Population Ecology Overview

Population Ecology

• Population ecology is the study of populations in relation to their environment
• It encompasses environmental influences on population density and distribution, age and structure, and variations in population size.

Characteristics of Population

• Population size: The total number of individuals in a population
• Population density: The number of individuals per unit area or volume
• Dispersion patterns: The arrangement of individuals in a population (clumped, uniform, random).
• Demographics: The study of vital statistics of a population and how they change over time. This includes age structure and sex ratios.
• Survivorship curves: Graphs showing the proportion of individuals surviving at each age for a species or group. There are three types (Type I, II, III).
• Population growth: The rate at which the number of individuals in a population increases or decreases over time.

Population Size

• Population size (N): The number of individual organisms in a population.
• Factors governing population size
  • Crude Birth Rate (CBR): Ratio of total live births to total population in a particular area over a specified period of time.
  • Crude Death Rate (CDR): Ratio of the total number of deaths to total population.
  • Immigration: The number of organisms moving into an area.
  • Emigration: The number of organisms moving out of an area.

Population Density

• Measurement of the number of people in an area, an average number.
• Usually shown as the number of people per square kilometer.
• Density = Population/area
• Methods of measuring population density include:
  • Total count method: Direct counting of population; useful for few organisms or easily visible organisms. Examples include breeding colonies.
  • Sampling method: Used when it is not possible to count all individuals, depends on the species and its distribution. Examples include plot-based or quadrant methods, and capture-recapture methods.

Population Dispersion

• Pattern of spacing among individuals within geographic boundaries, including clumped, random, uniform dispersion.

Clumped Dispersion

• Individuals are aggregated in patches.
• Common in many animal groups due to resource availability, social behavior.
• It is the most frequent pattern of species distribution.

Uniform Dispersion

• Evenly spaced distributions, individuals maintain a minimum distance from each other.
• Can occur due to competition for resources or territoriality.

Random Dispersion

• Spacing pattern based on unpredictability, least common.
• Occurs when individuals have no strong attraction or repulsion to others.
• Example: Dandelions and windblown seeds.

Factors Affecting Distribution

• Density-independent factors: Factors that affect a population's size regardless of the population density (floods, hurricanes, fires, weather, clear cutting).
• Density-dependent factors: Factors that affect a population's size in relation to the population's density (competition, predation, parasitism, disease).

Demography

• Study of vital statistics of populations and how they change over time, including age structure and sex ratio.

Age Structure

• Describes the number of individuals in each age class, and their ratio to other age classes. Often displayed as a population pyramid.
• Includes Prereproductive, Reproductive, Post-reproductive categories.

Life Table

• A table showing the probability of survival for each age class.
• Provides data on survival rates from one age to the next age.
• Used to predict lifespan of organisms.

Survivorship Curve

• Graph showing the proportion of surviving individuals at each age for a given species or group (Males & Females).
• Based on a life table, for a given cohort (same age group).
• Three types:
  • Type I: Late loss (high survivorship until late in life). Animals like humans are frequently in this category, and have high parental care.
  • Type II: Constant loss (survival rate is independent of age). Animals like birds tend to display this pattern.
  • Type III: Early loss (high mortality early in life). Trees and oysters tend to fall into this category.

Population Growth

• Refers to the number of individuals in a population increasing or decreasing over time.
• Controlled by birth rate and death rate, immigration and emigration.
  • Exponential growth: Unrestricted growth; the growth rate accelerates exponentially over time.
  • Logistic growth: Restricted growth; growth rate of the population slows down as it reaches the carrying capacity.
• Carrying Capacity: The maximum density of a population that the environment can support over a sustained period without damage.
  • When a population exceeds its carrying capacity, it can crash.

Species Interaction

• Direct or indirect interrelationship or association between different living organisms (plants, plants, animals, animals, or with microorganisms).
  • Competition(-,-): When organisms or species compete for limited resources (e.g., food, space, mates).
  • Predation(+,-): When one species (predator) consumes another (prey).
  • Parasitism (+,-): When one species (parasite) benefits and the other (host) is harmed.
  • Commensalism (+,0): When one species benefits and the other is neither harmed nor helped.
  • Mutualism (+,+): When both species benefit.
  • Amensalism(-,0): When one species is harmed, and the other is unaffected.

Coevolution

• The influence interactions between species have on population densities and gene frequencies.
• Predator-prey coevolution: Prey evolve defenses, predators evolve more effective hunting strategies
• Mutualistic coevolution: Species evolve adaptations that benefit both. (examples are pollinators and flowering plants).

This quiz explores the fundamental concepts of population ecology, including population size, density, demographics, and growth patterns. Test your knowledge on the various characteristics that define populations and their interactions with the environment.