Insects play significant roles in the ecology of the world due to their vast diversity of form, function and life-style; their considerable biomass; and their interaction with plant life, other organisms and the environment. Since they are the major contributor to biodiversity in the majority of habitats, except in the sea, they accordingly play a variety of extremely important ecological roles in the many functions of an eco-system. Taking the case of nutrient recycling; insects contribute to this vital function by degrading or consuming leaf litter, wood, carrion and dung and by dispersal of fungi.
Insects form an important part of the food chain, especially for entomophagous vertebrates such as many mammals, birds, amphibians and reptiles. Insects play an important role in maintaining community structure and composition; in the case of animals by transmission of diseases, predation and parasitism, and in the case of plants, through phytophagy and by plant propagation through pollination and seed dispersal. From an anthropocentric point of view, insects compete with humans; they consume as much as 10% of the food produced by man and infect one in six humans with a pathogen.
Community ecology is the process by which a group of organisms which live in the same location interact. There is direct interaction, which takes the form of symbiosis, competition and predation, which are the most easily notable. There is also indirect interaction, such as reproduction, foraging patterns and decaying. Every organism is at its most basic state could be a consumer in some situations, and a producer in others. The culmination of all these interactions is what defines a community and what differentiates one from another. Insects often play several roles in these communities, though these roles vary widely based on what species is present.
Decomposer insects are ones that feed on dead or rotten bodies of plant or animal life. These insects are called saprophages and fall into three main categories; those that feed on dead or dying plant matter, those that feed on dead animals (carrion), and those that feed on excrement (feces) of other animals. As dead plants are eaten away, more surface area is exposed, allowing the plants to decay faster due to an increase in microorganisms eating the plant. These insects are largely responsible for helping to create a layer of humus on the soil that provides an ideal environment for various fungi, microorganisms and bacteria. These organisms produce much of the nitrogen, carbon, and minerals that plants need for growth. Carrion feeders include several beetles, ants, mites, wasps, fly larvae (maggots), and others. These insects occupy the dead body for a short period of time but rapidly consume and/or bury the carcass. Typically, some species of fly are the first to eat the body, but the order of insects that follows is predictable and known as the faunal procession. Many dung beetles and manure flies are attracted to the smell of animal feces. The adults often lay eggs on fresh excrement and the larvae will feed on the organic matter. Many species of dung-feeders have evolved so they will only feed on feces from a specific species. There is even a type of dung-beetle that will roll feces into a ball, push it into a pre-dug hole, laying an egg in that dung and then cover it with fresh dirt to provide a perfect nursery for their larvae.
Carnivorous insects survive by eating other living animals, be it through hunting, sucking blood, or as an internal parasite. These insects fall into three basic categories: predators, parasites, and parasitoids. Predatory insects are typically larger as their survival is dependent upon their ability to hunt, kill/immobilize, and eat their prey. There are several exceptions to this though, with ants being the most notable. Ants, and other colony insects, can use their sheer numbers to overwhelm their prey even if the ants are significantly smaller. They often have specialized mandibles (mouth parts) for this task, some causing excruciating pain, paralysis, or simply having a high bite force. The insects who live on their own though, must be able to reliably bring down their prey and as such have developed a myriad of unique hunting methods. Some actively travel, seeking out their prey while others wait in an ambush. Others may release chemicals to attract specific creatures and others still will eat anything they can. Parasites infest the victim’s body and eat it from the inside out. The presence of the parasite is often not noticed by the host as the size discrepancy is typically so vast. Parasites vary widely in how they survive in their host, some complete their full life cycle within the body while others may only stay in for the duration of their larval stage. There is as great of variation in methodology and species in parasites as in any other type of insect even if it may not seem so at first. The most threatening parasites to humans though, are ones that live outside the host and consume the hosts blood. These species transmit virus, disease, and even other, smaller parasites to the host, spreading these throughout the populations of many third world countries with poor health care. A subcategory of parasites, called parasitoids, is one that feeds on the host body so much so that the host is eventually eaten. One species of wasp, the spider wasp, will paralyze spiders before bringing them back to their nest and injecting it with a wasp larvae. The larvae will eat its way out, secreting a numbing and paralyzing agent until there is nothing left of the spider other than the exoskeleton then go through a metamorphism and become an adult wasp.
Herbivores are insects that feed on living plant matter or the products of a plant. These insects may eat essential parts of the plant, such as the leaves or sap, or they may survive on the pollen and nectar produced by the plant. Herbivorous insects often use olfactory or visual cues to determine a potential host plant. A visual cue could simply be the outline of a certain type of leaf, or the high contrast between the petals of a flower and the leaves surrounding it. These are typically associated with the olfactory signal an insect may receive from their intended meal. The olfactory que could be the scent of the nectar produced by a flower, a certain chemical excreted to repel unwanted predators, or the exposed sap of a cherry tree. either of these two senses could be the driving force behind an insect choosing to consume a certain plant, but it is only after it takes the first bite, and the confirmation of this food is made by its sense of taste, that it truly feeds. After a herbivorous insect is finished feeding on a plant, it will either wait there until hungry again, or move on to another task, be it finding more food, a mate, or shelter. Herbivorous insects bring significantly more danger to a plant than simply that of consumption, they are among the most prominent disease carrying creatures in the insect world. There are numerous diseases, fungi, and parasites that can be carried by nearly any herbivorous insect many of which fatal to the plant infected. Some diseases even produce a sweet smelling, sticky secretion from the infected plant to attract more insects and spread farther.
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