Population Ecology Concepts

Population Ecology

• Populations are groups of individuals of the same species in a given area.
• Population size is affected by birth rates, death rates, immigration, and emigration.
• Factors influencing population growth include biotic potential (the maximum rate at which a population could increase under ideal conditions) and environmental resistance (all factors that limit population growth).
• Exponential growth occurs when a population increases by a fixed percentage each year, resulting in a J-shaped curve.
• Logistic growth occurs when a population's growth rate slows as it approaches its carrying capacity, resulting in an S-shaped curve.
• Carrying capacity is the maximum population size that a particular environment can sustainably support.
• Density-dependent factors affect a population's size in proportion to the population's density, including competition for resources, predation, and disease.
• Density-independent factors affect a population's size regardless of the population's density, including natural disasters (e.g., floods, hurricanes).
• Age structure diagrams (population pyramids) show the relative numbers of individuals at different ages in a population, helping predict future population trends.

Community Ecology

• A community is all the interacting populations in a given area.
• Interspecies competition occurs when resources are limited and two or more species compete for the same resources.
• Predation is an interaction where one species (predator) hunts and kills another species (prey).
• Symbiosis is a close ecological relationship where two or more species live together.
• Mutualism (+/+) is where both species benefit.
• Commensalism (+/0) is where one species benefits and the other is unaffected.
• Parasitism (+/-) is where one species benefits and the other is harmed.
• Ecological succession is the gradual process of change and replacement of species in a community over time.
• Primary succession begins in lifeless areas and proceeds slowly as soil forms.
• Secondary succession occurs in areas previously inhabited by living organisms.
• Keystone species are species that have a disproportionately large effect on their environment relative to their abundance. Their removal can have significant community-wide effects.
• Disturbances are events that impact communities (e.g., fires, floods, clear-cutting).

Ecosystems

• An ecosystem includes all the organisms in a given area along with the non-living (abiotic) factors such as water, sunlight, temperature, and minerals.
• Energy flow describes the movement of energy through an ecosystem.
• Producers (autotrophs) are at the base of the food web, capturing energy (usually from sunlight) and converting it into chemical energy (food).
• Consumers (heterotrophs) obtain energy by consuming other organisms; herbivores eat producers, carnivores eat other consumers, and omnivores eat both.
• Decomposers and detritivores break down dead organisms and return nutrients to the ecosystem.
• Trophic levels represent different feeding positions in an ecosystem.
• Food webs illustrate the complex feeding relationships between organisms in an ecosystem.
• Biogeochemical cycles involve the movement of nutrients through the biotic and abiotic parts of an ecosystem (e.g., water cycle, carbon cycle, nitrogen cycle).
• Biomes are large geographic areas with similar climates and dominant plant life. Tropical rainforests, deserts, and grasslands are examples.
• Conservation efforts aim to protect biodiversity and maintain ecosystem services that benefit humans.

Biosphere

• The biosphere encompasses all life on Earth and the environments where they live.
• Global ecology examines the interactions between organisms across large geographic scales.
• Global climate patterns and human activities impact biodiversity.
• Biodiversity is the variety of life at all levels, from genes to ecosystems.