the final chi-squared table using the chi-squared formula

5. Find degrees of freedom to determine if chi-square value is significant

Expected Frequency Formula

from contingency table:

(Row total x Column Total)/ Grand Total

Chi-squared formula

For two species, the sum of (o-e)²/e of the 4 different X² values

Degrees of Freedom Formula

(m-1)(n-1)

m = # of rows

n = # of columns

Bioaccumulation

The absorption of toxins into an organisms body tissue over time

Biomagnification

When toxins are not excreted in orgasnisms and therefore become more concentrated in tissues of higher trophic levels as feeding occurs

(ex. DDT pesticides in aquatic animals/plants → raptors → weak egg shells, or macro/microplastics)

Rewilding

The restoration of natural processes in ecosystems by positive interventions (ex. the forests of Hinewai Reserve have now mostly recovered)

Cyclical Oscillators of Predator Prey Relationships as Density-Dependent Population Control

more prey → more food for preds → more pred pop → more predation → less prey pop → less pred food → less pred pop → less predation → more prey pop…. repeats

Where are cyclical oscillations usually observed?

Habitats where the weather conditions vary from year to year: when beneficial weather occurs one year, the cycle starts from increased producers/prey

Direct interactions between trophic levels

When sequential trophic levels interact with each other, ex. herbivores eating producers

Indirect interactions between trophic levels

When a trophic level has an indirect effect on a non-sequential trophic level, ex. predators decrease herbivore pop, therefore increasing producer pop

Top-Down Population Control

Population control that occurs from changes in a higher trophic level that affects a lower trophic level ex. more preds = less prey

Bottom-Up Population Control

Population control that occurs from changes in a lower trophic level that affects a higher trophic level ex. less water nutrients = less producer pop

Primary Production

The amount of solar energy converted to chemical energy, carried out by producers and measured as the amount of carbon compounds in the biomass produced by autotrophs (usually gm-²yr^-1)

Net Primary Productivity equation

Net Primary Productivity = Gross Primary Productivity - Respiration

List of biomes from most to least amount of primary productivity

Tropical rain forest, temperate deciduous forest, savanna, taiga, cultivated land, temperate grassland, tundra

Algal beds, coral reeves, estuaries, open ocean

How/where does chemical energy flow after it is created during primary production?

It flows through the food chain and is lost between trophic levels bc the 2nd law of thermodynamics states that energy transformations are inefficient (10% rule)

How is energy lost between trophic levels?

1. Cellular respiration: food → ATP → lost as body heat

2. Food not being completely absorbed → chemical energy lost as waste

Secondary Production

The amount of carbon compounds in biomass formed by heterotrophs (gm-²yr^-1), ends up lower than primary production bc heterotrophs usually have increased metabolism and respiration

What happens after secondary production?

Nutrients are recycled

How is carbon cycled?

1. Oceans store dissolved CO2

2. Aquatic producers use CO2

3. Decomposers cycle nutrients ex. filter feeders like mussels

Carbon Flux

The movement of carbon

Carbon source

Sources of carbon that increase carbon flux (ex. respiration)

Carbon sink

Things that store carbon (ex. ocean, atmosphere)

What are the largest natural carbon sinks?

Atmosphere, Ocean, Fossil Fuels

What are abiotic requirements for ecosystem stability?

1. A steady supply of energy

2. Nutrient cycling without leakage from the ecosystem

3. Climate variation that is within tolerance

What are biotic requirements for ecosystem stability?

1. Biodiversity (many species)

2. Genetic diversity (within species)

Tipping Point

A threshold past which it is difficult/impossible for an ecosystem to recover, caused by things like deforestation

Describe the effects of deforestation

Positive Feedback Loop: tree removal → decreased rainfall → more drought/wildfire → less trees

Percent Change Formula

(Final-Initial)/Initial x 100 = %

Keystone Species

Species that have a disproportionate effect on the structure and sustainability of a community. The removal of these species affects several parts of the food web (ex. sea urchins controlling kelp forests)

Environmental Gradient

Things like altitude, latitude, soil horizons, tidal level, distance from water - all determined by distance usually

Transect Lines

Lines used to measure abundance and distribution along an environmental gradient, usually displayed on kite diagrams

Succession

The replacement of one community by another in an area over time due to changes in biotic/abiotic variables, a temporal phenomenon

Zonation

The gradual change in the composition of species/communities across a landscape based on environmental gradients, a spatial phenomenon

Primary Succession

Forms on newly formed substratum where there was not previously soil or communities

-new substratum formed by volcanos and glacial moraines

Pioneer Community

The first organisms to colonize new substratum, which then die and decompose to change the ecosystem to be more fertile for the next seral community

Secondary Succession

Succession occurring on bare soil where there were pre-existing communities

-bare soil could be caused by rewilding or forest fires

Factors that change during succession

1. Increased species diversity

2. More complex energy flow → more diversity → more complex food webs

3. Increased decomposition → increased soil depth

4. Increased nutrient cycling

5. Productivity….

How does productivity change during succession?

NPP initially high because all organisms are simple autotrophs, but later decreases as more heterotrophs are introduced and increase respiration

Ecological Disturbance

A short-term event that causes ecosystem changes that can be abiotic (flood, fires), biotic (new species, disease) or anthropogenic

What does an ecosystem’s ability to tolerate disturbances depend on?

The ecosystem’s diversity and resilience