Population Ecology
- Exponential growth and doubling time:
- Exponential growth: growth at a constant rate of increase per unit of time. The sequence follows a geometric rate of increase (ex. 2,4,8,16)
- Doubling time: Amount of time necessary for the population to double. 70 / annual % growth (ex. Populations growing at 35% will double every 2 years.)
- Population Oscillations:
- Population exceeds carrying capacity or limiting factors come into effect, death rates surpass birth rates = crash or dieback
- Extent to which a population exceeds the carrying capacity = overshoot
- Population explosion followed by a population crash = irruptive/ Malthusian growth
- Sometimes populations go through cycles of exponential growth and catastrophic crashes, usually they are quite regular if they depend on certain factors like seasonal light, temperature. May be irregular if they depend on complex environmental and biotic relationships.
- Carrying Capacity:
- Carrying Capacity: the maximum number of individuals of any species that can be supported by a particular ecosystem on a long-term basis.
- Catastrophic Population Decline:
- Catastrophic System: when the population jumps from one seemingly steady state to another without any intermediate stages.
Factors that Increase/Decrease Populations
- Natality, Fecundity and Fertility:
- Natality: production of new individuals, main source of adding to populations, sensitive to environmental conditions (nutritional levels, climate, soil and water conditions, social interaction between species),
- Fecundity: physical ability to reproduce
- Fertility: measure of the actual number of offspring produced.
- Immigration: Seeds, spores, and small animals may be introduced by wind, water (major source of organisms to islands), carried inside other animals, walking, swimming, flying,
- Mortality and Survivorship:
- Mortality: death rate, death rate is found by dividing the number of organisms that die in a certain time period by the number alive at the beginning of the period.
- Survivorship: the percentage of a certain organism that lives to be a certain age.
- Life Expectancy: probable number of years of survival of an
individual of a given age.
- Life Span: longest period of life reached by a given type of
organism.
Survivorship Curves gives us the predicted life expectancy at each age interval. Humans in the first world have a high survivorship when young and most likely live to old age. Most marine organisms have a low survivorship- they are cast out into the waters, but once they survive that trauma they are likly to live out their full age. Hyrdas and sea gulls randomly die throughout their lives.
-Age Structure Diagrams/Histograms:
- An outcome of the interaction between mortality and natality.
- Bigger towards the bottom- rapidly expanding population
- Pretty equal throughout- stable population
- Bigger at the middle/top- diminishing population
- Emigration: movement of members out of the population
Factors that Regulate Population Growth
- Density dependent and independent factors and Biotic/Abiotic:
- Mostly these things affect natality and mortality, therefore changing the population.
- Intrinsic: operating within individual organisms or between organisms of the same species.
- Extrinsic: imposed from outside the population
- Biotic: caused by living organisms
- Abiotic: caused by non-living components of the environment
- Density dependent: effects are stronger or a higher percentage of the population is affected as the population density increases (food shortage)
- Density independent: the effect is the same or a constant proportion of the population is affected regardless of the population density (fire, climate conditions, volcano)
- In general, biotic factors are density- dependent while abiotic factors are density-independent
