Population Ecology Overview

Population Ecology

• Population is a group of individuals of the same species living in a particular area at the same time.
• Population Ecology focuses on understanding how populations grow, shrink, and interact with their environment.
• Levels of complexity in ecology: Individual/Organism, Population, Community, Ecosystem, Biosphere.
• Basic population characteristics include:
  • Population size (N) - total number of individuals in a population.
  • Population density - number of individuals per unit area, indicating if a species is rare or abundant.
  • Population distribution - how individuals are spaced relative to each other:
    • Random - no pattern (trees in a forest).
    • Uniform - fairly even spacing (nesting birds).
    • Clumped - individuals gather together (schooling fish).
  • Population sex ratio - ratio of males to females, usually 50:50, crucial for population growth.
  • Population age structure - number of individuals in each age category, determining if a population is increasing (large number of young) or decreasing (large number of old).

Factors Influencing Population Size

• Density-dependent factors affect survival based on population size:
  • Limiting resources like food influence an individual's odds of survival based on population size.
  • Carrying capacity is the maximum population an ecosystem can support due to resource availability.
• Density-independent factors have the same effect regardless of population size:
  • Natural disasters like tornadoes can impact survival irrespective of population size.

Population Growth Models

• Exponential growth model - ideal conditions with unlimited resources, resulting in a J-shaped curve.
  • Intrinsic growth rate is the maximum growth rate for a species under ideal conditions.
• Logistic growth model - considers environmental limits on growth, resulting in an S-shaped curve.
  • Carrying capacity limits growth as resources become scarce.

Reproductive Strategies

• K-selected species have:
  • Low intrinsic growth rate.
  • Slow population growth.
  • Large body size.
  • Late maturity.
  • Few offspring.
  • Substantial parental care.
• r-selected species have:
  • High intrinsic growth rate.
  • Fast population growth.
  • Small body size.
  • Early maturity.
  • Many offspring.
  • Little or no parental care.

Survivorship Curves

• Type I - high survival throughout life (K-selected species: humans, elephants).
• Type III - low survival early in life, few reach adulthood (r-selected species: mosquitoes, dandelions).
• Type II - constant decline in survivorship throughout life (squirrels, coral).

Metapopulations

• Metapopulations are fragmented parts of a larger population.
• Movement between metapopulations reduces extinction risk by increasing genetic diversity and population size.

Community Ecology

• Community - all populations of different species living together in a particular area.
• Community Ecology studies the organization and functioning of communities and their interactions.

Interspecific Interactions

• Competition (-/-) - two species compete for a limited resource.
• Exploitation (+/-) - one species benefits by consuming another:
  • Predation - predator kills and eats prey.
  • Herbivory - herbivore eats part of a plant.
  • Parasitism - parasite derives nourishment from its host.
• Positive Interactions (+/+ or 0/+) - one species benefits, while the other either benefits or is not harmed:
  • Mutualism (+/+) - both species benefit.
  • Commensalism (+/0) - one species benefits, the other is unaffected.

Competition

• Competitive exclusion principal - two species competing for the same limiting resource cannot coexist.
• Resource partitioning - two species divide the resource based on behavior or morphology, leading to evolution:
  • Temporal resource partitioning - using the same resource at different times.
  • Spatial resource partitioning - using different locations.
  • Morphological resource partitioning - evolving different body plans to use different parts of the resource.

Mutualism

• Mutualism - two species interact to increase survivability for both.
  • Examples: Plants and pollinating insects, acacia trees and ants.

Commensalism

• Commensalism - one species benefits while the other is not affected.
  • Examples: Birds nesting in trees.

Keystone Species

• Keystone species are vital for ecosystem stability, their removal leads to instability.
  • Examples:
    • Food supply species.
    • Predator-mediated competition - predators control populations of superior competitors.
    • Ecosystem engineers - create habitat for other species.

Changes in Communities over Time

• Ecological succession - predictable replacement of one group of species by another.
  • Primary succession - occurs on surfaces without soil, like new volcanic areas.
  • Secondary succession - occurs in disturbed areas with soil, like after a fire.
  • Pioneer species - early colonists that grow rapidly and need lots of sunlight.
  • Climax community - the later stages of succession, considered the typical community for that biome.

Species Diversity

• Species diversity is the variety of species in a community, with two components:
  • Species richness - the number of different species.
  • Relative abundance - the total number of individuals of a species relative to the total number of individuals of all species.
• Shannon diversity index (H) is a widely used tool to measure species diversity, with higher values indicating higher diversity.

Explore the fundamentals of population ecology, focusing on how populations grow, shrink, and interact with their environment. Learn about key characteristics such as population size, density, distribution, and sex ratio. This quiz provides insights into the complexity of ecological levels from individuals to ecosystems.