Ecology and Population Biology: Study Notes

Animal Behavior

Overview of Animal Behavior

Animal behavior encompasses all the ways animals interact with other members of their species, other species, and their environment. Behaviors can be innate or learned, and are often responses to environmental stimuli.

• Behavior: Any change in activity of an organism in response to a stimulus.

• Innate behavior: Genetically hardwired, inherited behaviors (e.g., reflex actions).

• Learned behavior: Acquired over an organism's lifetime through experience.

Types of Learned Behavior

• Imprinting: Learning that occurs at a specific life stage and is often irreversible.

• Classical conditioning: Learning by associating a stimulus with a consequence (e.g., Pavlov's dogs).

• Operant conditioning: Learning based on rewards or punishments.

• Migration: Periodic movement in response to environmental cues, often involving learned and innate components.

Biological Rhythms and Behavior

• Circadian rhythm: Daily cycles of behavior and physiology.

• Biological clock: Internal mechanism that controls biological rhythms.

Questions in Behavioral Biology

• Causation: What causes the behavior?

• Development: How does the behavior develop?

• Function: How does the behavior affect fitness?

• Phylogeny: How did the behavior evolve?

Homeostasis

Maintaining Internal Stability

Homeostasis is the process by which organisms maintain a stable internal environment, balancing factors such as nutrients, water, temperature, and immune response.

• Involves four interacting components: stimulus, sensor, effector, and response.

• Requires cells to communicate to maintain balance.

Feedback Loops

• Negative feedback: Brings a variable back to normal (e.g., thermoregulation).

• Positive feedback: Intensifies or exaggerates the stimulus (e.g., childbirth).

Ecology: Biotic and Abiotic Factors

Biotic vs. Abiotic Factors

Ecological systems are influenced by both living (biotic) and nonliving (abiotic) factors. These factors interact within ecosystems to shape the environment and the organisms within it.

• Biotic: Living components (e.g., plants, animals, bacteria).

• Abiotic: Nonliving components (e.g., temperature, water, sunlight).

Hierarchical Organization of Ecology

• Organism → Population → Community → Ecosystem → Biome → Biosphere

Types of Biomes

• Tundra

• Taiga

• Temperate Forest

• Grassland

• Desert

• Savannah

• Tropical Rainforest

• Marine

Population Ecology

Population Density, Dispersion, and Demographics

Population density is the number of individuals per unit area or volume. Dispersion refers to the pattern of spacing among individuals within the boundaries of the population.

• Dispersion patterns: Clumped, uniform, and random.

• Demography: Study of birth rates, death rates, immigration, and emigration.

Pattern	Description
Clumped	Individuals aggregate in patches, often due to resource availability or social behavior.
Uniform	Individuals are evenly spaced, often due to territoriality or competition.
Random	Position of each individual is independent of others; rare in nature.

Population Growth Models

Exponential Growth

Describes population growth in an ideal, unlimited environment. The exponential growth equation is:

$\frac{dN}{dt} = rN$

• N: Population size

• r: Intrinsic rate of increase

Logistic Growth

Describes how a population grows more slowly as it nears its carrying capacity (K), the maximum population size the environment can support. The logistic growth equation is:

$\frac{dN}{dt} = rN \left( \frac{K-N}{K} \right)$

• Growth slows as N approaches K.

Life History Traits and Natural Selection

Life history traits are evolutionary outcomes reflected in development, physiology, and behavior. Organisms may be semelparous (single reproductive event) or iteroparous (multiple reproductive events).

• r-selection: Rapid reproduction, low survival rate.

• K-selection: Fewer offspring, high parental investment, higher survival rate.

Density-Dependent and Density-Independent Factors

• Density-dependent factors: Birth and death rates change with population density (e.g., competition, disease).

• Density-independent factors: Affect population regardless of density (e.g., weather, natural disasters).

Human Population Growth

The human population is no longer growing exponentially but is still increasing rapidly. Differences in growth rates are due to variations in birth rates, death rates, and ecological footprints among countries.

• Ecological footprint: The aggregate land and water area required to produce resources and absorb wastes for a population.

Community Ecology

Species Interactions

Species interactions can help, harm, or have no effect on the individuals involved. Major types include competition, exploitation, and positive interactions.

Interaction	Description
Competition (−/−)	Individuals of different species use a limited resource, reducing survival or reproduction of both.
Exploitation (predation, herbivory, parasitism) (+/−)	One species benefits, the other is harmed.
Mutualism (+/+)	Both species benefit.
Commensalism (+/0)	One species benefits, the other is unaffected.

• Competitive exclusion: Two species competing for the same resource cannot coexist permanently in the same place.

• Resource partitioning: Differentiation of ecological niches enables similar species to coexist.

Diversity and Trophic Structure

Biological communities are characterized by species diversity and trophic structure (feeding relationships). Food chains and food webs illustrate these relationships.

Ecosystem Ecology

Energy Flow and Chemical Cycling

Physical laws govern energy flow and chemical cycling in ecosystems. Energy flows through ecosystems in one direction, while nutrients cycle within them.

• Primary production: The amount of light energy converted to chemical energy by autotrophs.

• Limiting factors: Energy and other abiotic factors can limit primary production.

Biogeochemical Cycles

Biological and geochemical processes cycle nutrients and water in ecosystems. Major cycles include the water, carbon, nitrogen, and phosphorus cycles.

Restoration Ecology

Restoration ecologists aim to return degraded ecosystems to a more natural state by reestablishing native species, restoring nutrient cycles, and removing invasive species.