Ecology, Behavioral Ecology, Population & Community Ecology, and Biodiversity: Study Guide

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Ecology: Introduction and Levels of Organization

Definition and Scope of Ecology

Ecology is the scientific study of interactions between organisms and their environment, encompassing both living (biotic) and non-living (abiotic) components. Ecologists investigate how these interactions shape the distribution and abundance of organisms.

Levels of Organization (from smallest to largest):
- Organism: Individual living entity (e.g., a single wolf).
- Population: Group of individuals of the same species in a given area (e.g., wolves in Yellowstone).
- Community: All populations of different species in an area (e.g., wolves, elk, trees in Yellowstone).
- Ecosystem: Community plus the abiotic environment (e.g., Yellowstone's biota and physical environment).
- Biosphere: All ecosystems on Earth.
Identifying Levels: For example, studying how wolves affect elk numbers is a community-level question; studying wolf pack size is a population-level question.

Biotic vs. Abiotic Factors

Biotic factors: Living components (e.g., plants, animals, bacteria).
Abiotic factors: Non-living components (e.g., temperature, water, sunlight, soil, nutrients).

Species Distribution and Influencing Factors

Species distributions are shaped by both past (e.g., glaciation, continental drift) and present (e.g., climate, competition) factors.
Barriers such as mountains, oceans, or human activity can limit distribution.

Niche Concept

Niche: The range of resources and conditions a species can use and tolerate.
Graphical representation: Niche graphs show resource use along environmental gradients.

Weather vs. Climate

Weather: Short-term atmospheric conditions (e.g., today's temperature, precipitation).
Climate: Long-term average weather patterns in a region.

Global and Regional Climate Patterns

Equator vs. Poles: The equator is warm due to direct sunlight; poles are cold due to low-angle sunlight.
Earth's Tilt and Seasons: The tilt of Earth's axis causes seasonal variation in sunlight intensity.
Regional Features: Mountains, oceans, and prevailing winds can create microclimates (e.g., rain shadows).

Biomes

Terrestrial Biomes: Defined by vegetation type and climate (e.g., tundra, desert, tropical rainforest).
Aquatic Biomes: Defined by physical factors such as salinity, depth, water flow (e.g., lakes, rivers, oceans).
Key differences: Terrestrial biomes are classified by plant communities; aquatic by physical/chemical factors.

Factors Affecting Aquatic Systems

Light: Penetration decreases with depth, affecting photosynthesis.
Depth: Influences temperature, pressure, and light availability.
Salinity: Varies between freshwater and marine systems.
Water Flow: Affects oxygen levels and nutrient distribution.
Nutrients: Availability limits productivity (e.g., nitrogen, phosphorus).

Behavioral Ecology

Definition and Control of Behavior

Behavior is any observable action or response of an organism to its environment. Behaviors are controlled by genetic and environmental factors and are shaped by natural selection to maximize fitness.

Proximate vs. Ultimate Causation

Proximate causation: Explains how a behavior occurs (mechanisms, physiology, development).
Ultimate causation: Explains why a behavior occurs (evolutionary significance, fitness benefits).

Innate vs. Learned Behaviors

Innate behaviors: Genetically programmed, present at birth (e.g., reflexes, fixed action patterns).
Learned behaviors: Acquired through experience (e.g., imprinting, conditioning).
Most behaviors exist on a spectrum between innate and learned.

Behavior and Fitness

Behaviors affect fitness by influencing survival and reproduction.
Trade-offs exist between costs (energy, risk) and benefits (food, mates).

Optimal Foraging Theory

Predicts that animals maximize energy gained per unit time spent foraging.
Formula:

Mating Systems and Parental Investment

Mating systems: Monogamy, polygamy, promiscuity.
Parental investment: The sex investing more in offspring is choosier; the other competes for access.

Sexual Selection

Intersexual selection: Mate choice (e.g., peahens choosing peacocks).
Intrasexual selection: Competition within a sex (e.g., male-male combat).

Altruism and Its Evolution

Altruism: Behavior that reduces an individual's fitness but increases another's.
Can evolve via kin selection (helping relatives) or reciprocal altruism (helping non-relatives with expectation of return).

Population and Community Ecology

Populations and Communities

Population: Group of individuals of the same species in an area.
Community: All populations of different species in an area.
Described by size, density, dispersion, and structure.

Population Size and Change

Population size changes via births, deaths, immigration, and emigration.
Population growth models:
- Exponential growth: Unlimited resources,
- Logistic growth: Limited resources,

Dispersion Patterns

Clumped: Individuals aggregate in patches (e.g., schools of fish).
Uniform: Evenly spaced (e.g., territorial birds).
Random: Unpredictable spacing (e.g., wind-dispersed plants).

Community Structure and Species Interactions

Community structure: Number and relative abundance of species, and their interactions.
Major types of species interactions:
- Competition: Both species harmed (-/-)
- Predation/Herbivory/Parasitism: One benefits, one harmed (+/-)
- Mutualism: Both benefit (+/+)
- Commensalism: One benefits, one unaffected (+/0)
Species reduce competition via resource partitioning or character displacement.
Predation drives adaptations such as camouflage, mimicry, and defensive behaviors.

Foundation vs. Keystone Species

Foundation species: Have large effects due to high abundance or biomass (e.g., trees in a forest).
Keystone species: Have disproportionate effects relative to abundance (e.g., sea otters).

Disturbance and Succession

Disturbance: Event that changes community structure (e.g., fire, flood).
Ecological succession: Sequence of community changes after disturbance.
Primary succession: Occurs on newly formed surfaces (no soil).
Secondary succession: Occurs where soil remains after disturbance.

Biodiversity and Conservation Biology

Biodiversity: Definition and Levels

Biodiversity: Variety of life at all levels of organization.
Three levels:
- Genetic diversity: Variation within species.
- Species diversity: Number and relative abundance of species.
- Ecosystem diversity: Variety of ecosystems.

Measuring Biodiversity

Measured by species richness, evenness, and genetic variation.

Importance of Genetic Diversity

Enables populations to adapt to changing environments and resist diseases.

Global Patterns of Biodiversity

Latitudinal gradient: Biodiversity highest at the equator, decreases toward poles.
Biodiversity hotspots: Areas with high species richness and endemism, under threat.

Importance of Biodiversity to Ecosystem Function

Enhances productivity, stability, and resilience of ecosystems.

Resistance vs. Resilience

Resistance: Ability to withstand disturbance.
Resilience: Ability to recover after disturbance.
Both contribute to ecosystem stability.

Threats to Biodiversity (HICOP)

Threat	Description	Example
Habitat loss	Destruction or fragmentation of habitats	Deforestation
Invasive species	Non-native species outcompete natives	Zebra mussels in US lakes
Climate change	Alters temperature and precipitation patterns	Coral bleaching
Overexploitation	Unsustainable harvesting of resources	Overfishing
Pollution	Contamination of air, water, soil	Pesticide runoff

Ecosystem Services

Provisioning: Food, water, timber.
Regulating: Climate regulation, flood control.
Supporting: Nutrient cycling, soil formation.
Cultural: Recreation, spiritual value.
Ecosystem services are vital for human well-being and have economic value.

Conservation Strategies

Protected areas (e.g., national parks).
Restoration ecology (e.g., reforestation).
Captive breeding and reintroduction.
Legislation (e.g., Endangered Species Act).