Competition:
- Interspecific competition is a potent force in organic evolution.
- Competition generally occurs when closely related species compete for the same resources that are limiting, but this not entirely true:
- Firstly: totally unrelated species could also compete for the same resources.
- American lakes visiting flamingoes and resident fishes have their common food, zooplanktons.
- Secondly: resources need not be limiting for competition to occur.
- Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, due to greater browsing ability.
- Competitive release: A species, whose distribution is restricted to a small geographical area because of the presence of a competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed.
- Connell’s elegant field experiment showed that superior barnacle Balanus dominates the intertidal area and excludes the smaller barnacle Chathamalus from that zone.
- Gause’s ‘competitive Exclusion Principle’: two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior will be eliminated eventually.
- Resource partitioning: If two species compete for the same resource, they could avoid competition by choosing, for instance, different times for feeding or different foraging pattern.
- MacArthur showed five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioral differences in their foraging activities.
Parasitism:
- Parasitic mode of life ensures free lodging and meals.
- Some parasites are host-specific (one parasite has a single host) in such a way that both host and parasite tend to co-evolve.
Parasitic adaptation
- Loss of unnecessary sense organs.
- Presence of adhesive organs or suckers to cling on to the host.
- Loss of digestive system.
- High reproductive capacity
- Parasites having one or more intermediate host or vectors to facilitate parasitisation of its primary host.
- Liver fluke has two intermediate hosts (snail and a fish) to complete its live cycle.
Effects on the host:
- Parasite always harms the host.
- They reduce the survival, growth and reproduction of the host.
- Reduce its population density.
- They make the host more vulnerable to the predators, by making it physically weak.
- Ectoparasite: feeds on the external surface of the host.
- Lice on human
- Ticks on dog
- Marine fish infested with copepods
- Cuscutaa parasitic plant grow on hedge plants.
- Endoparasites: are those that live inside the host body at different sites.
- Life cycle is more complex.
- Morphological and anatomical features are greatly simplified.
- Highly developed reproductive system.
- Brood parasitism:
- Special type of parasitism found in birds.
- The parasitic birds lay its eggs in the nest of its host and let the host incubate them.
- The egg of the host is very similar with the egg of the host.
- Cuckoo lays eggs in the nest of the crow.
Commensalism: This is the interaction in which one species benefits and the other is neither benefited nor harmed.
- Orchids growing as an epiphyte on a mango branch.
- Clown fish living among tentacles of sea anemone.
- Barnacles on back of whales.
- Cattle Egret and grazing cattle.
Mutualism: interaction between two living organism, both are equally benefited, no one is harmed.
- Lichen: a mycobiont and a Phycobiont.
- Mycorrhiza: relationship between fungi and root of higher plant.
- Pollinating insects and flowering plants.
- Fig trees and its pollinating agent wasp.
Sexual deceit
- Mediterranean orchid Ophrys employs ‘sexual deceit’.
- Petal of the flower resembles the female bee.
- The male bee attracted to what it perceives as a female, ‘pseudocopulates’ with the flower but does not get any benefits.
CBSE Biology (Chapter Wise) Class XII ( By Mr. Hare Krushna Giri )
Email Id : harekrushnagiri@yahoo.com
