Populations and Communities

Ecology: Study of processes influencing organism distribution/abundance and interactions between living things/environment.
Species: Group of individuals with shared characteristics, reproductively isolated.
Population: Interbreeding group of a species in an area.
Biotic Community: Grouping of populations (vegetation, animals, microorganisms) in an area, determined by abiotic factors (e.g., water, climate, soil).
Ecosystem: Interactive complex of biotic communities and abiotic factors (e.g., forests, coral reefs).
Ecotone: Transitional region between ecosystems, sharing species and characteristics.
Biome: Large terrestrial area with similar climate and vegetation, predicted by rainfall and temperature.
Biosphere: System formed by all living things.

Conditions: Factors varying in space/time but not used up (e.g., temperature, pH).
Resources: Factors consumed by organisms (e.g., water, food, light).
Optimal Range: Environmental level where organisms thrive best.
Range of Tolerance: Entire range allowing any growth.
Limits of Tolerance: High and low ends of the range.
Zones of Stress: Between optimal range and limits of tolerance.
Law of Limiting Factors: Any factor outside the optimal range limits growth, reproduction, and survival; can be too much or too little.
Synergistic Effects: Factors interacting to cause a greater combined effect.

Habitat: Place a species is adapted to live, defined by vegetation and physical environment.
Niche: All environmental components an organism interacts with (food, shelter, abiotic factors).
Species coexist in a habitat but occupy separate niches to reduce competition.

Population Change: (Births + Immigration) - (Deaths + Emigration) = Change in population number
Population Growth Rate (r): Number of offspring individuals produce per unit time with unlimited resources.
Equilibrium: (Births + Immigration) = (Deaths + Emigration).
Constant Growth: Population adds constant number of individuals over time (linear growth, not typical in nature).
Exponential Growth: Growth at a constant rate of increase (J-curve), assumes unlimited resources, leads to population explosion and eventual crash.
Carrying Capacity (K): Maximum population a habitat can support without being degraded.
Logistic Growth: Growth that levels off near carrying capacity (S-curve), growth rate slows as population approaches K.
Critical Number: Minimum number of individuals allowing survival and recovery of a population; below this, extinction is almost inevitable.

Biotic Potential: Number of offspring produced under ideal conditions, measured by r.
Recruitment: Survival of young to become part of the breeding population.
Environmental Resistance: Biotic and abiotic factors limiting population increase (e.g., predators, disease, lack of food, extreme weather).
Population Density: Number of individuals per unit area.
Density-Dependent Factors: Impact intensifies with increasing population density (e.g., disease, predation, food shortages).
Density-Independent Factors: Effects are independent of population density (e.g., fire, flood, pollution).
Top-down Regulation: Population control by predation.
Bottom-up Regulation: Population control by resource scarcity.

r-strategists (r-selected species): High biotic potential, rapid reproduction, short lifespan, low recruitment, adaptable to changing environments (e.g., housefly, dandelion).
K-strategists (K-selected species): Lower biotic potential, care for young, live in stable environments, populations fluctuate around K (e.g., elephant, California condor).

Predation (+--interaction): One benefits (predator) and the other is harmed (prey); includes parasitism (feeds without often killing host) and pathogenicity (disease-causing agents).
Competition (---interaction): Both species are harmed from competing for scarce resources.
- Interspecific: Between different species.
- Intraspecific: Between members of the same species.
- Competitive Exclusion Principle: Species cannot survive if they compete directly for the same resources.
- Resource Partitioning: Division and specialization of a resource to limit competition.
- Territoriality: Defense of an area by an individual or group, reducing density-dependent limitations.
Mutualism (++-interaction): Both species benefit (e.g., pollinators and plants).
Commensalism (+0-interaction): One species benefits, the other is unaffected (e.g., barnacles on whales).
Amensalism (0--interaction): One species is harmed, the other is unaffected (e.g., black walnut chemical toxicity).
Symbiosis: Close, long-term interaction between two different species.
Invasive Species: Non-endemic species introduced to an ecosystem that outcompete natives due to lack of natural predators.
Keystone Species: Play a crucial role in maintaining ecosystem biotic structure, preventing other species from dominating (e.g., sea otters).

Selective Pressures: Environmental resistance factors affecting survival and reproduction (e.g., predators, drought).
Natural Selection: Process where genetic traits favor survival of certain individuals.
Biological Evolution: Modification of a species' gene pool by natural selection over generations.
Adaptation: Genetic traits or features that aid an organism in survival and reproduction.
Species facing new pressure can adapt, migrate, or go extinct.
Genetic Variation: Occurs by mutation and crossover, essential for adaptation.
Four Variables Affecting Survival: Geographical distribution, specialization, genetic variation, reproductive rate (r) relative to environmental change.

Speciation: Formation of new species by modification of existing ones, requires reproductive isolation of populations.
Geographic Isolation: Populations separated by physical barriers, leading to different selective pressures and genetic divergence (e.g., plate tectonics).