The Biotic Environment

4.2.2. Predator-Prey Relationships

It will be abundantly clear that the distribution and abundance of a species will be greatly affected by those organisms that use it as food and that the reverse is also true, namely, that the distribution and abundance of prey will determine the distribution and abundance of predators.

Most Insecta feed on plant material in one form or another, that is, are primary consumers, and therefore play a major role in the flow of energy stored in plants to higher trophic levels. However, another large group, probably about 10% of known species, feed on other animals, especially insects. Some of these are typical predators or parasites, but the majority are parasitoids that belong especially to the Tachinidae (Diptera), Strepsiptera, and so-called "parasitic" Hymenoptera (Chapter 10, Section 7). A parasitoid may be defined as "an insect that requires and eats only one animal in its life span, but may be ultimately responsible for killing many" (Price, 1997, p. 141). Typically, a female parasitoid deposits a single egg or larva on each host, which is then gradually eaten as the offspring develops. Adult parasitoids are free-living and either do not feed or subsist on nectar and/or pollen. Thus, a parasitoid differs from a typical predator, which feeds on many organisms during its life, and a parasite, which may feed on one to several host individuals but does not kill them. However, as Price (1997) pointed out, the distinction between predator and parasitoid is not always clear. For example, a bird that captures insects as food for its offspring is comparable with a parasitoid that lays its egg on a freshly killed or paralyzed host. Further, a predator and parasitoid face the same problem, namely, location of prey (host), and may solve the problem in an identical manner. Of course, from the prey's point of view, it matters not whether the aggressor is predator or parasitoid; for either, it must take appropriate steps to avoid being eaten! In the final analysis, the population dynamics of predator-prey and parasitoid-host relationships will be identical, and it is therefore appropriate to discuss these relationships under the same heading. In the remainder of this section, therefore, the terms "predator" and "prey" should be taken to include "parasitoid" and "host," respectively, except where specifically stated otherwise.

First, what strategies are employed by prey species in order to reduce the chances of their members being eaten? Probably, the most obvious strategy is for insects to avoid detection. This they may do in various ways—by burrowing into a substrate, which frequently also serves as food, by hiding, for example, on the underside of leaves, by becoming active for a restricted period of the day, or through camouflage where their color pattern merges with the background on which they normally rest, or they precisely resemble a twig or leaf of their food plant. Other prey species have evolved other protective mechanisms that depend on initial recognition of the prey by the predator for their effectiveness. Such mechanisms include being distasteful, a feature usually accompanied by aposematic (warning) coloration so that a predator soon learns to recognize that species are distasteful. Related to this is Mullerian mimicry in which distantly related, distasteful species resemble each other, so that if a predator recognizes their pattern of coloration all species are protected. Another form of mimicry is Batesian, in which an edible species (the mimic) comes to resemble a distasteful species (the model) (Figure 9.33). The success of this method of avoiding predation relies on the probability of the predator selecting the distasteful model rather than

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