Population Ecology and Community Ecology: Key Concepts and Definitions (Chapters 53 & 54)

Study Guide - Smart Notes

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Population: A group of individuals of the same species that live in the same area and interbreed, producing fertile offspring.
Populations are characterized by their size, density, distribution, age structure, and reproductive rates.

Survivorship Curve: A graphical representation showing the number or proportion of individuals surviving at each age for a given species or group.
There are three main types:
- Type I: High survivorship during early and middle life, followed by a rapid decline in survivorship in later life (e.g., humans, large mammals). Underlying reason: Parental care and low offspring number.
- Type II: Constant death rate over the organism's life span (e.g., birds, some reptiles). Underlying reason: Equal chance of death at any age.
- Type III: High death rates for the young, with a few individuals surviving to older age (e.g., oysters, many fish, plants). Underlying reason: Large number of offspring, little or no parental care.

Exponential Growth: Population increase under ideal conditions, resulting in a J-shaped curve. No limiting factors are present.
Logistic Growth: Population growth that slows as it approaches the carrying capacity (K) of the environment, resulting in an S-shaped curve.

Exponential Growth Equation:

Logistic Growth Equation:

r-selection: Selection for traits that maximize reproductive success in uncrowded environments (high growth rate, many offspring, little parental care).
K-selection: Selection for traits that are sensitive to population density and favored at high densities (few offspring, high parental care, competitive ability).
Contrast: r-selected species thrive in unstable environments; K-selected species thrive in stable environments near carrying capacity.

Density-dependent factors: Factors whose effects on population size increase or decrease depending on population density (e.g., competition, predation, disease).
Density-independent factors: Factors that affect population size regardless of density (e.g., weather, natural disasters).

Human populations have shown exponential growth, but growth rates are declining in many regions due to demographic transition.
Demographic Transition: The shift from high birth and death rates to low birth and death rates, typically associated with industrialization and improved living conditions.
Age Structure: The distribution of individuals among different ages in a population, often depicted as an age pyramid.
Demographic Inertia: The continued growth of a population after fertility rates have declined, due to a large proportion of individuals in reproductive age.

Ecological Niche: The sum of a species' use of the biotic and abiotic resources in its environment; its "ecological role."

Competition: Interaction between organisms or species for limited resources, negatively affecting both parties.
Competitive Exclusion Principle: Two species competing for the same limiting resource cannot coexist permanently; one will outcompete the other.
Character Displacement: The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations, due to competition.
Asymmetric Competition: Competition in which one species suffers a much greater fitness decline than the other.

Predation (Exploitation): An interaction in which one organism (the predator) kills and eats another (the prey).
Examples: Lions hunting zebras, birds eating insects.
Predator/Prey Coevolution: Reciprocal evolutionary adaptations in predator and prey (e.g., camouflage in prey, improved senses in predators).

Symbiosis: An intimate relationship between two or more species that live in direct contact with one another.
Mutualism: A symbiotic relationship in which both species benefit (e.g., bees and flowering plants, mycorrhizal fungi and plant roots).

Commensalism: A symbiotic relationship in which one species benefits and the other is neither helped nor harmed (e.g., barnacles on whales).

Logic: Measures the probability that two individuals randomly selected from a sample will belong to the same species.

Simpson's Index Equation:

Food Chain: A linear sequence of organisms through which nutrients and energy pass as one organism eats another.
Food Web: A complex network of interconnected food chains in an ecosystem.

Keystone Species: A species that has a disproportionately large effect on its environment relative to its abundance (e.g., sea otters).
Dominant Species: Species that are most abundant or have the highest biomass in a community.
Difference: Keystone species maintain community structure; dominant species are simply the most numerous or massive.

Bottom-up Model: Community structure is controlled by the availability of nutrients and resources at lower trophic levels.
Top-down Model (Trophic Cascade): Community structure is controlled by predation from higher trophic levels.

Term	Definition
Conversion Efficiency	The percentage of energy transferred from one trophic level to the next.
Trophic Cascade	Indirect effects in a community that are initiated by a predator.
Primary Consumers	Herbivores that eat primary producers (plants and algae).
Secondary Consumers	Carnivores that eat primary consumers.
Tertiary Consumers	Carnivores that eat other carnivores (secondary consumers).

Additional info: Some examples and explanations were expanded for clarity and completeness based on standard biology textbooks.