question_answer

(i) Discuss two major models of determining population growth.

(ii) Draw graphs and the related equations of both types of growth models.

(iii) Which out of these two is the most realistic model of growth in nature and why?

Or

All organisms on earth including plants, animals, microbes cannot live in isolation, they instead interact in various ways to form their biological community.

(i) What is protocooperation? Explain with example.

(ii) Differentiate between predation and competition with suitable examples.

(iii) Define parasitism with an example.

Answer:

(i) Two models of determining population growth are
(a) Exponential growth model Exponential growth occurs when unlimited resources (food and space) essential for population growth are present in the habitat.
(b) Logistic growth model Logistic growth occurs when limited resources are available in a habitat supporting the species present. This leads to competition among species. A population with logistic growth shows initial lag phase, then phase of acceleration, deceleration and finally an asymptote.
(ii)
(iii) Logistic growth curve is considered more realistic because the resources present in a habitat are finite.
They become limited sooner or later.
A given habitat has enough nutrients to support the maximum possible number of a species. Beyond this no further growth of population is possible. This limit is called as carrying capacity (K) for a species present in that habitat. Hence, no population can sustain exponential growth indefinitely.
Or
(a) Protocooperation is an interaction between two different species in which both are mutually benefitted but they can live without each other. It is also called facultative mutualism, e.g. sea anemone is carried from place to place by the moving crab and is benefitted by getting more places for the food.
Hermit crab may also derive benefit through camouflage and protection provided by a sea anemone because of the presence of stinging cells in the latter.
(ii) Differences between predation and competition are as follows
Predation	Competition
An interaction between two species where one (parasite) harms the other organism (host) while deriving benefits from them.	An interaction between species where both partners suffer.
Physical association occurs between predator and its host.	No physical association occurs between competitors.
e.g. tiger and deer.	e.g. in some South American lakes, vesting Flamingos and resident species compete for food.
(iii) Parasitism is the mode of interaction between two species in which one species (parasite) depends on the other species (host) for food and shelter and in this process damages the host. In this process, one organism is benefitted (parasite), while the other is being harmed (host), e.g. interaction between Cuscuta (parasite) and shoe flower bush.