The study of life histories involves the full span of life, from egg or sperm through reproduction and death. The ways in which individuals maximize progeny production and survival are about as diverse as the populations and species themselves. Research interest in life history is therefore strongly comparative, looking at the variation in life-history characteristics within populations, within species and among related species. As with ecology in general, we search for patterns in nature and develop hypotheses and theories, which account for the trends that we observe, and prompt new observations in a cycle of efforts to refine knowledge.

Understanding of life histories is fundamental to insect ecology, and we have covered many examples of life-history studies already in this book, and more will follow. Behavioral traits that promote fitness were covered in Chapter 2, and the evolution of life histories of social insects was discussed in Chapter 3. Chapter 4 included discussion of wing polymorphism in planthoppers (Figure 4.5), and jousting and territoriality of Pemphigus aphids (Figure 4.11). Density effects on planthopper fecundity and wing polymorphism were involved with competition (Chapter 5, Figure 5.8), and egg-laying schedules of a fruit fly were described in Chapter 9 (Figure 9.10). We noted also in Chapter 9 the differences between pro-ovigenic and synovigenic egg production, and the marked differences in survival of progeny portrayed in survivorship curves. In Chapter 6 different strategies of yucca moths were noted among true pollinators and two classes of cheaters (Figure 6.14). We also saw divergence of life-history types in scarab beetles (Figure 6.16) and the constraints on ovariole number and fecundity of parasitoid wasps and flies (Figure 8.4). Indeed, the study of life-history traits runs throughout ecology, and this is how it should be, because understanding the evolution of whole life histories is at the heart of understanding insects, and the evolutionary pathways along which they have traveled. This point is taken up again in the last section of this chapter on applications.

Everybody is conscious of insects, and even concerned about them. In fact, we each have an ecological relationship with their kind. We share our houses and gardens with them, our walks and picnics, and our adventures. So should we not understand them? Their richness in species and interactions, their beauty and behavioral intricacy, all enrich our lives if we understand who they are, and what they are doing. Therefore, the ecology of insects is for everybody.

Eisner (2003, p. 1), in his latest book, For Love of Insects, starts by writing that “This book is about the thrill of discovery.” And, Wilson (1994, p. 191), in his autobiographical, Naturalist, advised, “Love the organisms for themselves first, then strain for general explanations, and, with good fortune, discoveries will follow. If they don't, the love and the pleasure will have been enough.” Here is sound advice from two of the greatest practitioners of entomology and ecology, for discovery is thrilling, and the deeper the fascination one develops, the greater will be the discoveries that follow.

Contents

This book concludes with discussions on the broadest biological patterns we can observe on this Earth, and the reasons for their existence. We also examine smaller scales of variation that would be seen on the landscape and ecosystem levels. In doing so we pick up various topics discussed in previous chapters, such as the roles of time and space as influences on species richness, and expand this view to the global level, showing that the same factors remain important as we scale up our perspective to interactions on Earth. We also look at the paleobiological record again, as we did in Chapter 1 to note the long evolutionary history of insects, but in this section we examine the record for clues on what might be expected as global changes occur, and if predictions are possible.

All natural populations fluctuate: they are dynamic. introduced the concepts of population growth and regulation. How and why populations change are the subjects of this chapter. Population dynamics has been of major concern in insect ecology for at least two reasons. First, ecology has been defined as the study of the distribution and abundance of species (Andrewartha and Birch 1954, Krebs 1972). Since the study of population dynamics must include both changes in numbers over time and over the landscape, the subject acts as a central theme in ecology: a unifying concept that permeates the science. It is therefore critical to the conceptual development of ecology. Second, the subject is directly applicable to problems in managing plants as resources for humans, in agriculture, horticulture and forestry. In fact, the need to monitor and understand insect damage to crops and forests was a major motivation for the beginnings of ecology and the study of population dynamics. Other applications include the study of vectors of diseases, such as mosquitoes, pests of cattle such as ticks and screwworm, and vectors of plant pathogens. For these reasons the field of insect population dynamics has played a prominent role in the development of basic ecology and in the understanding and management of serious pests over the landscape.

First we will examine major patterns in populations and then move on to mechanisms that may be driving these patterns, including abiotic and biotic influences, and complex interactions involving both. We also consider the question of how common eruptive species are, how frequently eruptions occur, and whether outbreaks result from human interference with natural dynamics. We note that long-term studies are essential in deciphering the reasons for population change, but many potential influences need to be investigated. Bottom-up effects from plants, top-down effects from natural enemies and lateral effects all need attention. Spatial distribution of populations is also important in a fragmented landscape, covered by the field of metapopulation dynamics. Population dynamics is a field of wide application for understanding pest species, epidemiology, biological control and conservation, all requiring information for planning and management.

Contents

Behavior links the organism to its environment. At every moment of the day and night behavioral responses to environmental cues, and internal drives, guide an individual through its often perilous existence. Behavior determines success or failure in the efforts to reproduce. Discovering the many cues that insects use to inform them of their environment, and their responses to these stimuli, is an ongoing pursuit of behavioral ecologists. This is because insects can be much more specialized than humans in the cues employed to locate food, and cues that stimulate feeding. Indeed, the ways in which they relate to their surroundings is often notably different from we humans. As a result, behavioral ecology is a broad and fascinating subject which reaches well beyond this section of the book, into on species interactions and other parts of the book.