The Biotic Environment

Food is not normally an important regulator of insect abundance because other envi- 719

ronmental factors have a significant adverse effect on insect growth and reproduction. In addition, many insects are polyphagous, and larvae and adults may eat different foods. In two situations the quantity of food may be limiting: (1) when only a proportion of the total food is available and (2) when insect population density is not kept in check by other factors. The nutritional quality of food also markedly affects survival, rate of growth, and fecundity of insects.

The evolution of diverse feeding habits has allowed insects to exploit virtually all organic carbon sources. The majority of species are herbivorous and, as the prey of other animals, are key elements in the flow of energy from primary producers to second-order consumers. Others are predators, parasites, pathogens, detritus feeders (especially in aquatic ecosystems), or may enter into a variety of mutualistic relationships with plants or other insects. Through evolution complex interactions between plants and insects have developed based on the theme that insects feed on (gain energy from) plants, while plants attempt to defend themselves (conserve this energy) or obtain service (most often cross-pollination, rarely protection) from insects in exchange. Some plants protect themselves by producing toxins. However, some insects have become able to cope with these toxins and may even accumulate them for protection against predators and, possibly, microorganisms. Other insects have become adapted to feeding on parts of plants that lack toxins (spatial avoidance) or when plants have a low toxin content (temporal avoidance). To obtain effective cross-pollination: (1) plants must produce the correct amount of nectar to maintain insects' "interest," yet stimulate visits to other plants of the same species; and (2) insects must be able to recognize members of the same plant species. The quantity of nectar produced in each flower depends on factors such as number of flowers per plant, synchronous or asynchronous blooming of flowers on a plant, population density of plants (average distance between plants), air temperature when flowers are blooming, and the size and foraging capacity of the pollinators.

Interactions between insects and other animals may be intraspecific or interspecific. In-traspecific interactions include those related to underpopulation and those that result from overpopulation. Populations are generally self-regulating, that is, maintain their density within a suitable range. As a prey species' density falls, predators may experience greater difficulty in locating food and may migrate or produce fewer progeny. Thus, more prey may survive to reproduce, leading to restoration of the original population density. In some species females produce more eggs or reproduce parthenogenetically in underpopulated conditions. Overpopulation results in competition for resources such as oviposition, overwintering, and resting sites, and, occasionally, food, and renders a greater proportion of the population susceptible to predation, the effects of weather, and disease. When overcrowded, part of a population may migrate, cannibalism may increase, females may lay fewer eggs, and the rate of larval development may be reduced. Some species regulate breeding population density by territoriality.

When two species that coexist (live in the same habitat) require a common resource, they are said to compete for that resource. The more closely related are the species, the more nearly identical will be their total requirements (niche), and the greater will be the competition between the species, leading ultimately to the competitive exclusion (displacement) of one species from that habitat. To avoid displacement closely related species evolve mechanisms that make their niches sufficiently different that both can occupy the same habitat. The mechanisms include spatial segregation, microhabitat selection, temporal (diurnal or seasonal) segregation, and dietary differences.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook

Post a comment