▪ Abstract Deer have expanded their range and increased dramatically in abundance worldwide in recent decades. They inflict major economic losses in forestry, agriculture, and transportation and contribute to the transmission of several animal and human diseases. Their impact on natural ecosystems is also dramatic but less quantified. By foraging selectively, deer affect the growth and survival of many herb, shrub, and tree species, modifying patterns of relative abundance and vegetation dynamics. Cascading effects on other species extend to insects, birds, and other mammals. In forests, sustained overbrowsing reduces plant cover and diversity, alters nutrient and carbon cycling, and redirects succession to shift future overstory composition. Many of these simplified alternative states appear to be stable and difficult to reverse. Given the influence of deer on other organisms and natural processes, ecologists should actively participate in efforts to understand, monitor, and reduce the impact of deer on ...

https://www.kora.ch/malme/05_library/5_1_publications/C/Cote_et_al_2004_Ecological_impacts_of_deer_overabundance.pdf

Ecological Impacts of Deer Overabundance

▪ Abstract In large-herbivore populations, environmental variation and density dependence co-occur and have similar effects on various fitness components. Our review aims to quantify the temporal variability of fitness components and examine how that variability affects changes in population growth rates. Regardless of the source of variation, adult female survival shows little year-to-year variation [coefficient of variation (CV 30%). Old females show senescence in both survival and reproduction. These patterns of variation are independent of differences in body mass, taxonomic group, and ecological conditions. Differences in levels of maternal care may fine-tune the temporal variation of early survival. The immature stage, despite a low relative impact on population growth rate compared with the adult stage, ma...

https://www.jstor.org/stable/pdfplus/221737.pdf

Temporal Variation in Fitness Components and Population Dynamics of Large Herbivores

Mammalian carnivores are particularly vulnerable to extinction in fragmented landscapes1, and their disappearance may lead to increased numbers of smaller carnivores that are principle predators of birds and other small vertebrates. Such ‘mesopredator release’2 has been implicated in the decline and extinction of prey species2,3,4,5,6. Because experimental manipulation of carnivores is logistically, financially and ethically problematic6,7, however, few studies have evaluated how trophic cascades generated by the decline of dominant predators combine with other fragmentation effects to influence species diversity in terrestrial systems. Although the mesopredator release hypothesis has received only limited critical evaluation8 and remains controversial9, it has become the basis for conservation programmes justifying the protection of carnivores6. Here we describe a study that exploits spatial and temporal variation in the distribution and abundance of an apex predator, the coyote, in a landscape fragmented by development. It appears that the decline and disappearance of the coyote, in conjunction with the effects of habitat fragmentation, affect the distribution and abundance of smaller carnivores and the persistence of their avian prey.

Mesopredator release and avifaunal extinctions in a fragmented system

The manner in which terrestrial ecosystems are regulated is controversial. The "top-down" school holds that predators limit herbivores and thereby prevent them from overexploiting vegetation. "Bottom-up" proponents stress the role of plant chemical defenses in limiting plant depredation by herbivores. A set of predator-free islands created by a hydroelectric impoundment in Venezuela allows a test of these competing world views. Limited area restricts the fauna of small (0.25 to 0.9 hectare) islands to predators of invertebrates (birds, lizards, anurans, and spiders), seed predators (rodents), and herbivores (howler monkeys, iguanas, and leaf-cutter ants). Predators of vertebrates are absent, and densities of rodents, howler monkeys, iguanas, and leaf-cutter ants are 10 to 100 times greater than on the nearby mainland, suggesting that predators normally limit their populations. The densities of seedlings and saplings of canopy trees are severely reduced on herbivore-affected islands, providing evidence of a trophic cascade unleashed in the absence of top-down regulation.

/pdf/ecological-meltdown-in-predator-free-forest-fragments-2fmonbx145.pdf

Ecological Meltdown in Predator-Free Forest Fragments

Monitoring programmes are being used increasingly to assess spatial and temporal trends of biological diversity, with an emphasis on evaluating the efficiency of management policies. Recent reviews of the existing programmes, with a focus on their design in particular, have highlighted the main weaknesses: the lack of well-articulated objectives and the neglect of different sources of error in the estimation of biological diversity. We review recent developments in methods and designs that aim to integrate sources of error to provide unbiased estimates of change in biological diversity and to suggest the potential causes.

Monitoring of biological diversity in space and time

West Nile virus, an Old World flavivirus related to St. Louis encephalitis virus, was first recorded in the New World during August 1999 in the borough of Queens, New York City. Through October 1999, 62 patients, 7 of whom died, had confirmed infections with the virus. Ornithophilic mosquitoes are the principal vectors of West Nile virus in the Old World, and birds of several species, chiefly migrants, appear to be the major introductory or amplifying hosts. If transovarial transmission or survival in overwintering mosquitoes were the principal means for its persistence, West Nile virus might not become established in the New World because of aggressive mosquito suppression campaigns conducted in the New York area. However, the pattern of outbreaks in southern Europe suggests that viremic migratory birds may also contribute to movement of the virus. If so, West Nile virus has the potential to cause outbreaks throughout both temperate and tropical regions of the Western Hemisphere.

/pdf/migratory-birds-and-spread-of-west-nile-virus-in-the-western-2y9738wup3.pdf

Migratory birds and spread of West Nile virus in the Western Hemisphere.

The science of overabundance : deer ecology and population management

-Population declines have been reported for nearly one-third of all Nearctic migrant birds that winter in the Neotropics. Speculative explanations for these reports have been presented emphasizing the importance of events occurring during one portion of the annual cycle versus another. These explanations are difficult to test directly. However, certain predictions can be made regarding the characteristics of populations controlled by breedingground factors as opposed to those associated with migration or wintering-ground phenomena. These characteristics can be measured for and tested experimentally on a species-byspecies basis. We present 14 such predictions, and review data currently available to assess their relevance to observed declines. Based on these data, populations of many species of Nearctic migrants appear to be controlled by wintering-ground events. Received 30 September 1993, accepted 5 January 1994. DECLINES IN AT LEAST 109 species of Nearctic migrants have been reported by one or more survey methods (Droege and Sauer 1989, Morton and Greenberg 1989, Terborgh 1989, Robbins et al. 1989a, Askins et al. 1990, DeGraaf and Rappole in press). These figures are cause for concern despite conflicting regional population trends (Sauer and Droege 1992), and despite arguments that at least some purported evidence of decline may be the result of procedural errors (e.g. survey design and analysis flaws; Hutto 1988, James et al. 1990, 1992, Rappole et al. 1993a). If the declines are real, what are the

Cause and effect in population declines of migratory birds

We monitored 42 radio-tagged, fledgling Wood Thrushes (Hylocichla mustelina) to investigate movement and habitat use during the postfledging period Fledglings' mean (± SE) age at dispersal from the natal sites was 325 ± 06 days post hatching First dispersal sites were located 15 ± 03 km from the natal site All young joined flocks of juveniles, except three birds that remained solitary Sixteen birds stayed at the first dispersal site until departure on migration, whereas nine visited additional dispersal sites On 40 occasions, 15 fledglings moved up to 6 km from their dispersal sites Before late August, 967% of fledglings' locations occurred in: (1) second growth scrub/deciduous sapling sites located along forest borders and abandoned farms (594%), (2) gypsy moth (Lymantria dispar) damaged deciduous forest (244%), and (3) Virginia pine (Pinus virginianus) forest with heavy deciduous understory (128%) Fruiting trees and shrubs used as food sources by juveniles fruit earlier in these habitats After late August, an increased number of fledgling locations (141%) occurred in mature deciduous or mixed forest, possibly tracking the later fruiting cycles of understory plants in these habitats Twenty-four of 33 fledglings left the study area in September Mean age at departure was 81 ± 5 days post hatching We suggest that postfledging movements in Wood Thrushes are keyed by the availability of food resources and the presence of conspecifics, although other factors may play a role We conclude that successful conservation of migratory species requires protection of habitats used during the postfledging period as well as those used during the nesting portion of the life cycle

/pdf/wood-thrush-postfledging-movements-and-habitat-use-in-3m7b18xbc3.pdf

Wood thrush postfledging movements and habitat use in Northern Virginia

Deer densities in forests of eastern North America are thought to have significant effects on the abundance and diversity of forest birds through the role deer play in structuring forest understories. We tested the ability of deer to affect forest bird populations by monitoring the density and diversity of vegetation and birds for 9 years at eight 4-ha sites in northern Virginia, four of which were fenced to exclude deer. Both the density and diversity of understory woody plants increased following deer exclosure. The numerical response of the shrubs to deer exclosure was significantly predicted by the soil quality (ratio of organic carbon to nitrogen) at the sites. Bird populations as a whole increased following exclosure of deer, particularly for ground and intermediate canopy species. The diversity of birds did not increase significantly following exclosure of deer, however, primarily because of replacement of species as understory vegetation proceeded through successional processes. Changes in understory vegetation accounted for most of the variability seen in the abundance and diversity of bird populations. Populations of deer in protected areas are capable of causing significant shifts in the composition and abundance of bird communities. These shifts can be reversed by increasing the density and diversity of understory vegetation, which can be brought about by reducing deer density.

John H. Rappole

Papers

Migratory birds and spread of West Nile virus in the Western Hemisphere.

The science of overabundance : deer ecology and population management

Cause and effect in population declines of migratory birds

Wood thrush postfledging movements and habitat use in Northern Virginia

Managing the Abundance and Diversity of Breeding Bird Populations through Manipulation of Deer Populations