Lecture 10: Populations: Growth Potential, Limits, Dynamics & Life History

Vocabulary practice flashcards covering population growth models, density-dependent regulation, Allee effects, life history strategies, and reproductive trade-offs from Lecture 10.

Density-independent factors

Environmental factors that affect population growth rate and mortality regardless of population size or density, such as droughts, fires, and flooding.

Negative density-dependent factors

Factors negatively affecting population growth that exert increasing strength as population size increases, causing populations to become self-limiting through reduced resource availability, lowered fecundity, conflict, disease, and elevated predation.

Carrying capacity ($K$)

The maximum population size of a species that a given environment can sustainably support, representing the point where population growth rate falls to zero.

Inflection point

The point of fastest growth on a logistic growth curve ($N = \frac{K}{2}$) that separates the early accelerating phase from the later decelerating phase, where the addition of new members no longer outweighs density-dependent factors.

Logistic growth model

A mathematical model formalizing the relationship between increasing population size and decreasing growth rate as carrying capacity is approached, expressed as $\frac{dN}{dt} = rN\left(1 - \frac{N}{K}\right)$.

Exponential growth model

A continuous population growth model describing growth under unlimited resources, expressed as $N_t = N_0 e^{rt}$, where $r$ is the intrinsic growth rate.

Geometric growth model

A discrete-time population growth model represented by $N_t = N_0 \lambda^t$, where $\lambda$ represents the discrete population growth multiplier per time step.

Self-thinning

A density-dependent process in plant populations where the negative effects of high density cause progressive mortality of individuals, allowing the surviving plants to increase in average individual biomass.

Positive density dependence

A relationship where population growth rate increases with increasing population size or density, often observed at low population numbers.

Allee effect

A phenomenon where beneficial social interactions at larger group sizes (e.g., finding mates, group foraging, and antipredator vigilance) increase individual fitness, causing populations below a critical minimum threshold to suffer reduced growth or sudden collapse.

Life history

The schedule of an organism's growth, development, reproduction, and longevity, shaped by adaptations allocating limited time and energy to maximize fitness.

Fast life history

A suite of life history traits characterized by a shorter life span, faster growth rate, earlier sexual maturation, earlier reproduction, high offspring count, and minimal parental investment.

Slow life history

A suite of life history traits characterized by a longer life span, slower growth rate, delayed sexual maturation, delayed reproduction, few offspring, and substantial parental investment.

Type I survivorship curve

A survivorship pattern characterized by high survival throughout juvenile and adult life stages, followed by high mortality primarily in old age (e.g., large mammals such as bears).

Type II survivorship curve

A survivorship pattern with a constant per capita probability of mortality throughout the organism's entire life span (e.g., squirrels and many birds).

Type III survivorship curve

A survivorship pattern characterized by extremely high mortality among offspring and young juveniles, with high survival rates for the few individuals reaching maturity (e.g., dandelions and many plants/marine invertebrates).

Grime's triangle

A plant life history framework that classifies species into competitors, stress tolerators, and ruderals based on the evolutionary trade-offs among competition, abiotic stress, and disturbance.

Stress tolerators

Plants adapted to high abiotic stress and low disturbance characterized by slow potential growth rates, late sexual maturity, low energy investment in seeds, and frequently important vegetative reproduction (e.g., wooly lousewort).

Competitors (Grime's triangle)

Plants adapted to environments with low abiotic stress and low disturbance characterized by rapid potential growth, early sexual maturity, low energy investment in seeds, and often important vegetative reproduction (e.g., goldenrod).

Ruderals

Plants adapted to high disturbance and low abiotic stress characterized by fast potential growth rates, early sexual maturity, a high proportion of energy devoted to seed production, and rarely important vegetative reproduction (e.g., Canada thistle).

Complex life cycle

A life cycle in which an organism undergoes dramatic morphological, physiological, or habitat transitions between developmental stages, such as distinct larval, pupal, and adult forms.

Semelparity

A reproductive strategy where an individual undergoes a single reproductive event in its entire lifetime before dying (e.g., periodical cicadas, bamboo, agave, and Pacific salmon).

Iteroparity

A reproductive strategy where an organism undergoes multiple reproductive episodes distributed across its lifespan (e.g., elephants, songbirds, frogs, and reptiles).

Senescence

A physiological decline characterized by a gradual decrease in fecundity paired with an increasing probability of mortality over the course of an organism's life.

Principle of allocation

The evolutionary and ecological principle stating that energy, nutrients, or time devoted to one structure, physiological function, or behavior cannot be simultaneously allocated to another.