B.13A-Interdependence_onlevel – 03

A bird builds a nest high in a tree as a safe space for eggs and young. The high location is hidden by branches and leaves. This location protects the eggs and young. The bird uses twigs from the tree to build the nest and seeds to feed the young. The birds benefit greatly from this interaction with the tree. The small, lightweight nest does not impact the tree. The tiny number of twigs and seeds taken by the bird does not interfere with the tree’s photosynthesis.

There is also no harm to the structure of the tree. Nor does the tree benefit. There are some interactions between species in which one species benefits from the interaction, while the other species is not impacted. This relationship is known as commensalism. Another benefit might be transportation, such as the pseudoscorpion hitching a ride on the leg of a much larger fly. The overall influence of commensalism is a preservation of biodiversity. This is a positive influence on the stability of the ecological community.

Species interact with each other when they share the resources in an ecosystem. The organisms need the resources to grow, reproduce, and survive. Because the resources are limited, the species are in competition with each other for those resources. Competition may occur between different species. Competition also occurs between organisms of the same species. Various species of weeds compete with grass in a lawn. The weed species can completely take over the lawn. Grass growing under a tree is sparce and thin due to competition for light between the grass and tree. When planted too closely, trees might not grow to their full size. Plants compete for nutrients, space, water, and sunlight. Competition can lead to the decline of one or both species. The decline may lead to reduced growth and lower reproductive rates. Over time, competition may lead to the extinction of a species. This loss of diversity in the community may lead to a loss in ecosystem stability. However, as the better competitors remain and reproduce, the genes that are advantageous to survival are passed on to offspring.

There are some ecological relationships between two species in which one member benefits by living in or on the other host member, causing direct harm to the host. This relationship is known as parasitism. The parasite will keep the host alive for days or years because it is gaining some benefit in keeping the host alive. Parasitic relationships are extremely common in insects. Many insects deposit their eggs within the body of another insect species’ larva. When the eggs hatch, the parasitic young kill and eat the larva, gaining nutrients from it. Humans are hosts to many parasites that cause infectious diseases, such as bacteria, fungi, viruses, and worms. Many of the same parasites in humans also invade other small mammals and birds. Wheat, fruit, and vegetable plants can be invaded by several different species of fungi. Parasites can directly regulate host populations within a community, generally without causing extinction. This has a positive impact on ecosystem stability. In addition, this allows inferior species to coexist with dominant species, which keeps biodiversity within the community intact.

There is another interaction that involves a species that benefits while another is harmed. In this interaction called predation, the predator pursues, captures, and kills its prey. Predators are highly adapted to hunting and killing. They have strong bodies, swift movement, and heightened senses. Predators may be solitary hunters, such as a snake killing small rodents or a large fish feeding on smaller fish. Solitary predators are generally larger than their prey. Other predators can be group hunters. This can be advantageous when the prey is much larger than the predator. This is seen with lions hunting large buffalo or orcas pursuing the much larger sperm whale.

The predator-prey relationship is a mechanism for population control in an ecosystem. A large predator population can eventually lead to a decline in prey population. This can lead to food scarcity for the predators, which can result in the death of many predators. With a low predator population, the prey population will rebound, and the population cycle repeats. A stable ecosystem can rebound from stresses on the populations.

Amira has learned that almost every species of living thing has a close relationship with another living thing. A stable ecosystem deviates very little from its average state. Following a disturbance, a stable ecosystem is resilient and can return to its average state. A large variety of species is important to buffer losses in a community. Relationships, such as predation, parasitism, commensalism, mutualism, and competition, can influence ecosystem stability.