AP Bio Unit 8: Ecology

Ecology

The study of interactions between living and nonliving factors in the environment.

Biosphere

All the organisms and environments of the planet.

Ecosystem

Community plus its abiotic environment. Determined by abiotic factors, biotic factors, and factors intrinsic to organisms (adaptations).

Community

Interacting populations of different species in a particular area.

Population

Individuals of the same species that live, interact, and interbreed in a particular area at the same time.

Levels of Ecological Organization

Biosphere, [Biome], Ecosystem, Community, Population, & Organism

Biomes

Groups of ecosystems that have the same climate and dominant communities. Climate is the dominant factor that determines these.

Biogeography

The study of the geographic distribution of living things and the abiotic factors that affect their distribution.

Abiotic Facotrs

Nonliving things

Biotic Factors

Living things

Biogeochemical Cycles

Pathways that move elements between abiotic and biotic reservoirs and the processes that cycle matter between reservoirs. These pathways are interdependent.

Nutrient Cycling (Biogeochemical Cycles)

Nutrients move between living things and the atmosphere.

Water Cycle (Biogeochemical Cycles)

Abiotic reservoir - surface and atmospheric water

Enter food chain - precipitation and plant uptake

Recycle - transpiration

Return to abiotic - evaporation and runoff

Human impact - pollution; deforestation causes a reduction in transpiration 

Key processes - evaporation, condensation, precipitation, and transpiration (water leaving plant stomata

Carbon Cycle (Biogeochemical Cycles)

Abiotic reservoir - CO₂ in atmosphere

Enter food chain - photosynthesis = carbon fixation into carbohydrates in Calvin cycle

Return to abiotic - respiration and combustion

Human impact - burning of fossil fuels releases more CO₂ into the atmosphere; deforestation reduces # of plants performing photosynthesis

Key processes - photosynthesis, cellular respiration, decomposition, and combustion.

Nitrogen Cycle

Abiotic reservoir - N in atmosphere

Enter food chain - nitrogen fixation by bacteria (nitrogen gases are “fixed’ into ammonia, making it ionized and available to be turned into an organic compound)

Recycle - decomposition and nitrifying bacteria

Return to abiotic - denitrifying bacteria

Human impact -  runoff from fertilizer adds nitrogen to bodies of water → eutrophication; insecticides & herbicides can kill bacteria in soil

Ammonification

When plants or animals die (or leave behind waste), decomposers break down the remains and convert the organic nitrogen back into ammonia (NH₃), returning it to the soil.

Nitrification

Specific soil bacteria take that ammonia and turn it into nitrites (NO₂^-) and then into nitrates (NO₃^-). Nitrates are the form of nitrogen that plants find easiest to absorb during assimilation.

Denitrification

To complete the cycle, denitrifying bacteria in the soil take nitrates and convert them back into nitrogen gas (N₂), which is released back into the atmosphere.

Phosphorus Cycle

Abiotic reservoir - rocks, minerals, and soil

Enter food chain - erosion releases soluble phosphate (PO4 3-) that is taken up by plants & incorporated into biological molecules (DNA, RNA, ATP)

Recycle - decomposing bacteria and fungi

Return to abiotic - loss to ocean sediment

Human impact - runoff from fertilizer adds phosphorous to bodies of water → eutrophication

Eutrophication

A body of water becomes overly enriched with minerals and nutrients (N & P), leading to excessive growth of algae and depletion of dissolved oxygen.

5-Step Chain Reaction of Eutrophication

1. Nutrient Runoff

2. Algal Bloom

3. Light Blockage

4. Decomposition & Oxygen Depletion

5. Hypoxia & Die-off

Autotrophs

Producers, Captures “free energy” from physical or chemical sources (uses photosynthesis and chemosynthesis)

Chemosynthesis

Uses small inorganic molecules, can occur in anaerobic environments

Heterotrophs

Consumers, Captures energy by consuming organic matter produced by other organisms

Food Chain

Shows the feeding relationship between organisms

Trophic Level

A level in a food chain

Energy Pyramid

Represents the amount of energy at each trophic level in a food chain

10% Rule

Around 10% of an organism’s energy is passed to the next trophic level; the rest is lost to the environment as heat

Net Primary Productivity (NPP)

The measure of how much “new” energy or biomass is actually available to the consumers in an ecosystem.

Calculation: NPP = GPP - RL

Gross Primary Productivity (GPP)

The total energy captured by producers (via photosynthesis or chemosynthesis) per unit area/time.

NPP = GPP - RL

Respiration Loss (RL)

The energy producers use for their own metabolic needs (cellular respiration).

NPP = GPP - RL

Food Web

Shows interconnected food chains in an ecosystem

Endotherms

Generate heat to maintain their body temperature (food required)

Ectotherms

Do not regulate their own body temperature and only eat for energy needs. They may regulate their temperature behaviorally.

Metabolic Rate & Body Mass Relationship

Generally, the smaller the organism, the higher the metabolic rate.

Reproductive Strategies & Energy Availability

Organisms must balance energy cost of reproduction with the need to survive in their environment

→ Asexual Reproduction: low energy cost, high quantity of offspring, zero genetic diversity

→ SexualReproduction: high energy cost, lower quantity of offspring, high genetic diversity

Biodiversity

The variety of life in the world or in a particular habitat or ecosystem. Greater biodiversity means greater stability for an ecosystem (more resources, more food, etc)

Community Structure

Described in terms of species composition and species diversity. These measurements can change over time.

Species Composition

Specific types and relative proportions of species present in a community

Species Diversity

Both the number of species (species richness) and how equally represented each species is in a given area (species evenness)

Species Richness

The number of species

Species Eveness

How equally represented each species is in a given area

Simpson’s Diversity Index

A way to quantify biodiversity based on the number of species and the population size of each species (0 = no diversity (all the same), 1 = maximum diversity)

Keystone Species

Exerts important regulating effect on other species in community by increasing diversity in the habitat (ex: beavers build dams that transform streams into ponds).

Trophic Cascades

Ecological responses based on the addition or removal of top predators that results in dramatic changes in ecosystem structure and nutrient cycling.

Habitat

Where an organism lives

Niche

An organism’s ecological role in its environment

Symbiosis

Interaction between two organisms living in close association (can be positive, negative, or neutral for each of the organisms).

Mutualism

Both organisms benefit from the interaction.

Commensalism

One organisms benefits and the other is unaffected.

Parasitism

Parasite lives on or within the host causing it harm and benefiting from the host’s resources.

Amensalism

One organism harms another without any benefit to itself.

Competition

When two organisms attempt to occupy the same niche in the same habitat. One species will outcompete the other or they will divide the habitat (niche partitioning)

Resource Partitioning

Reduces competition through microhabitats. This occurs through adaptations, like different feeding times or using different parts of a habitat, allowing various species to coexist.

Coevolution

When two or more species reciprocally affect each other’s evolution (ex: parasite-host, flower-pollinator, predator-prey relationships)

Camouflage

To evade/hide from predators (cryptic coloration)

Defenses

Can be mechanical (ex: spines), or chemical (ex: odors)

Aposematic Coloration

Warning coloration; warns predators that they are undesirable to eat

Demography

The study of factors that affect the growth and decline of populations

Sex Ratio

A factor affecting population growth rate, asks how many males vs. females?

Generation Time

A factor affecting population growth rate, asks at what age do females reproduce?

Age Structure

A factor affecting population growth rate, asks how many females are at their reproductive age?

Survivorship Curve

A graphic way to represent population changes in a cohort still alive at each age

Birth-Death Model

N_t+1 = N^_t + B - D

BIDE Model

N_t+1 = N^_t + B + I - D - E

Limiting Factors: Density Dependent

Factor’s intensity changes based on how crowded the population is (ex: competition, predators, parasites, pathogens; typically biotic factors)

Limiting Factors: Density Independent

Factor affects the population regardless of its size (ex: sunlight, temperature, rainfall, etc; typically abiotic factors)

Carrying Capacity (K)

The maximum population size that environment (in an given area) can support without habitat degradation (affected by density-dependent and density-independent factors)

Exponential Growth Model

Occurs when resources are unlimited and limiting factors are absent

Logistic Growth Model

This incorporates density-dependent factors by accounting for carrying capacity

R Selected Reproductive Strategy

Early reproduction, many offspring, little parental care, type III survivorship curve

K Selected Reproductive Strategy

Late reproduction, few offspring, invests a lot in raising offspring, type I survivorship curve

Ecological Disturbances

Events that cause significant changes in an ecosystem, impacting both living organisms and the environment. They are often necessary for community development and survival because they release nutrients, increase biodiversity, increase habitats, and rejuvenate communities.

Invasive Species

Species that are transplanted from a different location and outcompete native species due to a lack of predators and reduce biodiversity

Ecological Succession

A series of progressive changes in the composition of an ecological community over time that often occurs after a disturbance

Pioneer Species

The first to grow or grow back after the disturbance that begins without soil (ex: bacteria, lichens, moss)

Climax Community

Stable community representing the final stage of succession

Secondary Succession

Existing community is cleared, but base soil is still intact (soil contains seeds and spores). Pioneer species of grasses and flowers.

Ecosystem Services

The direct and contributions of ecosystems to human well-being and quality of life.

HIPPCO (Human Impacts on Biodiversity)

Habitat Fragmentation/Loss, Invasive Species, Population Growth, Pollution (Pollutants), Climate Change, Over Exploitation

Adaptation

Genetic variation that is favored by selection that manifests as a trait that provides an advantage; can be structural, physiological, or behavioral

Heterozygote Advantage

Occurs when individuals with the heterozygous genotype (Aa) have greater fitness than both homozygous dominant (AA) and homozygous recessive (aa) individuals. When natural selection maintains both alleles in the population (balancing selection) rather than eliminating the "harmful" recessive one.

Behavioral Adaptions

A specific action or set of actions that an organism engages in to survive and reproduce in its environment. Natural selection favors innate and learned behaviors that increase an individual’s fitness and reproductive success.

Behavior

A response to internal changes (hormones, hunger, etc.) and external cues (temperature, light, etc.) in the environment

Innate Behavior

Inherited (instict), automatic, and consistent behavior (ex: migration patterns in birds)

Learned Behavior

Changes with experience and environment; the ability to learn is inherited but the behavior develops during an animal’s lifetime (ex: primates learning to use tools)

Tropism

A plant’s physiological response to environmental stimuli (phototropism, photoperiodism, gravitropism/geotropism, hydrotropism) and is controlled by a hormone called auxin.

Positive = towards stimulus, negative = away from stimulus

Phototropism

Growth in response to light

Photoperiodism

Blooming in response to light

Gravitropism/Getropism

Growth in response to gravity

Hydrotropism

Growth in response to water

Cooperative Behavior

Increases the fitness of the individual and the survival of the entire population (ex: pack hunting, colony safety)