The Living World - Environmental Science - page 34

specific environment and are very good at their role within that niche, but this makes the species more vulner-
able to any type of change.
Species Interactions
In ecosystems, organisms interact with other organisms in a variety of ways. Interactions can lead to positive or
negative effects on the organisms involved. These interactions include competition, mutualism, predation,
parasitism, herbivory, commensalism, and amensalism.
Competition is the process by which organisms vie for the same resources, resulting in one outperforming the
other. Resources over which competition occurs include food, water, shelter, mates, and sunlight. When two or
more different species compete, it is called interspecific competition. When individuals of the same species
compete, the situation is called intraspecific competition . When organisms are in competition, generally each
has a negative impact on the other, since one will outcompete the other for the resource. In some situations,
though, species adapt to competition over time through evolution. The result is that each species reduces com-
petition with others by sharing a resource but using it differently or by using somewhat different resources to
fulfill its needs. This is called resource partitioning.
In mutualistic interactions, two or more species benefit from one another, each helping the other. For ex-
ample, bees and flowers help one another. The bees take nectar and pollen from the flowers for food while also
assisting with the spreading of pollen from one flower to another. Neither organism is harmed during their in-
teractions. Another example is lichens, which are made up of fungi and algae living together in a symbiotic re-
lationship. The fungi provide shelter for the algae, and the algae provide food for the fungi through their photo-
synthetic abilities. Lichens are also an important pioneer species.
During predation, one species hunts, captures, kills, and consumes another species, resulting in the second
species' instant demise. One species benefits and the other is harmed. This is a predator/prey relationship. Be-
cause this relationship is how energy is transferred throughout the trophic levels of ecosystems, most predators
are also prey at some point. This relationship contributes to the dynamics of a population. The more prey there
are, the greater number of predators that can be supported. More prey supports an increase in the number of
predators, but at some point the population of predators will meet its carrying capacity and will start to decline.
The prey population will eventually begin to increase again once the predators decline, keeping the predator/
prey cycle in motion.
With parasitism, one organism uses another for food and nutrients while also harming the other individual.
The parasite is the organism that benefits, and the host is the organism that is harmed. The damage usually is
not immediate but occurs over a period of time. Parasites can live in a variety of places relative to their hosts.
Some live inside their hosts, others live on their exterior, and still others live on their own and meet their hosts
only sporadically. Often, parasites and hosts will evolve relative to each other in a process called co-evolution.
When plants are consumed by animals, the process is termed herbivory. In this interaction, the plants' growth
and reproduction are affected, while the animals benefit from the nutrients the plants provide. The most com-
mon herbivores are insects. In many cases, plants produce defenses—such as toxins, thorns, or hairs—to dis-
courage herbivorous consumers.
Commensalism is the process by which one species benefits from their relationship and the other species is
neither positively nor negatively affected. For example, cattle egrets are often seen around cattle, standing on
their backs and on the ground around them. The egrets benefit because the cattle's movements stir up insects on