Population Ecology Flashcards

Introduction to Population Ecology

Population ecology is the branch of ecology that studies groups of individuals of the same species living in the same area at the same time. This field explores the dynamics of population size, distribution, and structure, and how these factors interact with one another within the environment.

Geographical Distribution of Populations

Populations can be distributed in various ways across geographic spaces. The global range refers to the total area inhabited by a species globally, for example, the population of Zootoca vivipara has specific ranges across Europe and Asia.

Populations can exhibit different patterns of distribution:

• Uniform Dispersion: Individuals are evenly spaced across the environment, often due to territorial behavior.

• Random Dispersion: Individuals are distributed randomly, with no specific pattern; this typically occurs when resources are plentiful and uniformly dispersed.

• Clumped Dispersion: Individuals are grouped together, often around resources or for social interactions.

Survivorship Curves

Survivorship curves are graphical representations illustrating how the number of individuals in a population changes over time, showing different survival rates across age classes:

1. Type I: Characterized by high survivorship throughout life, with most individuals living to the maximum age (e.g., humans).

2. Type II: Survivorship is relatively constant throughout life, showing a steady decline in numbers (e.g., birds).

3. Type III: High mortality rates early in life, with few survivors reaching maturity (e.g., many fish species).

For instance, crocodilians experience high mortality rates at young ages, with very few reaching large sizes. Those that do often survive to the species' maximum lifespan, exemplifying the Type III survivorship curve.

Population Dynamics

The dynamics of populations include the factors that regulate changes in population size. This includes understanding how to predict issues like overpopulation, identifying endangered species, and monitoring invasive species.

• The Net Reproductive Rate (R0) is crucial for understanding population dynamics, indicating the average number of female offspring produced by each female across her lifetime. If R0 > 1, the population is increasing, while R0 < 1 signifies a decreasing population.

Fitness Trade-Offs

Fitness trade-offs occur because individuals have limited time and energy resources. One notable trade-off seen in many species involves balancing reproductive output (e.g., clutch size) with survival rates. These trade-offs shape life history strategies and influence population dynamics.

Population Growth

Population growth can be quantified as the change in population size ($\Delta N$) per unit time ($\Delta t$). The formula is:
Δ⁢N/Δ⁢t=Births−Deaths+Immigrants−Emigrants
In absence of migration, it simplifies to:
Δ⁢N/Δ⁢t=Births−Deaths
The per capita growth rate formula is:
Population growth rate(Δ⁢N/Δ⁢t)=r×N
where $r$ is the per-capita rate of increase and varies based on birth and death rates. A population grows when births exceed deaths.

Intrinsic Growth Rate

The intrinsic growth rate ($r{max}$) describes a population's growth potential under ideal conditions, reflecting maximum birth rates and minimal death rates. Species with rapid maturation and high offspring production exhibit a high $r{max}$, while those with slower maturation rates have lower $r_{max}$.

Exponential vs. Logistic Growth

Exponential growth occurs when a population grows at a rate proportional to its current size (high $r$ and/or $N$), and resources are not limiting. This growth cannot continue indefinitely due to environmental constraints. The growth of populations typically follows a logistic model when they approach the carrying capacity (K) of the environment.

Carrying Capacity and Population Limiting Factors

Carrying capacity is the maximum number of individuals an environment can sustain, influenced by both density-dependent and density-independent factors. Density-dependent factors, such as disease and competition, affect population size based on population density. Conversely, density-independent factors, like weather or catastrophic events, impact populations regardless of their density.

Habitat Fragmentation

Habitat fragmentation can increase isolation among populations, potentially reducing their sizes and genetic diversity. In fragmented habitats, populations may become metapopulations, where each subpopulation can go extinct but can be repopulated through migration.

Conclusion and Learning Objectives

To summarize, understanding population ecology involves calculating growth rates, predicting population dynamics, and recognizing the ecological and biological factors that drive population cycles. Key learning objectives include:

• Describing geographical distribution of populations.

• Understanding survivorship curves and their implications.

• Analyzing trade-offs between survivorship and fecundity.

• Exploring age structure influences on population growth.