Biology 2 Marks Questions

→ (a) Commensalism : This is the interaction in which one species benefits and the other is neither harmed nor benefited.
Examples :
→ An orchid growing as an epiphyte on a mango branch
→ barnacles growing on the back of a whale
→ (b) Parasitism : Parasitism is an interaction in which one species (smaller one) get benefit and another species (bigger one) get harmed.
Examples :
→ Ectoparasite: lice on humans and ticks on dogs.
→ Many marine fish are infested with ectoparasitic copepods.
→ Endoparasite : liverfluck, tape worm, ascaris etc.
→ (c) Camouflage : Prey species have evolved various defenses to lessen the impact of predation.
Some organisms are cryptically-coloured (camouflaged) to avoid being detected easily by the predator.
→ Some species of insects and frogs
→ (d) Mutualism : This interaction confers benefits on both the interacting species.
Examples :
→ Lichens, mycorrhiza, fig tree and some species of wasps.
→ (e) Interspecific competition : It is an interaction between two species in which both are in loss.
→ Example: some shallow South American lakes, visiting flamingoes and resident fishes compete for their common food, the zooplankton in the lake.

(a) Population :
→ Population has different attributes.
→ Our human population also has variety like rural population, urban population, altitude population or the population of a country.
→ In genetics population means, the group of organisms belong to same species and can reproduce with each other.
→ Normally, one species can not reproduce with another species. For this many physical and biological barriers are there.
→ Population can be limited to small region or expanded to large region. Example: population of sludge or population of Island.
(b) Community :
→ Different group of species which exists in a specific geographical area for specific time is called Community.

→ Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population.
→ Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species.

→ It is an example of Commensalism. (+, O)
→ This is the interaction in which one species benefits and the other is neither harmed nor benefited.
→ An orchid growing as an epiphyte on a mango branch but mango doesn't get any nourishment.
→ In this interaction orchid gets abiotic factors easily.

→ Plants have evolved an astonishing variety of morphological and chemical defences against herbivores.
→ Thorns (Acacia, Cactus) are the most common morphological means of defence.
→ Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it.
→ The weed Calotropis growing in abandoned fields.
→ The plant produces highly poisonous cardiac glycosides and that is why you never see any cattle or goats browsing on this plant.
→ A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced by them actually as defences against grazers and browsers.

→ Population density : The number of organisms belong to same species in a given time and habitat is called population density.
→ Four basic processes, two of which (natality and immigration) contribute to an increase in population density and two (mortality and emigration) to a decrease.
→ Natality : Natality refers to the number of births during a given period in the population that are added to the initial density.
→ Mortality : Mortality is the number of deaths in the population during a given period.
→ Immigration : Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
→ Emigration : Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

→ single individuals of any species; majority of them live in groups in a well defined geographical area, share or compete for similar resources, potentially interbreed and thus constitute a population.
→ Characteristic of population : (i) birthrate, (ii) death rate, (iii) sex ratio, (iv) age distribution, (v) population density etc.

Interspecific interactions arise from the interaction of populations of two different species.
They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both. Assigning '+' sign for beneficial interaction, '-' sign for detrimental and 0 for neutral interaction.

Species A	Species B	Name of interaction
+	+	Mutualism
-	-	Competition
+	-	Predation
+	-	Parasitism
+	0	Commensalism
-	0	Amensalism

 

Connell's elegant field experiments showed that on the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area, and excludes the smaller barnacle Chathamalus from that zone.

→ Two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting, but not otherwise.
→ More recent studies do not support such gross generalizations about competition. While they do not rule out the occurrence of interspecific competition in nature, they point out that species facing competition might evolve mechanisms that promote co-existence rather than exclusion. One such mechanism is '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 patterns.
→ Mac Arthur showed that 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.

→ Prey species have evolved various defenses to lessen the impact of predation.
→ Camouflaged: Some species of insects and
→ frogs are cryptically-colored to avoid being detected easily by the predator.
→ Some are poisonous and therefore avoided by the predators.
→ The Monarch butterfly is highly distasteful to its predator (bird) because of a special chemical present in its body.
→ Interestingly, the butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed.

→ Population growth at given time (t+1):
→ Nt+1Nt+ [(B+I)(DE)],
Where,
Nt+1 population density at a given time
Nt initial population density
B = Natality
I= Number of immigrants
D = Mortality
E = Number of emigrants