Lecture 14 Notes: Populations

Populations

• Population: Refers to a group of individuals of the same species residing in a specific geographic area and capable of interbreeding.

Population Dynamics

• Fluctuations in Populations:

  • Short-term Factors:

  • Weather events (e.g., storms, temperature fluctuations)

  • Diseases that affect survival rates

  • Availability of food supply impacting reproductive success

  • Long-term Factors:

  • Species introductions (invasive species, predation effects)

Species Examples

• Great Tits: Populations measured in pairs per hectare, with observations recorded over years indicating population trends.

  • Example data shows varying pairs per hectare from 0.4 to 3.6 over multiple years.

• House Finches: Data on birds sighted per hour shows population trends across different years, indicating fluctuations in presence and activity.

• Cattle Egrets: Tracking number of birds per party hour over years highlights colonization patterns in North America.

Population Growth

• Growth Curves:

  • Geometric Growth: Reflects rapid growth under ideal conditions.

  • Logistic Growth: Accounts for resource limitations and stabilizes as population reaches carrying capacity.

• Growth Potentials:

  • Large-bodied species (low reproductive rates): growth rates between 10-30%.

  • Small-bodied species (high reproductive rates): growth rates between 50-100%.

Population Control Mechanisms

• Limitation: Any factors that impose a ceiling on population growth, including:

  • Habitat availability

  • Food resources

  • Climate conditions

  • Disease and predation effects

• Regulation: The influence of population density on population size, as greater density can lead to increased competition and stress, thereby impacting growth.

Key Factors in Population Limitation

• Habitat:

  • Availability of suitable habitat is crucial for population survival; example includes the red-cockaded woodpecker requiring specific nesting sites.

• Food Supply:

  • Food availability can vary significantly from year to year, influenced by climatic conditions, leading to mass starvation in certain years, as seen in owl irruption events.

• Natural Enemies:

  • Predators, parasites, and diseases play significant roles in controlling populations.

  • Example of bird parasites includes:

  • Intestinal worms

  • Blood parasites

  • External parasites like ticks, lice, and introduced species such as blowflies in Galapagos affecting native species like Darwin's finches.

Social Forces in Population Regulation

• Territoriality: Social behaviors that determine the size of territories occupied by breeding pairs. Examples include:

  • Stages of settlement within habitats (initial colonization to established territories).

  • The balance between primary and secondary habitat use, influenced by population densities and resource availability.