Ecosystems and Living Organisms

A genetic change in a population of organisms that happens over time.
An evolutionary modification that improves the chances of survival and reproductive success of the population in a given environment.
Natural Selection
Better-adapted individuals are more likely to survive and reproduce, increasing their proportion in the population.z
A process of community development that involves a changing sequence of species.
Pioneer Community
The first organisms to colonize (or recolonize) in an area.
Primary Succession
Ecological succession in an environment that has not previously been inhabited; initially no soil is present.
Secondary Succession
Ecological succession in a previously inhabited environment that was exposed to some kind of disturbance; soil is already present.
Any intimate relationship or association between members of two or more species.
The interdependent evolution of two interacting species; symbiosis is a result of this.
Keystone Species
Species that are vital in determining the nature and structure of the entire ecosystem; species composition and ecosystem functioning.
A symbolic relationship in which both partners benefit.
A symbolic relationship in which one partner benefits and the other partner is unaffected.
A symbolic relationship in which one partner-the parasite- obtains nutrients at the expense of the other- the host.


When a parasite causes disease and sometimes the death of the host.



The consumption of one species, the prey, by another, the predator.

Intraspecific Competition


Competition among members of the same species.

Interspecific Competiton


Competition between members of different species.

Ecological Niche
Every organism’s own role within the structure and function of an ecosystem.


The local environment in which and organism lives.

Limiting Factor
An environmental resource that, because it is scarce or unfavorable, restricts the ecological niche of an organism.
Resource Partitioning


Coexisting species’ niches differ from each other in one or more ways.

Competitive Exclusion
The concept in which with identical living requirements can occupy the same ecological niche indefinetly.