The Biology of Deserts. David Ward. 2009. Oxford University Press, Great Clarendon Street, Oxford, OX2 6DP, UK. 304 pages with 135 line and 90 black-and-white illustrations. $55.00, Paperback. ISBN 978-0-19-921147.
The book gives a concise introduction to the ecology of deserts. Deserts are widespread on Earth and are defined by their arid conditions and not by their temperatures. Rainfall can vary widely from 0 to 500 (20 inches) mm among deserts, but 250 mm (10 inches) of rainfall often is considered as an upper limit by some scientists. Temperatures of deserts vary from below 0 °C (32 °F) to over 50 °C (122 °F) and definitely affect desert ecology. The book includes a wide range of ecological and evolutionary issues affecting the adaptations and interactions of desert plants and animals. The author notes that the simplicity of desert ecosystems makes them amenable for biological studies.
The book has 11 chapters. The introduction covers general topics of creation and age of deserts and indexes of aridity. It is noted that most deserts lie between the Equator and Tropics of Cancer and Capricorn. The second chapter covers abiotic factors. Precipitation and water are addressed with discussions of amount and temporal distribution of rainfall, desert fog, runoff, soil salinity, and oases. The effects of sandy land and rocky land are contrasted with respect to effects on the desert environment. Short presentations are made for hot deserts and cold deserts and of the effects of fires on deserts. Geology of deserts with respect to landscapes of different types—sand, stone, rock, plateau, and mountain—is discussed. It is noted that only about 15% to 20% of deserts have sand landscapes. The third chapter addresses morphological and physiological adaptations of desert plants. Species are classed as drought-escaping plants that grow only when water is available; drought-evading plants that have deep roots, succulence, or morphology or metabolic processes (e.g., crassulacean acid metabolism, C-4 photosynthesis) that allow for survival; drought-enduring plants that lose leaves during drought; and drought-resisting plants that have stomates that close and other morphological features that help to ensure maintenance of turgor. An alternative classification system based on the strategies that plants use to protect growing points is reviewed also. The chapter continues with details on adaptations of plants to the desert environment. The fourth chapter covers morphological, physiological, and behavioral adaptations of desert animals. Animals must be able to withstand the lack of water and the high or low temperatures to survive in deserts, using strategies of evading or enduring the adverse temperatures. Most of the discussion covers withstanding the heat. Evaders are animals that avoid the heat, and endurers tolerate the heat. Evaporators are a third class of animals that cool by evaporation of water from their bodies. Size of the animals is important in the strategy employed, with small animals generally being evaders or evaporators and large animals generally being endurers. The chapter discusses the strategies with regards to specific types of animals.
The next several chapters cover plant–animal interactions and the development of communities in deserts. The fifth chapter covers competition in desert plant and animal communities and discusses responses to availability of resources, density of organisms, priority of entrance into the system among other biotic factors controlling the structure of desert communities. The importance of predation and parasitism in structuring desert ecosystems is the subject of the sixth chapter. Animals are the subject of this presentation. The author describes how mortality and risk are affected by spatial homogeneity that provides protection to predator and prey and by sensitivity of predators to their own predators. Several cases of individual animal species are discussed. Parasites are discussed with respect to the effect that parasitism has on animals. Chapter 7 covers plant–animal interactions in the desert. The chapter begins with herbivory. Spatial and temporal variability in rainfall and other water resources result in variable plant availability and abundance to herbivores. This wide variability in space and time is thought to limit the impacts of animals on plants in deserts. The chapter also discusses the importance of animals in pollination and seed dispersal and predation. Examples of interaction of plants and animals are presented. Desert food webs are covered in the eighth chapter. Models or laws to describe interactions are presented. The effects of precipitation, nutrients, and disturbances on ecosystem ecology are discussed.
Chapter 9 covers the biodiversity and biogeography of deserts. Most desert vegetation is considered to be contracted vegetation that exploits the water resources close to ephemeral rivers (wadis or arroyas) with rainfall below 70 mm annually. Diffuse vegetation occurs with rainfall above this value. Diversity of species richness, mostly with annual plants, can be very high in deserts and depends on the seasonal distribution of rainfall in particular. Animal diversity and geographic distribution is discussed with respect to ecological factors and community structures.
Human impacts and desertification are covered in Chapter 10. The author notes that deserts may or may not show negative impacts of heavy use by humans. Much attention is given to desertification or to the increase in desert lands. The author notes that desertification usually is caused by human intervention through global climate change, soil salinization, harvesting of plants for fuel and housing, and improper cropping or grazing and describes the contribution of each of these factors. Effects of military maneuvers, aquifer pumping, and oil extraction are assessed.
The last chapter addresses conservation of deserts. This chapter seems somewhat unfocused but emphasizes that deserts offer superb laboratories for the study of evolution. Additional reasons to conserve deserts are their unique features, their ecological benefits, and their pristine conditions.
This book will be of interest to horticulturists and ecologists who are interested in the biology of habitats.