Population Growth

Ecologists use various tools to understand population change. Growth occurs when resources are abundant but is ultimately limited by resource availability.
Populations are dynamic, responding to biotic and abiotic factors, with insights derived from modeling and observation.

Definition: Applies to organisms with one reproductive event per year (discrete reproduction), such as plants, elk, and caribou.
Assumptions: Unlimited resources and negligible predation.

Definition: Characterized by overlapping generations with unlimited resources.
Intrinsic Growth Rate (r): Growth rate per individual under unlimited resources.
Maximum Intrinsic Growth Rate (r_max): Highest possible growth rate for a species under optimal conditions.
Per Capita Growth Rate: Rate of new individuals added per existing individual.
Doubling Time: Time for a population to double in size.
Observations: Seen in exotic invasive species and human population growth, raising sustainability questions.

Definition: Growth rate changes with population density, with the fastest growth in the middle phases.
Carrying Capacity (K): The maximum sustainable population size an environment can support, limited by factors like space, nutrients, food, and water.

Definition: Biotic factors whose effects on population growth vary with population density (e.g., disease, resource competition).

Definition: Abiotic factors affecting population dynamics regardless of density (e.g., natural disasters, weather).

Population fluctuations are closely linked to rainfall, showing dramatic drops during droughts and recovery during rainy periods.

Recognizes interconnected populations, not isolated units.
Climate change influences dispersal patterns, as seen in historical northward spread of species like maple and hemlock.

Habitat patches may go extinct but persist through immigration from other patches.
Key variables include patch size, relation to other patches, and immigration/emigration rates.

A collection of spatially distinct subpopulations of the same species connected via dispersal, allowing the whole system to persist despite individual extinctions.

Random variability in environmental factors (e.g., resources, weather) affecting population growth rates.

Variability in birth and death rates, with chance events having larger impacts on smaller populations.

Observations of cyclic population overshoots of carrying capacity (e.g., lemmings, Fire Island deer).

Mule deer population fluctuated significantly due to changes in predator populations managed by human policies, demonstrating overshooting and drastic declines.