Data

Copy and paste the text below. It is read-only. Select All

Population The second level of complexity composed of all individuals that belong to the same species and live in a given area at a particular time. Evolution occurs at the level of the population. Levels of complexity Environmental scientists study nature at several different levels of complexity, ranging from the individual organism to the biosphere. At each level, scientists focus on different processes. Individual The simplest level where natural selection operates at the level of the individual because it is the individual that must survive and reproduce. Community The third level of complexity incorporates all of the populations of organisms within a given area. Like those of a population, the boundaries of a community may be defined by the state or federal agency responsible for managing it. Ecosystem Consists of all of the biotic and abiotic components in a particular location. Ecosystem ecologists study flows of energy and matter, such as the cycling of nutrients through the system. Biosphere The largest and most complex system environmental scientists study, which incorporates all of Earth's ecosystems. Scientists who study the biosphere are interested in the movement of air, water, and heat around the globe. Biome When terrestrial communities in different parts of the world experience similar patterns of temperature and precipitation, those communities can be grouped into biomes that contain plants with similar growth forms. Dynamic Constant change. (All populations are this) The exact size of population The difference between the number of inputs to the population (births and immigration) and outputs from the population (deaths and emigration) within a given time period. Population Ecology The study of factors that cause populations to increase or decrease. If births and immigration exceed deaths and emigration, the population will grow. If deaths and emigration exceed births and immigration, the population will decline and, over time, will eventually go extinct. Population Characteristics To understand how populations change over time, we must first examine some basic population characteristics. These characteristics are population size, density, distribution, sex ratio, and age structure. Population size the total number of individuals within a defined area at a given time. Example of Population Size The California condor once ranged throughout California and the southwestern United States. Over the past two centuries, however, a combination of poaching, poisoning, and accidents (such as flying into electric power lines) greatly reduced the population's size. By 1987, there were only 22 birds remaining in the wild. Population density the number of individuals per unit area (or volume, in the case of aquatic organisms) at a given time. Knowing a population's density, in addition to its size, can help scientists estimate whether a species is rare or abundant. Example of Population Density the density of coyotes (Canis latrans) in some parts of Texas might be only 1 per square kilometer, but in other parts of the state it might be as high as 12 per square kilometer. Scientists also study population density to determine whether a population in a particular location is so dense that it might outstrip its food supply. Why population density is useful Managers may divide the entire population of an animal species that is hunted or fished into management zones. These management zones may be human-defined areas, such as counties, or areas with natural boundaries, such as the major water bodies in a state. Wildlife managers might offer more hunting or fishing permits for high-density zones and fewer permits for low-density zones. Population distribution A description of how individuals are distributed with respect to one another. Random Distribution No pattern to the locations where individuals grow/live. Uniform Distribution Individuals are evenly spaced. Uniform distributions are common among territorial animals, such as nesting birds that defend similar sized areas around their nests. Uniform distributions are also observed among plants that produce toxic chemicals to prevent other plants of the same species from growing close to them. Clumped Distribution Common among schooling fish, flocking birds, and herding mammals, are often observed when living in large groups enhances feeding opportunities or protection from predators. Sex Ratio The ratio of males to females. In most sexually reproducing species, the sex ratio is usually close to 50:50. Sex ratios can be far from equal in some species, however. Age Structure A description of how many individuals fit into particular age categories. Knowing a population's age structure helps ecologists predict how rapidly a population can grow. Density-dependent factors Influence an individual's probability of survival and reproduction in a manner that depends on the size of the population. The amount of available food, for example, is a density-dependent factor. Limiting Resource A resource that a population cannot live without and which occurs in quantities lower than the population would require to increase in size. If a limiting resource decreases, so does the size of a population that depends on it. Carrying Capacity Population growth slowed as population size increased because there was a limit to how many individuals the food supply could sustain. Knowing the carrying capacity for a species, and what its limiting resource is, helps us predict how many individuals an environment can sustain. Denoted as K. Density-Independent Factors Have the same effect on an individual's probability of survival and amount of reproduction at any population size. A tornado, for example, can uproot and kill a large number of trees in an area. However, a given tree's probability of being killed does not depend on whether it resides in a forest with a high or low density of other trees. Growth Rate The number of offspring an individual can produce in a given time period, minus the deaths of the individual or its offspring during the same period. Intrinsic Growth Rate Under ideal conditions, with unlimited resources available, every population has a particular maximum potential for growth. Exponential Growth Model A growth model that estimates a population's future size (Nt) after a period of time (t), based on the intrinsic growth rate (r) and the number of reproducing individuals currently in the population (N0). J-Shaped Curve When populations are not limited by resources, their growth can be very rapid, as more births occur with each step in time. Logistic Growth Model Describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment (K?). S-Shaped Curve If a population starts out small, its growth can be very rapid. As the population size nears about one-half of the carrying capacity, however, the population's growth begins to slow. As the population size approaches the carrying capacity, the population stops growing. Overshoot When a population becomes larger than the environment's carrying capacity. Die-Off A rapid decline in a population due to death K-Selected Species A species with a low intrinsic growth rate that causes the population to increase slowly until it reaches carrying capacity. Typically large organisms that reach reproductive maturity relatively late, produce a few, large offspring, and provide substantial parental care. (Large mammals and most birds) R-Selected Species A species that has a high intrinsic growth rate, which often leads to population overshoots and die-of s. Do not typically remain near their carrying capacity, but instead exhibit rapid population growth that is often followed by overshoots and die-offs. Among animals, r-selected species tend to be small organisms that reach reproductive maturity relatively early, reproduce frequently, produce many small offspring, and provide little or no parental care. Survivorship Curve A graph that represents the distinct patterns of species survival as a function of age. Corridor A strip of natural habitat that connects separated populations. Metapopulation A group of spatially distinct populations that are connected by occasional movements of individuals between them. Provides species with a lesser chance of extinction and disease Community Ecology The study of interactions between species. (competition, predation, mutualism, and commensalism) Competition The struggle of individuals to obtain a limiting resource. Competitive Exclusion Principle The principle stating that two species competing for the same limiting resource cannot coexist. Under a given set of environmental conditions, when two species have the same realized niche, one species will perform better and will drive the other species to extinction. Resource Partitioning A situation in which two species divide a resource, based on differences in their behavior or morphology. Temporal Resource Partitioning When animals' hunt at different times. Morphological Resource Partitioning When species evolve in order to partition a territoy. Spacial Resource Partitioning Splitting up the territory. (Shallow and deep roots) True Predator A predator that typically kills its prey and consumes most of what it kills. Herbivore A predator that consumes plants as prey. Parasite A predator that lives on or in the organism it consumes. Pathogen An illness-causing bacterium, virus, or parasite. Parasitoid An organism that lays eggs inside other organisms. Causes death to host. Mutualism An interaction between species that increases the chances of survival or reproduction for both species. Commensalism A relationship between species in which one species benefits and the other species is neither harmed nor helped. Symbiotic A relationship of two species that live in close association with each other. Keystone Species A species that is far more important in its community than its relative abundance might suggest. Predator-Mediated Competition Competition in which a predator is instrumental in reducing the abundance of a superior competitor, allowing inferior competitors to persist. Ecosystem Engineer A keystone species that creates or maintains habitat for other species. Ecological Succession The replacement oflone group of species by another group of species over time. Primary Succession Ecological succession occurring on surfaces that are initially devoid of soil. Secondary Succession The succession of plant life that occurs in areas that have been disturbed but have not lost their soil. (Forest Fire) Pioneer Species A species that can colonize new areas rapidly. The Species Richness of a Community is Influenced by: Latitude, time, habitat size, and distance The Theory of Island Biogeography A theory that demonstrates the dual importance of habitat size and distance in determining species richness.