Atoms combine to form molecules

Atoms combine to form molecules

 The characteristics of molecules and their organization in a cell up to speciation are discussed in the biology section. This chapter includes interaction at population and the levels above it.

Population Ecology

Population is a group of organisms of the same species that live in the same area at the same time. Certain principles govern the growth and sustainability of populations over time. Ecological interactions start within and between populations.

     Each population has its own gene pool and range of traits. It also has a characteristic size, density, and distribution pattern and age structure. Environmental conditions and species interaction influence these characteristics. Population size is generally an out -come of births, deaths, immigration and emigration. As long as the per capita birth rate remains even slightly above per capita death rate, a population can grow exponentially. Resources is short supply put limits on the growth of population. The maximum number of individuals of a population that can be sustained indefinitely be the resources in a given environment is referred as carrying capacity.

The number may rise or fall with changes in resource availability. The size of a low –density population may increase  gradually; go through a rapid growth phase, then levels off once the carrying capcity for the population  is reached. Th limiting  factors vary in their relative effects and vary over time, so, population size also changes over time. Limiting factor such as competition  for resources, disease and predation are density –dependent. Density – independent factors, such as weather on the rampage, tend to increase the death rate or decrease the birth rate more or less indepently of population density.

Community Ecology

 Community is a natural association that consisits of all populations of different species that live and interact within an area at the same time. These interactions in turn influence the structure of communities. The many ways in which organisms interact with one another are as following:

Symbiosis    Any intimate relationship or association between members of two or more species. Symbiosis is the result of co-evoluton. Flowering plants and their pollinators have a symbiotic relationship.

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