Question

If you can’t answer both I would rather you answer number 2 then. Thank you :)

1) What is parasite-mediated apparent competition and how does it differ from classical competition?

2) Species A is the indigenous population on an island nation.  Species B was introduced to this island 200 years ago and shares the same habitat as species A.  During the ensuing 200 years since species B was introduced, and in the face of a growing human population, the population of species B has proliferated.  Species A by comparison is declining.  There is evidence of hunting pressure on the two species as well as a shared pathogen that infects both species.  Explain the type of competition that might be present in the ecosystem shared by the populations of these two species and how this type of competition may be affecting changes in the two populations (e.g. species A and species B).  In your explanation please indicate which species may be a generalist in this system.  If there are two other species in this island that interact with the populations of species of A and B how might the entire host of communities be affected if the population of species A is declining if one of those two species preys on species A.  We discussed parasites/pathogens influencing population growth and being able to regulate population growth in a density-dependent manner.  What are different effects that a parasite/pathogen might have in population regulation (e.g. think about the lynx/hare/worms).

Answer 1

1. Parasite-mediated competition - When a parasite affect the competitive interaction between two species, then it is known as parasite-mediated competition. Parasitism of prey species alter the interactions of associated predators, their own prey, and other prey of predators

For example-

There are two lizard species on Caribbean island- Anolis gingivinius and Anolis wattsi. Out of these two, A. gingivinius is a better competitor than A. watti. But on the same side, Anolis gingivinius is more susceptible to the parasitic effect of malarial parasite Plasmodium azurophilum. While Anolis wattsi. Remains unaffected by Plasmodium azurophilum. Thus, in such scenario the two species of lizard will live together only when the parasite is present as it lowers the competitive ability of A. gingivinius'. It also prevents competitive exclusion thereby maintaining species diversity in this ecosystem

In normal Parasitism, only two species are affected – one that benefits from the other and second one that is harmed.

2. The competition between species A and B is known as interspecific completion that occur between organisms of two different species competing for similar resources and exposed to similar threats. The population of species A is declining because of following probable reasons-

a) Pathogen may be more deleterious for species A than species B, thereby survival rate of species B higher than species A.

b) Hunting rate for species A is higher than species B

c) Species B is more fit as compared to species A and hence can survive efficiently to the changing environmental conditions.

The species B (which is proliferating) is a generalist species that can survive in wide variety of environmental conditions along with making use of different resources for survival.

Now in case if there are two more species interacting with species A and B in a way that one of these new species preys on species A, then with declining population of species A, the population of dependent species (one of out of the two new species) shall decrease. This will pave way for both species B and the newly introduced second species to grow in number in absence of competition.

Parasites regulate population in following ways –

a) Restricting growth of invasive species and allowing flourishing of other beneficial species.

b) Regulating the spread of disease in any organism by reducing its population