SPECIES INTERACTIONS

DOMINANCE

Not all species in anecosystem are equally important in determining the nature and function of the entire ecosystem. Every community has one or two dominant species, being the most abundant or containing the most biomass. Dominant species however may not be necessarily essential to a community. The most essential species in the ecosystem are the so-called keystone species as their activities determine the structure of the entire community and consist of species that often turn out unexpectedly to be the ones essential to the survival of the community. In communities controlled by a keystone species, its removal can have dramatic consequences whereas, in communities controlled by competition, removal of one or a few species may not be noticed.

SPECIES INTERACTIONS

The different organisms in the ecosystem each occupies a certain ecological niche, which is described as all the physical, chemical and biological factors that a species needs to live, grow and reproduce in an ecosystem.

Specialized niche - species that can tolerate only a narrow range of climatic and other environmental conditions and feed on a limited number of different plants and animals. This limits them to specific habitats in the ecosphere.

Generalist niche - adaptable organisms which can live in many different palces, e ait a wide variety of foods, and tolerate a wide range of environmental conditions. This explains why they are usually in less danger of extinction that a species with a specialized niche.
Examples of generalist species : flies, cockroaches, mice, rats and human beings.

The ecological niches of species include how they interact with other species in an ecosystem. The major types of species interaction are interspecific competition, predation, parasitism, mutualism and commensalism.

Interspecific competition happens when two or more species in the same ecosystem use the same scarce resources such as food, water, oxygen, sunlight, soil nutrients, space and shelter or anything required for survival. The most obvious form of species interaction in food chains and webs is predation. An organism of one species, known as the predator, feeds on parts or all of an organism of another species, the prey, but does not live on or in the prey. Together, the two kinds of organisms involved, such as frogs and insects, are said to have a predator-prey relationship. Another example is the picture with the lynx chasing a hare.

Another type of species interaction is parasitism. Parasites feed off another organism, called their host, but unlike predators, they live on or in the host for a good part of their life cycle. The parasite draws nourishment from and gradually weakens its host. This may or may not kill the host. Pathogens are disease-causing organisms like bacteria, viruses, or protists that could be thought of as microscopic parasites. Unlike, most parasites, however, many pathogens inflict lethal harm on their hosts. Example is the photo below of a roundworm may affect dogs and puppies.

Animals, just like humans, can become infected with parasites. Internally, contaminated water and food can spread the problem to our pets. Externally, animals become infected by parasites on their bodies, especially on their fur, because of exposure to infected animal wastes. Forgetting to wash your hands even one time after handling or cleaning up after your animal can transmit the parasite to you. Pets are a wonderful part of our lives. They provide comfort, companionship, protection, amusement, and unconditional love for their owners. Yet, pets, like humans, are often victims of serious infections that can unintentionally be passed on to their owners. In fact, there is a whole set of diseases classified as 'zoonoses' (animal-transmitted diseases) in parasitology textbooks. Animals are major carriers of parasites, and most physicians, let alone the general public, are unaware of this fact. Experts have projected that of the 110 million pet dogs and cats in this country, over half may be infected with at least one or more different kinds of parasites. Considering these numbers, the potential for transmission of parasitic infection from animals to humans is extremely high.

In some cases two different types of organisms interact directly in ways that benefit each species. Such a mutually beneficial interaction between species is called mutualism. e.g., the honeybees and birds and certain flowers. The honeybee/bird feeds on the flower's nectar and in the process picks up pollen and pollinates female flowers when it feeds on them.

Commensalism, on the other, is a type of species interaction where one type of organism benefits while the other is neither helped nor harmed to any great degree. Algae that grow on the shells of sea turtles and false clownfish hiding in anemone (photo below) are examples of this interaction.Another example, epiphytic plants (which grow on other plants but are not parasitic) gain an enormous ecological benefit from living on larger plants, because they gain access to a substrate upon which to grow relatively high in the canopy. The host trees, however, are not affected in any significant way by this relationship, even in cases when they are supporting what appears to be a large population of epiphytes. Some plants are specialized as epiphytes, for example, many species of airplants or bromeliads (family Bromeliaceae), orchids (Orchidaceae), and ferns (Pterophyta). Many lichens, mosses, and liverworts are also epiphytes on trees. There are also animal analogues of this relationship. Sometimes sea anemones will gain a benefit in terms of food availability by growing on the upper carapace of a hermit crab (crustacean infraorder Anomura) which is apparently unaffected by the presence of the epiphyte.