Natalie Marchetti ISCI 2001 Spring 2015 Chapter Summaries Chapter 21: Ecology and the Environment What is Ecology? • Ecology is defined as the interactions between living organisms and their environment. The environment includes biotic (living) and abiotic (nonliving) factors. • Ecology is studied as a hierarchy of biological systems in interaction with their environments. Hierarchy of Biological Systems Organism à population à community à ecosystem à biosphere A population is a group of interbreeding organisms of the same species occupying a given area (habitat) at a given time. A habitat is the physical space where an animal lives, its environment. A community consists of all the populations of all species occupying a given area (habitat) at a given time An ecosystem is the combination of the community and its environmental factors (temperature, water, pH, light, etc.) The biosphere is the largest ecosystem or can be thought of as all the ecosystem of the planet earth (land, water & atmosphere of the planet) An organism’s role in the environment • niche - the role (or job) of an organism in an ecological community; its unique way of life and its relationship to other biotic and abiotic factors • fundamental niche - all the environmental conditions an animal can potentially tolerate • realized niche - the subset of potential suitable environments that an animal actually experiences • Organisms exist in nature as members of populations • A group of organisms of the same species may be comprised of one cohesive population or it may be composed of several geographically disjunct populations ( demes ) which still may interbreed (same gene pool) • Migration of some individuals within the demes imparts some evolutionary cohesion and reduces the chance of speciation. • Each population or deme has a 3 main characteristics: age structure sex ratio growth rate . • Resource abundance explains why populations differ in these traits. • The study of these properties and the factors that influence them is referred to as demography . • One of the key demographic measurements of populations is the survivorship curve.
• The curve measures the percent of a cohort (generation) of a given population that will die as time increases. There are 3 main types: Type 1 (e.g. humans) Type 2 (e.g. birds with parental care) Type 3 (e.g. most egg laying invertebrates and fish) • Populations of organisms containing multiple cohorts generations exhibit age structure . • Analysis of the age structure of a population can reveal whether a population is actively growing, stable, or declining. Population Growth and Intrinsic Regulations and Extrinsic Limits • Darwin recognized that all populations have the inherent ability to grow exponentially.
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