Populations

Ecology = science of interactions between organisms and their environment

  • One of the themes is the notion that organisms are interdependent on each other in complex ways

  • includes the largest levels of biology…

    • populations, community, ecosystems


Population = all the members of one species in one area

  • this makes a population a breeding unit, potential interbreeders

  • everyone in a population is a part of the same gene pool (they evolve together as a unit)


Each population has 3 variables that you can measure:

  1. dispersion = space in between individuals

  2. distribution = where the population is found globally

  3. abundance = number of individuals


Dispersion:

  1. Clumped: for safety, mating, attraction to a common resource

  2. Uniform: territoriality (ex: sea birds guard their own nest areas by pecking at their neighbors)

  3. Random: not attracted to each other or place, but not repelled either, they just end up wherever


Distribution:

  • What limits distribution of a population?

    1. non living factors in that place (temperature, sunlight, minerals in soil, rainfall)

    2. living factors in that place (predators, parasites, competitors, pollinators)

    3. physical barriers that prevent movement


Abundance:

  • studies by demographers

r= intrinsic rate of increase (birth rate (b) - mortality rate (m) )

  • rate of increase depends on species

  • r can be positive, negative or 0

Exponential growth → ΔN/Δt = rN

  • if r = 0, it would be a horizontal line (abundance is steady)

  • if r = (-), it would be declining (heads towards extinction)

  • if r = (+), it is normal exponential

ΔN = change in abundance

Δt = change in time

Exponential graph is for unlimited growth in an ideal environment (so only measures potential growth rate)


Logistic growth: more realistic, takes into account crowding effect

  • crowding = intraspecific competition between conspecifics (members of same species)

  • better for showing competition


Competition causes density dependent mortality

  • any source of death that kills a higher percent of the population as the abundance goes up

    • ex: starvation, disease

Theoretical equilibrium that the population approaches is the carrying capacity (K) maximum abundance sustainable by a particular environment


ΔN/Δt = rN(k-n/k)