Predation in Vertebrate Communities: The Bialowieza Primeval Forest as a Case Study. - Recipe - book reviews

Jedrzejewska, Bogumita, and Wlodzimierz Jedrzejewski. 1998. Ecological Studies. Volume 135. Springer-Verlag, New York. x + 450 p. $189.00, ISBN: 3-540-64138-6 (acid-free paper).

Despite virtually a century of study, we still have difficulty delineating the role of predators in altering prey populations. Many ecologists would suggest that predators actually play a minor role in structuring communities relative to abiotic phenomena. This is, however, a controversial issue that has seen a tremendous amount of research and has broad implications. Therefore, asking what seems like a simple question-how much do predators matter to prey populations?does not result in a simple answer. Rather, it unearths additional questions. For instance, do predators kill prey that would otherwise die for reasons such as limited resource availability or inclement weather (compensatory mortality) or is morality from predators additional to these other sources of mortality (additive mortality)? Does the percent of prey taken increase with increasing prey availability (density dependent predation), is it stable over wide ranges of prey densities (density independent predation), or does it actually decline with increasing prey numbers (depensatory predation)? Do predators alter prey population dynamics (population regulation, which requires density dependent predation) or do they simply harvest the population while having little influence on its dynamics (population limitation) which are driven by other factors?

One reason our understanding of these questions and of predator-prey dynamics as a whole has not advanced more rapidly is that most studies have examined one predator - one prey systems. A more realistic understanding of the importance of predation in a community is likely to come when researchers focus not on a small selection of predators and prey, but rather on entire communities of predators and prey. That time is now arriving. In this important study, Jedrzejewska and Jedrzejewska examine the dynamics of more than 30 mammalian Carnivora and birds of prey in the orders Falconiformes, Accipitriformes, and Strigiformes, as well as their respective prey, which range from ungulates to songbirds to earthworms. I am aware of no other work of similar scope. This is not a short-term work; the authors have been studying the vertebrate predator-prey community at Bialowieza Forest on the Polish-Belarussian border for over a decade and incorporate data sets of over a century in length for several species. Much of these data comes from a Polish, Russian, and Belarussian literature that many ecologists may be unfamiliar with.

Bialowieza Forest is a marvelous place, with an intriguing history of preservation. This 1500 [km.sup.2] woodland is perhaps the best-preserved temperate deciduous and mixed forest in the European lowlands. About a third of the forest is old growth and it remains contiguous with extensive forests to the north, south, and east. The fauna is virtually complete relative to what was found there a millennium ago. Bialowieza owes much of its preservation to its status as crown land, dating at least to the 15th century and the reign of King Wladyslaw Jagiello of the Polish-Lithuanian Commonwealth. By the early 1500s there was a strong local administration and guards whose primary responsibilities were to watch for bison and other large game, control timber exploitation, and organize monarchial hunts, settled in small villages around the forest. The 1800s brought the loss of Polish independence to Russia and increased exploitation of timber and game. Nonetheless, it wasn't until the retreat of the Tsar in 1915 before the invading German army that large-scale changes commenced. By 1919 bison were extinct in the forest (since reintroduced) and industrial clear-cutting of timber commenced. Large-scale forestry was continued after the war, and some small-scale forestry continues today. At the core of the forest, however, is Bialowieza National Park, an UNESCO Man and Biosphere Reserve and World Heritage Site.

The take-home message from this book is that the overall role of predation is typically far less important than other factors such as resource availability and abiotic conditions. Of course there are some exceptions to this generalization. For example, predation by wolves and lynx were the most important explanatory variable for red deer and roe deer numbers, respectively. Nonetheless, it is clear from the analyses presented in this work that the densities of most prey species are a function of temperature, snow cover, and food availability, not predator numbers. For instance, wild boar numbers and population growth rates are almost entirely a function of population size, acorn crops, and temperature. Especially intriguing is the finding that predation may be very important some years, but of minor importance in others and that effects of predators were greater during periods of decreased resource availability and population decline. This was the case for rodents. Yet predators were unable to regulate prey densities or greatly alter patterns of prey population dynamics.