Chapter 6 Outline
I. Population Dynamics and Carrying Capacity
* Populations change in size, density, and age distribution; most members of populations live together in clumps or groups. * Three general patterns in a habitat: clumping, uniform distribution, and random dispersion. Most live in clumps or groups. * Availability of resources varies from place to place.
* Living in groups offers better protection from predators. * Some predator species live in packs to better have a chance to get a meal. * Temporary groups may form for mating and caring for young. * Uniform pattern distribution may occur where a resource is scarce. * Four variables influence population size: births, deaths, immigration, emigration. * Increase in population -birth and immigration.
* Decrease in population - death and emigration.
* Age structure of a pop. is usually described as the pre-reproductive stage, reproductive stage and post-reproductive stage. * large reproductive stage is likely to increase, while a population with a large post-reproductive stage is likely to decrease. * No population can grow indefinitely due to limited resources such as light, water, and nutrients and also due to competitors and/or predators. biotic potential is the populations capacity for growth.
* intrinsic rate of increase is the rate of population growth with unlimited resources. * Rapidly growing populations have four characteristics.
* reproduce early in life
* short periods between generations
* long reproductive lives
* multiple offspring each time they reproduce.
* Environmental resistance - factors that limit population growth. * Carrying capacity is determined by biotic potential and environmental resistance. This is the number of a species’ individuals that can be sustained indefinitely in a specific space. * As a population reaches its carrying capacity, its growth rate will decrease because resources become more scarce. * A population can grow rapidly with ample resources. * exponential growth - fixed rate of growth that will be a J-shaped growth curve * Exponential growth leads to logistic growth and may lead to the population overshooting the environment’s carrying capacity. * If the carrying capacity of an area is exceeded, changes in the area itself can reduce future carrying capacity. Reducing grass cover by overgrazing allows sagebrush to move in and reduces the number of cattle that the land can support.
* Technological, social, and cultural changes have extended the earth’s carrying * The density of a population may or may not affect how rapidly it can grow. * Density-independent affect a population’s size regardless of its density. * Density-dependent have a greater affect on the population as its density increases. Infectious disease * Four general types of population fluctuations in nature are: stable, irruptive, cyclic, and irregular. * stable population fluctuates slightly above and below carrying capacity * Some species have a fairly stable population size that may occasionally irrupt to a high peak and then crash to below carrying capacity
II. Interactions between predators and their prey change in cycles and appear to be caused by species interactions, but other factors may be involved. * top-down control of prey by predators may not be the only explanation for the boom-and-bust cycles seen in these populations. This may also be related to the food supply of prey. * The bottom-up control hypothesis states that plants are consumed too rapidly by prey for replacement to keep up. This may lead to a crash of plant predators, and that may lead to a crash of higher predators of the herbivores. * These are not mutually exclusive hypotheses; more...