Insect Diversity

However, such ecosystems did not apparently favor fossilization, and their insect fauna is practically unknown.

Toward the end of the Carboniferous and extending through the Permian periods significant climatic changes occurred that had a maaor effect on insect evolution. The Northern Hemisphere became progressively drier, extensive glaciation took place in the Southern Hemisphere, and many mountain ranges were formed, leading to distinct climatic zones and major alterations in plant and insect biota. Among the significant floral changes were the more restricted distribution or even extinction of many of the Carboniferous groups and their replacement by gymnosperms. These biogeographic changes created not only new habitats but also barriers that prevented gene flow among populations so that a veritable insect population explosion occurred, especially of endopterygotes, the class reaching its peak diversity in the Permian (Kukalova-Peck, 1991). However, near the end of this period, most of the Paleozoic orders (including many "experimental" side groups) became extinct, to be replaced by representatives of the modern orders. The reasons for the Great Permian Extinction remain obscure. Some authors suggest that a major catastrophe occurred, for example, the earth being struck by a very large meteorite or comet, while others believe that climatic changes were the cause (Erwin, 1990; Peck and Munroe, 1999).

In the Triassic and early Jurassic the gradual radiation of the extant orders continued but was largely overshadowed by evolution of the reptiles. The latter occurred in such large numbers and in such a variety of habitats that the Triassic period is generally known as the "Age of Reptiles." Many of them were insectivorous, and this may have acted as a selection pressure favoring small size (miniaturization), which is a general feature of fossil insects from this period. An alternative explanation for miniaturization has come from examination of the flight musculature across a range of insect groups, which suggests that asynchronous flight muscle evolved at this time. Asynchronous flight muscle is a prerequisite for the high wing-beat frequencies seen in the majority of good fliers (Chapter 14, Section 3.3.4). However, because wing-beat frequency is inversely proportional to body size, miniaturization was also necessary to achieve these high wing-beat frequencies (Dudley, 2001).

Early in the Triassic period the first bisexual flowers appeared. The occurrence together of male and female structures immediately led to the possibility of a role as pollinators for insects that fed on the reproductive parts of plants. Because of the risk of having their reproductive structures eaten, these early plants probably produced a large number of small ovules and much pollen (Smart and Hughes, 1973). The insect fauna of the Triassic period still included "orthodox" plant feeders such as Orthoptera and some Coleoptera, plant-sucking Hemiptera, and predaceous species (Odonata and Neuroptera). However, there were also large numbers of primitive endopterygotes, mostly belonging to the panorpoid complex, Hymenoptera, and Coleoptera, which as adults were mandibulate and therefore were potential "mess-and-soil" pollinators (Smart and Hughes, 1973).

By the middle of the Jurassic period the decline of the reptiles had begun and the earth's climate had become generally warmer. As a result the insect fauna increased both in mean body size and in variety. A good deal of mountain formation occurred at the end of the Jurassic, creating new climatic conditions in various parts of the world including, for the first time, winters. It was also about this time that the ancient world continent Pangea began to break apart and form the modern continents with their distinct insect faunas.

The Cretaceous period was an important phase in the evolution of insects, for it was during this time that adaptive radiations of several endopterygote orders took place. In

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