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Transcript
Understanding Populations Environmental Science Holt Chapter 8 How Populations Change in Size Chapter 8.1 What is a population? Population: all the members of a species living in the same place at the same time Refers to both the group in general and to the size of the group Properties of Populations Populations may be described in terms of size, density or dispersion. Population density is the number of individuals per unit area or volume A population’s dispersion is the relative distribution or arrangement of its individuals within a given amount of space May be even, clumped or random How does a population grow? A population gains individuals with each new offspring or birth and loses them with each death Growth rate: a change in the size of a population over a given period of time Change in population size = Births – Deaths Can the growth rate be negative? How fast can a population grow? A species’ biotic potential is the fastest rate at which its populations can grow. Is limited by it’s reproductive potential Reproductive potential: the maximum number of offspring that each member of the population can produce How fast can a population grow? Populations may undergo exponential growth which means they’ll grow faster and faster Will only occur in nature when populations have plenty of food and space, and little to no competition or predators What limits population growth? The carrying capacity of an ecosystem for a particular species is the maximum population that the ecosystem can support indefinitely What limits population growth? A species reaches its carrying capacity when it consumes a particular natural resource at the same rate at which the ecosystem produces the resource That resource is called a limiting resource Two Types of Populations Regulation Population size can be limited that may or may not be dependent on the population density Density dependent: deaths occur more quickly in a crowded population; limited resources, predation and disease Density independent: portion of the population dies regardless of the population’s density; severe weather, natural disasters How Species Interact with Each Other Section 2 Ways in which species interact Symbiosis A relationship in which two species live in close association, typically one species will benefit from the relationship An Organism’s Niche Niche: A species’ physical home The environmental factors necessary for the species’ survival All of the species’ interactions with other organisms Habitat: is a location only. Ways in which species interact 4. Mutualism A close relationship between two species in which each species provides a benefit to the other Ways in which species interact Competition: a relation in which different individuals or populations attempt to use the same limited resource 1. • • Intraspecies competition – among members of the same species (occupy the same niche) Interspecies competition – among members of different species (niches overlap) Ways in which species interact 2. Predation: An organism that feeds on another organism is called a predator The organism that it feeds on is called prey Ways in which species interact 3. Parasitism: An organism that lives in or on another organism and feeds on it is a parasite Ways in which species interact 5. Commensalism A relationship in which one species benefits and the other species is neither harmed nor helped is called commensalism