Population Ecology: Dispersion, Demography, and Growth
Population Ecology: Key Concepts
- Dispersal is the movement of individuals or gametes away from centers of high population density or from their area of origin.
- Endemic species are those that are only found in a small, specific area.
- Species transplants include organisms that are intentionally or accidentally relocated from their original distribution.
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If a transplant is successful, it indicates that the potential range of a species is larger than its actual range.
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Guppy populations evolve rapidly when predators are removed.
- Color pattern changes
- Smaller number of offspring
- Large sized offspring
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Guppy populations evolve rapidly when predators are removed.
- Population ecology explores how biotic and abiotic factors influence the abundance, dispersion, and age structure of populations.
- The most common pattern of dispersion is clumped, in which individuals aggregate in patches.
- Clumped dispersions are influenced by resource availability.
- A uniform dispersion is one in which individuals are evenly distributed.
- It may be influenced by social interactions such as territoriality, the defense of a bounded space against other individuals.
- In a random dispersion, the position of each individual is independent of other individuals.
- It occurs in the absence of strong attractions or repulsions among individuals.
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Demography is the study of these vital statistics of a population and how they change over time.
- Birth rates, Death rates, Survivorship, Reproductive rate
- A survivorship curve is a graphic way of representing the data in a life table.
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Survivorship curves can be classified into three general types:
- Type I: Low death rates during early and middle life and an increase in death rates among older age groups.
- Type II: A constant death rate over the organism’s life span.
- Type III: High death rates for the young and a lower death rate for survivors.
- dN/dt is the growth rate.
- N is population size.
- T is time.
where r is the intrinsic rate of increase, the per capita rate at which an exponentially growing population increases in size at each instant in time
- A more realistic population model limits growth by incorporating carrying capacity.
- Carrying capacity (K) is the maximum population size the environment can support.
- Carrying capacity varies with the abundance of limiting resources.
- In the logistic population growth model, the per capita rate of population growth approaches zero as the population size nears carrying capacity (K).
- When N is small compared to K, the term (K – N)/K is close to 1, and the per capita rate of population growth will be close to r.
- When N is large compared to K, the term (K – N)/K is close to 0, and the per capita rate of population growth is small.
- When N equals K, the population stops growing.
- The population growth rate decreases as N approaches K.
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Reproductive strategy is an important aspect of a species’ life history.
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Species that exhibit semelparity, or big-bang reproduction, reproduce once and die.
- Insects
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Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly.
- Mammals
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Species that exhibit semelparity, or big-bang reproduction, reproduce once and die.
- K-selection is selection for life history traits that are advantageous at high population densities.