Biotic Community Concept 1y286i

Biotic Community Concept A biotic community is any assemblage of populations living in a prescribed area or physical habitat; it is an organized unit to the extent that it has characteristics additional to its individual and population components and functions as a unit through coupled metabolic transformations. Major community are these which are of sufficient size and completeness of organization that they are relatively independent; that is, they need only for receive solar energy from the outside and are relatively independent of inputs and outputs from adjacent communities. Minor communities are those which are more or less dependent on neighboring aggregations. It is important in ecological theory because it emphasizes the fact that diverse organisms usually live together in an orderly manner. The Community 1. Autecology Also called Species Ecology, the study of the interactions of an individual organism or a single species with the living and nonliving factors of its environment. Autecology is primarily experimental and deals with easily measured variables such as light, humidity, and available nutrients in an effort to understand the needs, life history, and behaviour of the organism or species. a. Habitat and Niches A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant, or other type of organism. It is the natural environment in which an organism lives, or the physical environment that surrounds (influences and is utilized by) a species population. A habitat is made up of physical factors such as soil, moisture, range of temperature, and availability of light as well as biotic factors such as the availability of food and the presence of predators. A habitat is not necessarily a geographic area for a parasitic organism it is the body of its host or even a cell within the host's body. A niche is a term describing the relational position of a species or population in an ecosystem. More formally, the niche includes how a population responds to the abundance of its resources and enemies (e.g., by growing when resources are abundant, and predators, parasites and pathogens are scarce) and how it affects those same factors (e.g., by reducing the abundance of resources through consumption and contributing to the population growth of enemies by falling prey to them). The abiotic or physical environment is also part of the niche because it influences how populations affect, and are affected by, resources and enemies. The description of a niche may include descriptions of the organism's life history, habitat, and place in the food chain. According to the competitive exclusion principle, no two species can occupy the same niche in the same environment for a long time. b. Character displacement It refers to the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur but are minimized or lost where the species’ distributions do not overlap. This pattern results from evolutionary change driven by competition among species for a limited resource (e.g. food). The rationale for character displacement stems from the competitive exclusion principle, also called Gause's Law, which contends that to coexist in a stable environment two competing species must differ in their respective ecological niche; without differentiation, one species will eliminate or exclude the other through competition. c. Intracommunity d. Biological clocks

An internal mechanism in organisms that controls the periodicity of various functions or activities, such as metabolic changes, sleep cycles, or photosynthesis. It is also refers progression or time period from puberty to menopause, marking a woman's ability to bear children. An internal system that controls an organism's circadian rhythms, the cycles of behavior that occur regularly in a day. In mammals, the biological clock is located near the point in the brain where the two optic nerves cross. In many birds, the biological clock is located in the pineal gland. In protists and fungi, the individual cells themselves regulate circadian rhythms.

e. Ecological equivalents are species that occupy similar niches in different geographical regions. f. Behavior and Specification Behavior is the range of actions and mannerisms made by organisms, systems, or artificial entities in conjunction with their environment, which includes the other systems or organisms around as well as the physical environment. It is the response of the system or organism to

various stimuli or inputs, whether internal or external, conscious or subconscious, overt or covert, and voluntary or involuntary. Speciation refers to the evolutionary process by which new biological species arise. There are three main ideas concerning the emergence of new species (Modes of Speciation), each based on the degree to which populations undergoing this process are geographically isolated from one another (allopatric speciation, sympatric speciation, parapatric speciation).  During allopatric speciation, a population splits into two geographically isolated populations (for example, by habitat fragmentation due to geographical change such as mountain building). The isolated populations then undergo genotypic and/or phenotypic divergence as: (a) they become subjected to dissimilar selective pressures; (b) they independently undergo genetic drift; (c) different mutations arise in the two populations. When the populations come back into , they have evolved such that they are reproductively isolated and are no longer capable of exchanging genes.  Sympatric speciation refers to the formation of two or more descendant species from a single ancestral species all occupying the same geographic location.  In parapatric speciation, there is only partial separation of the zones of two diverging populations afforded by geography; individuals of each species may come in or cross habitats from time to time, but reduced fitness of the heterozygote leads to selection for behaviours or mechanisms that prevent their inter-breeding. Parapatric speciation is modelled on continuous variation within a "single", connected habitat acting as a source of natural selection rather than the effects of isolation of habitats produced in peripatric and allopatric speciation. 2. Synecology: Population Ecology The study of relationships between communities and environment. Synecology means study of structure, nature, organization and development of plant communities. a. Structure and Dynamics of Single Species Population 1. Population size-(usually denoted N) is the number of individual organisms in a population. 2. Population estimates - an official, usually periodic enumeration of a population, often including the collection of related demographic information. 3. Spatial distribution is the arrangement of a phenomenon across the Earth's surface and a graphical display of such an arrangement is an important tool in geographical and environmental statistics. A graphical display of a spatial distribution may summarize raw data directly or may reflect the outcome of more sophisticated data analysis. Many different aspects of a phenomenon can be shown in a single graphical display by using a suitable choice of different colors to represent differences. 4. Sex ratio and age distribution Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms. Age distribution, also called Age Composition, in population studies, the proportionate numbers of persons in successive age categories in a given population. Age distributions differ among countries mainly because of differences in the levels and trends of fertility. A population with persistently high fertility, for instance, has a large proportion of children and a small proportion of aged persons.  Percentage of the total population, or the population of each sex, at each age level 3. Synecology: Population Ecology a. Community Structure b. Patterns of community c. Alterations of community pattern line 4. Other pertinent Laws