Ecological Knowledge and Environmental Problem-Solving Concepts and Case Studies (1986) / Chapter Skim
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1. Individuals and Single Populations
1. Individuals and Single Populations
Pages 23-37
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From page 23... ...
Studies of particular species yield the detailed information needed for management with respect to nutrient and habitat requirements, important interactions with other species, reproductive requirements, and significant behavioral idiosyncrasies. Moreover, research on organisms with complex life cycles has shown the importance of choosing the appropriate stages in the life cycle 23
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From page 24... ...
To determine how a population will respond to an increase in mortality due to harvesting or stress or how effective a given procedure might be for improving reproductive output, we need some understanding of population dynamics. Research in population dynamics has ranged from field studies designed to determine what factors affect population sizes in an area to theoretical studies of how such factors can act together to "regulate" population size over long periods.
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From page 25... ...
Changing such population characteristics as total numbers, distributions of ages and sizes, and sex ratio not only changes the dynamics of a population, but also establishes a potential for evolutionary change in traits that exhibit genetic variation. Population management that is based only on dynamic considerations can in the long run produce results opposite to those intended.
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From page 26... ...
The control of malaria was less successful than expected, because of a behavioral polymorphism in habitat selection (Chapter 151. Attempts to find suitable natural predators to control agricultural and forest pests usually involve searches in areas with climates similar to those of the areas into which the control agent is to be introduced (Chapter 14~.
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From page 27... ...
In more complex animal systems, reproductively mature adults gather, choose mates from the available pool, and associate with one another for various periods after fertilization to care for each other or their offspring. In many species, mate selection is combined with habitat selection for breeding, especially in species in which one adult holds space that contains resources for the reproductive cycle.
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From page 28... ...
The vampire bat case study is an excellent example of the value of detailed natural-history observation for population management. POPULATION DYNAMICS Population Regulation Environmental changes can influence a population in two basic ways, each having important management implications.
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From page 29... ...
Because yield is a result of both the reproductive rate and the number of individuals reproducing, yield is highest when the population is between low density (few individuals but high individual reproductive rate) and the high density of natural equilibrium (strong density-dependent reduction of average individual reproductive output or survival)
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From page 30... ...
has modeled minimal population sizes and areas for grizzly bears in Yellowstone National Park by using successive computer simulations based on estimated population parameters with random variation. Using several scenarios, he estimated that 35-70 bears were needed to have a 95% probability of population survival for 100 years in that ecosystem.
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From page 31... ...
For example, winter resources might limit the number of individuals that survive to breed, so an increase in the preceding summer reproduction could cause little change in the number of individuals breeding in the following summer. This idea is particularly important in managing bird species that winter in tropical habitats undergoing extensive deforestation.
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From page 32... ...
Isolated populations have less potential for recovering from temporary reductions when immigration rates are low, as happens when an occupied habitat becomes an island surrounded by unsuitable habitat. Maintaining travel corridors of appropriate habitat to connect populations, particularly of species at low density and with strict habitat requirements and poor dispersal ability, might be a key component of management (MacClintock et al., 1977; Willis, 19741.
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From page 33... ...
Expected reproductive output is smaller in late reproductive stages than in early stages, so late stages have a smaller per capita effect on population production. Similarly, many individuals in prereproductive stages will not survive to breed, so their removal affects population reproduction less than the removal of early breeders.
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From page 34... ...
Sex Ratios and Sex Biases Either intentionally or unintentionally, human activities often produce mortality differences between the sexes and thus biased sex ratios. The effects on population reproduction and dynamics depend on the form of the mating system.
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From page 35... ...
In retrospect, it should have been obvious that it would happen; in fact, the use of poisons to produce a class of resistant organisms for experimental purposes has been a major technique of microbiology for more than 50 years. The short generation times, high reproductive rates, and large populations of most pests favor rapid evolution (May and Dobson, 19851.
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From page 36... ...
The theory suggests ways of reducing the proportion of jacks despite heavy harvesting of larger males. For example, spawning sites could be manipulated to reduce the cover in which the jacks seek protection from larger males, thus lowering their reproductive success and the proportion of jacks in the next generation.
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From page 37... ...
(Ne is the number of potential breeding individuals in an "ideal" population one with random mating, a sex ratio of 1: 1, discrete generations, constant size, and a Poisson distribution of family size that retains the same amount of selectively neutral genetic variability as the population under consideration. If the population departs from "ideal" conditions, as occurs commonly in nature, Ne is lower than actual N.)
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