Graph your results. Density-dependent growth : In a population that is already established, resources begin to become scarce, and competition starts to play a role.
We refer to the maximum number of individuals that a habitat can sustain as the carrying capacity of that population. If a population overshoots its carrying capacity by too much, nobody gets enough resources and the population can crash to zero. If the population approaches its carrying capacity more gradually, these limiting factors, such as food, nesting sites, mates, etc.
The "logistic equation" models this kind of population growth. Compare the exponential and logistic growth equations.
Take the equation above and again run through 10 generations. Start with an initial population size N i of Although each species has specific tolerances for environmental toxins, amphibians in general are particularly susceptible to pollutants in the environment. For example, pesticides and other endocrine disrupting toxins can strongly control the growth of amphibians Blaustein et al.
These chemicals are used to control agricultural pests but also run into freshwater streams and ponds where amphibians live and breed. They affect the amphibians both with direct increases in mortality and indirect limitation in growth, development, and reduction in fecundity. Rohr et al. These effects limit population growth irrespective of the size of the amphibian population and are not limited to pesticides but also include pH and thermal pollution, herbicides, fungicides, heavy metal contaminations, etc.
Environmental catastrophes such as fires, earthquakes, volcanoes and floods can strongly affect population growth rates via direct mortality and habitat destruction. A large-scale natural catastrophe occurred in when hurricane Katrina impacted the coastal regions of the Gulf of Mexico in the southern United States. Katrina altered habitat for coastal vegetation by depositing more than 5 cm of sediment over the entire coastal wetland zone. In these areas, substantial improvement in the quality of wetlands for plant growth occurred after many years of wetland loss due to control of the Mississippi River flow Turner et al.
At the same time, however, almost km 2 of wetland was destroyed and converted to open sea, completely eliminating wetland vegetation Day et al. More recently the Gulf oil spill in has again impacted the coastal wetland vegetation. Though human derived, this large-scale environmental disaster will have long-term impacts on the population growth of not only vegetation but all organisms in the wetlands and nearshore regions of the Gulf of Mexico.
Blaustein, A. Ultraviolet radiation, toxic chemicals and amphibian population declines. Diversity and Distributions 9, — Clutton-Brock, T.
Sex differences in emigration and mortality affect optimal management of deer populations. Nature , — Conroy, J. Recent increases in Lake Erie plankton biomass: roles of external phosphorus loading and dreissenid mussels. Journal of Great Lakes Research 31 Supplement 2 , 89— Day, J. Restoration of the Mississippi delta: lessons from hurricanes Katrina and Rita.
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Introduction to Population Demographics. Population Dynamics of Mutualism. Population Ecology Introduction. Population Limiting Factors. The Breeder's Equation. Global Atmospheric Change and Animal Populations. Semelparity and Iteroparity. Causes and Consequences of Dispersal in Plants and Animals. This hypothesis was tested and disproved in a study which showed that female weight had no influence.
The actual cause of the density-dependence of fecundity in this organism is still unclear and awaiting further investigation. Many factors, typically physical or chemical in nature abiotic , influence the mortality of a population regardless of its density. They include weather, natural disasters, and pollution. An individual deer may be killed in a forest fire regardless of how many deer happen to be in that area.
Its chances of survival are the same whether the population density is high or low. In real-life situations, population regulation is very complicated and density-dependent and independent factors can interact.
A dense population that is reduced in a density-independent manner by some environmental factor s will be able to recover differently than would a sparse population. For example, a population of deer affected by a harsh winter will recover faster if there are more deer remaining to reproduce.
Learning Objectives Differentiate between density-dependent and density-independent population regulation.
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