Question

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1. Compare and contrast the effects of ecosystem engineers, foundational species and keystone species on the community structure in marine systems. In your discussion, use concrete examples from marine systems we studied to illustrate how these types of species interact with one another (directly or indirectly).

Answer 1

Ecosystem Engineers:-

These are the organisms who create, modify and maintains or destroys the habitat are called Ecosystem engineers. These species puts a great impact on the species richness, and variety of species in a particular area, due to this ecosystem engineers are important in maintaining health and stability of the environment where they are living. As all organisms impact the environment they live in some or other way, the term "ecosystem engineers" is used only for keystone species whose behaviour puts a great impact on other organisms.

In marine environments, filter feeders and plankton are the ecosystem engineers because they alter the turbidity and light penetration, as well as controls the depth at which photosynthesis can occur, limiting the primary productivity of benthic and pelagic habitats, and also influences the consumption patterns among the various trophic groups.

Another example of ecosystem engineers in marine environments is scleractinian corals, they create the framework for the habitat on which many coral-reef organisms depends. So ecosystem engineers like corals helps in maintaining their environment. Parrotfish is another example they usually help in maintaining coral reefs because they feed on the macro algae which competes with the coral. As this relationship is mutually beneficial, a positive feedback cycle is formed between the two organisms, which makes them responsible for creating and maintaining the coral reef ecosystems.

Foundation species:-

Foundation species are the species, who plays a strong role in structuring a community. A foundation species can occupy any trophic level in a food web (they can be primary producers, herbivores or predators). Examples are some members of marine invertebrate and algae communities.

Foundation species play a major role in structuring a community, in many different ways. The presence of a foundation species can reduce or increase the species diversity based on its specific role in a particular ecosystem.

Example- kelp are the organisms, whose presence gives shelter and suitable habitat to many other organisms in a marine ecosystems. Kelp forests are formed by brown macroalgae.

keystone species :-

These are the species which puts a great impact on its environment when compared to its number. These species plays a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem, they also helps in determining the types and numbers of various other species in the community. A keystone species may be a plant or animal which plays a unique and crucial role in the way an ecosystem functions. Without the keystone species, an ecosystem will be different or cease to exist.

A keystone species is a predator which prevents a particular herbivorous species from eliminating a dominant plant species. If prey numbers are low, keystone predators are less abundant but effective. In absence of the predators, the herbivorous preys grows vigorously in numbers, and super-cede the dominant plants, and change the character of the ecosystem.

Sea otters protect the kelp forests from damage by sea urchins. When the sea otters of the North American west coast were hunted commercially for their fur, their numbers drastically decreased in the North Pacific Ocean by which, they were not able to control the sea urchin population. As a result the sea urchins started eating the holdfasts or root like structures of kelp, so vigorously that the kelp forests to a great extent disappeared along with all other species, which used to depend on the kelp forest. When the sea otters were reintroduced, it helped the kelp ecosystem to get restored.

So here the keystone species helped in re-establishing the foundation species, as well as they helped in maintaining the foundation species.