POPULATION ECOLOGY

Cards (34)

  • Population Ecology
    The study of populations in relationship to their environment and the social interactions amongst each other
  • Species
    A group of organisms capable of interbreeding, producing fertile offspring
  • Population
    A group of the same species that occupies the same habitat at the same time
  • Community
    Groups of different populations that interact with each other within a specific habitat
  • Ecosystem
    A community of interacting organisms and their physical environment
  • Population size is influenced by both abiotic and biotic factors factors present in the environment
    • Natality
    • Mortality
    • Immigration
    • Emigration
  • Causes of fluctuations in population size
    • Density dependant and independent factors contribute to fluctuations in population size
    • These factors increase environment resistance (pressure that suppress the population size)
    • Together these factors limit population growth
    • Environmental resistance includes carrying capacity, density dependant and independant factors
  • Carrying capacity
    The number of individuals of a particular population an environment can support in a specific season
  • Density dependant factors
    Factors that have a direct correlation to the size of the population in an area
    Exert a greater influence when a population is large
    Examples
    • Territorial behaviour
    • Predation and Competition
    • Accumulation of waste
    • Food,space, and shelter
    • Parasitism and disease
  • Density Independant Factors
    Factors that will exert an influence on a population regardless of its size
    Abnormal events in nature and occur randomly
    Examples
    • Tsunamis
    • Landslides
    • Volcanic eruptions
    • Veld fires
    • Floods
  • Geometric Growth
    Lag Phase
    • Population number increases slowly because individuals may still be acclimitising to their environment
    • Need time to fin mates
    • Most of the population is sexually immature
  • Geometric phase
    • Individuals have acclimatised
    • Many reproducing individuals exist and in favourable conditions produce many offspring
    • Birth rate is higher than death rate
    • Very little environmental resistance
  • Extinction
    • Resources become limited
    • Build up of toxic waste
    • Mortality rate becomes greater than the natality rate
    • Population decreases rapidly
  • Logistic Growth: found in higher-order organisms which typically reproduce slower
  • Lag phase
    • Growth is slow
    • Small number of reproducing individuals
    • Individuals need time to settle in and they become sexually mature
    • Population density is low - difficult to find a mate
  • Exponential phase
    • Population grows rapidly
    • More sexually mature individuals procreating
    • Little or no environmental resistance
    • Higher natality than mortality
  • Decelerating growth
    • Growth rate slows down
    • Environmental resistance develops
    • More competition for resources
    • Natality still higher than mortality
  • Equilibrium
    Population stabilzes
    Natality more or less equal to mortality
    Carrying capacity for the environmental has been reached
  • Death Phase
    • Sudden large drop in population size
    • Conditions have become unsuitable/external environmental change
  • Direct counting techniques
    • Aerial photography
    • Census
  • Indirect counting techniques
    • Mark and recapture
  • Ensure validity
    • Same method of marking
    • Same species
    • Same area
    • Same method of catching
  • Improve reliability
    • Repeat investigation
    • Increase sample size
    • Give sufficient time to remix after 1st capture
    • Make sure organisms do not become trap shy/addicted
    • Make sure the mark does not affect movement/behaviour
  • Simple sampling
    To ensure reliability
    • Several quadrat throws should be made to determine the average number of individuals per quadrant
    • Quadrat samples must be done randomly throughout the total area
    • The process should be repeated should be repeated several times and the average number of organisms per quadrat calculated
  • Competition: Interaction between individuals over scarce resources
    Intraspecific - When individuals of the same species compete
    Interspecific - Individuals of different species compete
  • Competitive exclusion - when two species competing for the same resources, one species will out-compete the other
  • Resource partitioning - The storing of resources so that different species can co-exist in the same area
    • Temporal - using the same resources at different times
    • Spatial - using different parts/areas of the same resource
    • Ecological - using the same resource in different habitats
  • Examples
    • Herbivores grazing in the same area
    Taller animals graze on leaves at the top of tress while others graze from the middle and lower branches
    • Partitioning of light in a forest (stratification)
    Plants grow to a certain height dependant on the light requirements
    Plants which require less light grow in the shade of taller plants
  • Predation: a predator is an organism that actively hunts, kills and consumes its prey to meet its energy needs
    • First the number of prey increases
    • The number of predators only rises after the prey numbers have increased
    • Prey numbers start to decrease
    • Predator numbers start to decrease one prey numbers are low
  • Symbiotic relationships: a close,long-term biological relationship between individuals of 2 or more species
  • Parasitism
    • One species benefits while the other species in harmed
    • parasites can be either endoparasites - those that host internally- or ectoparasites - those that host externally
  • Mutualism
    Two-different species in which both species benefit
    • Buffalo and oxpeckers
    • Sunbirds and Erica’s
  • Commensalism
    One species benefits while the other neither benefits or is negatively affected
    • Whales and barnacles
    • Short and remora fish