![]() ![]() Notice that survival and reproduction are “optimized,” not maximized. Life History Theory explains how evolution optimizes these survival and reproductive characteristics in different populations, affecting parameters such as: how big and fast individuals grow, when they reach sexual maturity, how many offspring they have each time they reproduce, how many times the reproduce, and when they die. How energy is allocated to these different aspects of the organisms survival is called their life history, and that energy allocation generates characteristic life history traits, traits that impact survival and reproductive output: size at birth, age at maturity, size at maturity, number and size of offspring (fecundity), reproductive value, lifespan and senescence, which we will define as the decline in fecundity with age. Individuals in a population experience a life cycle of birth, growth and development, maturity to adulthood, and then decline into reproductive senescence. Consequently, understanding how the patches and their constituent populations are arranged within the metapopulation, and the ease with which individuals are able to move among them is key to describing the population diversity and conserving the species. The extent of genetic exchange between source and sink populations depends, therefore, on the size of the populations, the carrying capacity of the habitats where the populations are found, and the ability of individuals to move between habitats. A population that requires net immigration in order to sustain itself acts as a sink. In contrast, a small population is unlikely to have a high degree of emigration instead, it can receive a high degree of immigration. For example, a large or overcrowded population patch is unlikely to be able to support much immigration from neighboring populations it can, however, act as a source of dispersing individuals that will move away to join other populations or create new ones. There may be quite different levels of dispersal between the constituent populations of a metapopulation. This group of different but interlinked populations, with each different population located in its own, discrete patch of habitat, is called a metapopulation. Individual organisms may periodically disperse from one population to another, facilitating genetic exchange between the populations. This is the case, for example, for species that live in wetlands, alpine zones on mountaintops, particular soil types or forest types, springs, and many other comparable situations. Metapopulations are populations of the same species linked together by migration ( excerpted from OpenStax CNX)Ī species that is ecologically linked to a specialized, patchy habitat may likely assume the patchy distribution of the habitat itself, with several different populations distributed at different distances from each other. Identify maximal reproductive value and explain why it changes through an organism’s lifetime.Predict whether a population is growing, shrinking, or stable with different population growth measures (r and R0).Calculate population (net) reproductive rate from life tables to determine if a population is growing or shrinking.Identify key features of an organism’s life history and how they respond to environment/natural selection regimes.Define metapopulation, reproductive value, and life history traits.Only catastrophic events tilt the balance. These extended times allow for careful tailoring of the populations. Space, food, resources: you name it they all contribute to keeping the populations down to manageable numbers, and with a reason: the characteristic times of population growth are centuries, if not more, generally outliving the lifespan of a single individual. The real world is a world of limitations. A temporary increase would necessarily result in a decrease that would bring the number back toward the carrying capacity: we say that the population is controlled by a limiting factor. The population plateaus because the environment can't support more than that number. When a population reaches the carrying capacity, the net growth rate is 0 0 0: the number of births equals the number of deaths (and the other factors affecting the number of individuals balance each other). ![]() The carrying capacity definition is the maximum size of a population sustainable by a specific environment. ![]()
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