ECOLOGY

by Purwaning Rohmah/BIO off A 2015 UM

CHARACTERISTIC OF COMMUNITY

Ecologists have given variety of meanings to the term community (Schoener, 1986; Fauth et al., 1996). The term has been used by many of them for associations of plants and animals occurring in a particular locality and dominated by one or more prominent species or by some physical characteristic (Daubermiire, 1968).

A community, technically often referred to as biota or biotic community is a local association of several species populations. According to Krebs (1994), a community is an assemblage of the populations of living organisms in a prescribed area or habitat. According to Clarke (1954), a group of mutually adjusted plants and animals inhabiting a natural area is known as a community. He prefers to use the term biocenose (a shortened form of the word “biocoenosis” coined by Mobius in 1880) for community. When territorial ranges of several species populations overlap, they may coexist within a given limited area.

The organisms in such an area represent a community (Fig. 4.1). A community always contains plants as well as animals, because both are very necessary for the survival of the community. Just as populations possess characteristics above and beyond those of their component organisms, the community also exhibits characteristics above and beyond those of its constituent populations.

A major community is the smallest ecological unit that is self-sustaining and self-regulating. It is made up of a large number of smaller minor communities that are not altogether self-sustaining. For example, forests and ponds are major communities; decaying logs and ant hills are minor communities. Members of a major community are relatively independent of other communities, provided they receive radiant energy from the sun. These members normally show a similarity in their physiological make-up, behaviour, and mode of life.

The characteristic of community are:

1. SPECIES DIVERSITY

In an ecosystem ecology  each community is composed of taxonomically different species. Species diversity refers to number of different species in community both abundant and rare species. Species diversity has two components.

·         Species richness: it refers different types of species and their numerical strength. Technically it refers to ratio between different species (s) and total number of species (n).

·         Species evenness: it refers to a measure which qualifies as to how even species are in terms of their number.

Species diversity can be measured by using various diversity indices. the mathematical  expression based on species abundance data. species diversity can be measured separately either  as species richness or  evenness or diversity as a whole.

2. RESILIENCE AND RESISTANCE

For a community to be stable, it requires two components-resilience and resistance.

·         Resilience: resilience is a ability of a community to recover after facing a disturbance or displacement.

·                     Resistance: it is the ability to avoid disturbance(any event that alter the structure of a community) or displacement(shifting of the community to some other place)

      3.      DOMINANCE

Usually one community has one or more species which occur in large number. such species are called dominant and the community is often named after them.

       4.      DIVERSITY

The community consists of different group of plants and animals of different species, may be large or small, may belong to one life form or another but are essentially growing in a uniform environment.

       5.      PERIODICITY

This includes study of various life processes (respiration, growth, reproduction etc.) In the various seasons of the year in the dominant species in the community. The recurrence of these important life processes at regular intervals in a year and their manifestation in nature is called periodicity.

      6.      STRATIFICATION

Natural forest communities possess a number of layers or stores related to the high of plant. for example ,tall trees, smaller trees, shrubs and herbaceous layers from different strata. this phenomenon in a plant community is called stratification.

       7.      ECOTONE AND EDGE EFFECT:

·         Ecotone: each community has spatial limits or boundaries. the boundaries between communities may be very sharp. such as, boundaries between a forest and a lake or the boundary may be less sharp ,e.g., boundary between two types of forest or a forest and a grassland community. often there is some transitional area in between two communities that is known as ecotone. Where species of both adjacent communities are found. Ecotone is
a marginal zone and easily recognizable.

·         Edge effect: usually in one ecotone the variety of one species is larger than in any of the adjacent communities. a phenomenon of increased variety and intensity of plants at the common junction is called  edge effect and essentially due to wider range of suitable environmental conditions.

      8.      ECOLOGICAL NICHE

Different species of animals and plants fulfill different functions in the ecosystem ecology. the role of each is spoken of as its ecological niche. that is the role that a species plays in its ecosystem. The total range of its interaction with other species of its environment is known as ecological niche.

We can also say that ecological niche is a small habitat  within a habitat, in which only a single species can survive. E.P. Odum  has differentiated  habitat and ecological niche  by saying that the habitat is an organism’s  address and the ecological niche is its profession.

      9.      KEYSTONE SPECIES

In an ecological community, there are some little players and some big players. the biggest players of all are referred to as keystone species. Keystone species is first coined by by Paine in 1966.

A keystone species may be defined as one whose presence or absence, decrease or increase in abundance, strongly affects  other species in the community.
Paine through his classic experiments showed that predators and herbivores can manipulate relationships among species at lower trophic level s and thereby, control the structure of  the community. such predator species are called keystone species or keystone predator.

      10.  INTERSPECIFIC ASSOCIATION

Interspecific association: species interact with various way. Such as: competition, predation, parasitism, mutualisms, commensalisms etc.

·         Competition: species can compete with each other for finite resources. it is considered to be an important limiting factor of population size, biomass and species richness. Direct competition has been observed between individuals, population and species. Example-a lion chasing a hyena from a kill, or a plant releasing  allelopathic chemicals to impede the growth of a competing species.

·         Predation: predation is hunting another species for food. there is a positive negative interaction. Some predators kill their prey before eating them(e.g., a hawk killing a mouse),herbivores feed on plants(e.g., a cow grazing). Predation may effect  the population size of predators and prey and the number of species coexisting in a  community.

·         Mutualism: mutualism is an interaction between species in which both are benefited. Example-rhizobium bacteria growing in nodules on the roots of legumes and insects pollinating the flower of angiosperms.

·         Commensalism: commensalism is a type of relationship among organisms benefits while the other organism is nither benefited nor hermed.the organism that benefited is called the commensalism. While  the other organism that is neither benefited nor harmed is called host.
Example-an epiphytic orchid attached to the tree for support neither benefits the tree for support benefits the orchid but neither harms nor benefits the tree.