Biotic Factors :
The vital activities (such as growth, nutrition, reproduction, pollination etc) of the organisms and the effect of their interactions are termed as biotic factors. Odum (1971) divided the biotic relations into two groups viz.-
Positive Interactions :
In these interactions one or more species are benefited. Such as mutualism, protocooperation, commensalism.
(1) Symbiosis :
A permanent relationship between two different species (dissimilar organism) in which both are benefited. It may also be called as obligatory mutualism.
Examples : Lichens. Rhizobium, Mycorrhiza etc. Mycorrhizal assocation occurs between the roots of higher plants & fungus.
Examples : Pinus. Oak. Hickories. Birch etc. The fungus absorbs the water & minerals to provide to the plants and in tum obtain other nutrients from the roots. Absorption of phosphorus from the soil is perform by the fungus. Such roots are without root hairs.
(2) Protocooperation :
It is a temporary relationship between two different species (dissimilar organisms) in which both are benefited. It is also called as non- obligatory mutualism.
Examples : Sea anemone & Hermit crab. The hermit craps lives in an empty gastropod shell to which sea anemone/s remain attached. They may live independently also.
(3) Commensalism :
The relationship between two different species (dissimilar organisms) in which one is benefited & second remains unaffected (Neither loss nor benefit).
Examples : (i) Epiphytes & Epizoans – The epiphytes are autotrophs which grow on other plants for support. They have hanging roots bearing velamen which absorb atmosheric humidity. They synthesize their own food by photosynthesis. Such as Vanda & Orchids. Green algae Basicladia grow on the shell (back) of fresh water turtles. It can be an examples of epizoan.
Example : (ii) Lianas – They are long – stemmed woody vines, that are rooted in the soil at ground level and use trees to climb up to the canopy to get access to well-lit areas of the forest. Examples – Tinospora, Bignoia, Bouganvilliaetc.
Negative Interactions :
The relationship between two dissimilar organisms in which one or both remain in loss. It is also called as antagonism. They are of three types –
1. Exploitation,
2. Antibiosis &
3. Competition
1. Exploitation :
In this relationship one species directly or indirectly hanns other species to get support, shelter or food and mainly for food. The exploitation for food is of two types :
- Parasitism: A relationship between two dissimilar organisms in which one is benefited (Parasite) and second remains in loss (host)
Examples : Leach, Dodder (Amarbel), Striga, Purple toothwort, Cuscuta, Aureolaria (Orobanchaceae)
- Predation : Some animals feed on other organisms which may be herbivorers or carnivores and are called as predators. The plant eater predators are called as herbivores such as some fungi (Dactyella, Zoophagus), Insects, Nematods etc. Some plants feed on insects and are called as insectivorous plants. Such as Drosera, Nephenthes, Utricularia, Dionea etc. They have various organs to feed insects.
2. Antibiosis :
In this relationship, one organism secretes some chemicals which partially or completely inhibit the growth of other organism and lead to death. The roots of some higher plants secrete toxic chemicals which inhibit the germination of seeds of plants of other species. It is called as allelopathy. Examples – Allelopathy parthenium, Lantana, Eucleptus etc. Antibiosis is applicable on microorganisms such as fungi, bacteria, actinomycetes etc.
3. Competition :
Similar environmental needs develop competition among organisms. This competition is mainly for shelter, food, light, water etc. The competition among the organisms of same species is called as intraspecific competition and among the organisms of different species is termed as interspecific competition.
