The following diagrams are the age pyramids of different populations. Comment on the status of these poulations.
Figure A It is a 'pyramid' shaped age pyramid. In this figure, the base, i.e., pre-reproductive stage is very large as compared with the reproductive and post-reproductive stages of the population. This type of age structure indicate that the population would increase rapidly.
Figure B It is an 'inverted bell' shaped pyramid. In this figure, the pre-reproductive and reproductive stages are same. This type of age structure indicates that the population is stable.
Figure C It is 'urn' shaped pyramid. In this figure, the pre-reproductive and reproductive stages are less than the post-reproductive stages of this population. In this population more older people are present. This type of age structure indicates that the population definitely is declining.
$$ \text { Comment on the growth curve given below. } $$
The growth curve shown above is logistic growth curve or S-shaped curve.
Logistic growth curve is considered more realistic because unlimited resources are not available in an ecosystem or in a habitat, where
$K$-stands for carrying capacity.
$N$-indicates population density, which is the number of species of a population per unit area.
$r$-is for intrinsic rate of natural increase.
A population of Paramecium caudatum was grown in a culture medium. After 5 days the culture medium became overcrowded with Paramecium and had depleted nutrients. What will happen to the population and what type of growth curve will the population attain? Draw the growth curve.
Initially, after a lag phase, the population will grow in an exponential manner as the nutrients and space will be abundant.
When the food sources get depleted, the population density starts decreasing and ends in an asymptote phase, then the population density reaches the carrying capacity (maximum number of individuals of a population or species that a given environment can sustain indefinitely).
The population shows a pattern of logistic growth giving an S-shaped curve.
Where $K=$ carrying capacity
$N=$ population density at time ' $t$ '
$r=$ Intrinsic rate of natural increase
Discuss the various types of positive interactions between species.
The interspecific interaction are of three types positive or beneficial, negative or antagonistic and last neutral interaction.
Some positive interactions are scavenging, commensalism, protocooperation and mutualism.
Mutualism This interaction confers benefits on both the interacting species, e.g.,
(i) Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria.
(ii) The mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy-yielding carbohydrates.
(iii) Plants offer nectar, juicy and nutritious fruits to animals that help pollinate their flowers and disperse their seeds.
Commensalism This is the interaction in which one species benefits without affecting the other, e.g.,
(i) An orchid growing as an epiphyte on a mango branch.
(ii) Barnacles growing on the back of a whale.
(iii) The cattle egret foraging close to the cattle that stir up and flush out insects from the vegetation.
(iv) Sea anemone that has stinging tentacles and the clown fish that lives among them to get protection from predators.
Scavenging is the act of feeding by scavenger like bacteria, fungi on the remain of dead animals.
Protocooperation in the type of relationship in which both partners mutually obtain benefits. But they associate purely to benefit from each other and can live without each other.
In an aquarium two herbivorous species of fish are living together and feeding on phytoplanktons. As per the Gause's principle, one of the species is to be eliminated in due course of time, but both are surviving well in the aquarium. Give possible reasons.
Competition is a rivalry relationship between two or more organisms. A competition between individual of same species (intraspecific) is more acute than the competition between individual of different species as all the members in a intraspecific competition have same basic requirements like food, water, light, space, mating and shelter.
But this is true only when resources are limited. According to Gause's principle, one of the species is to be eliminated.
But studies recently have revealed that species facing intraspecific competition may evolve mechanism to pencourage co-existence rather than exclusion. This can also be done by a method known as ' resource partitioning'.