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K J Gaston

Publications and source records attributed to K J Gaston.

11 recordsLinked to original sources
PubMed2002

Persistence and vulnerability: retaining biodiversity in the landscape and in protected areas.

An objective of biodiversity conservation activities is to minimize the exposure of biodiversity features to threatening processes and to ensure, as far as possible, that biodiversity persists in the landscape. We discuss how issues of vulnerability and persistence can and should be addressed at all stages of the conservation planning and implementation process. Procedures for estimating the likelihood of persistence and for measuring degrees of vulnerability at different spatial and temporal scales using subjective assessments, rules of thumb and analytical and simulation models are reviewed. The application of information on vulnerability and persistence to conservation planning and management is discussed under the headings of natural dynamics, replication of protection, levels of representation, source and sink population structures, refuges and critical resources, reserve design, habitat fragmentation and levels of management.

Animals↗
PubMed2002

Physiological variation in insects: large-scale patterns and their implications.

In this paper we demonstrate how broad scale comparative physiology has an important role to play in informing a variety of assumptions made in macroecology. We do so by examining large-scale geographic variation in insect development, thermal tolerance and metabolic rate. From these studies, and those from the literature on insect water loss and thermoregulation, we show that there is often a bias to the geographic extent of available empirical data. Studies of cold hardiness are most usually undertaken at high latitudes, while investigations of upper thermal tolerances and water loss are most common in warm arid regions. Likewise, we demonstrate that much variation in insect physiological tolerances is partitioned at higher taxonomic levels, which has important implications for comparative physiology. Intriguingly, data on the full range of variables we review are available for only three species. We also show that, despite its importance, body size is regularly reported in only some kinds of investigations (metabolic rate, water loss rate), whereas in others (upper lethal temperature, cold hardiness, development) this variable is often ignored. In short, although large-scale comparative physiology can contribute considerable understanding to both physiology and ecology, there is much that remains to be done.

Animals↗
PubMed2001

The animal species-body size distribution of Marion Island.

Body size is one of the most significant features of animals. Not only is it correlated with many life history and ecological traits, but it also may influence the abundance of species within, and their membership of, assemblages. Understanding of the latter processes is frequently based on a comparison of model outcomes with the frequency of species of different body mass within natural assemblages. Consequently, the form of these frequency distributions has been much debated. Empirical data usually concern taxonomically delineated groups, such as classes or orders, whereas the processes ultimately apply to whole assemblages. Here, we report the most complete animal species-body size distribution to date for those free-living species breeding on sub-Antarctic Marion Island and using the terrestrial environment. Extending over 15 orders of magnitude of variation in body mass, this distribution is bimodal, with separate peaks for invertebrates and vertebrates. Under logarithmic transformation, the distribution for vertebrates is not significantly skewed, whereas that for invertebrates is right-skewed. Contrary to expectation based on a fractal or pseudofractal environmental structure, the decline in the richness of species at the smallest body sizes is a real effect and not a consequence of unrecorded species or of species introductions to the island. The scarcity of small species might well be a consequence of their large geographic ranges.

Animals↗
PubMed2000

Geographic range size and evolutionary age in birds.

Together with patterns of speciation and extinction, post-speciation transformations in the range sizes of individual species determine the form of contemporary species range-size distributions. However, the methodological problems associated with tracking the dynamics of a species' range size over evolutionary time have precluded direct study of such range-size transformations, although indirect evidence has led to several models being proposed describing the form that they might take. Here, we use independently derived molecular data to estimate ages of species in six monophyletic groups of birds, and examine the relationship between species age and global geographic range size. We present strong evidence that avian range sizes are not static over evolutionary time. In addition, it seems that, with the regular exception of certain taxa (for example island endemics and some threatened species), range-size transformations are non-random in birds. In general, range sizes appear to expand relatively rapidly post speciation; subsequently; and perhaps more gradually, they then decline as species age. We discuss these results with reference to the various models of range-size dynamics that have been proposed.

Animals↗
PubMed2000

Global patterns in biodiversity.

To a first approximation, the distribution of biodiversity across the Earth can be described in terms of a relatively small number of broad-scale spatial patterns. Although these patterns are increasingly well documented, understanding why they exist constitutes one of the most significant intellectual challenges to ecologists and biogeographers. Theory is, however, developing rapidly, improving in its internal consistency, and more readily subjected to empirical challenge.

Animals↗
PubMed2000

Using presence-absence data to establish reserve selection procedures that are robust to temporal species turnover.

Previous studies suggest that a network of nature reserves with maximum efficiency (obtained by selecting the minimum area such that each species is represented once) is likely to be insufficient to maintain species in the network over time. Here, we test the performance of three selection strategies which require presence-absence data, two of them previously proposed (multiple representations and selecting an increasing percentage of each species' range) and a novel one based on selecting the site where each species has exhibited a higher permanence rate in the past. Multiple representations appear to be a safer strategy than selecting a percentage of range because the former gives priority to rarer species while the latter favours the most widespread. The most effective strategy was the one based on the permanence rate, indicating that the robustness of reserve networks can be improved by adopting reserve selection procedures that integrate information about the relative value of sites. This strategy was also very efficient, suggesting that the investment made in the monitoring schemes may be compensated for by a lower cost in reserve acquisition.

Animals↗
PubMed2000

Thermal tolerance, climatic variability and latitude.

The greater latitudinal extents of occurrence of species towards higher latitudes has been attributed to the broadening of physiological tolerances with latitude as a result of increases in climatic variation. While there is some support for such patterns in climate, the physiological tolerances of species across large latitudinal gradients have seldom been assessed. Here we report findings for insects based on published upper and lower lethal temperature data. The upper thermal limits show little geographical variation. In contrast, the lower bounds of supercooling points and lower lethal temperatures do indeed decline with latitude. However, this is not the case for the upper bounds, leading to an increase in the variation in lower lethal limits with latitude. These results provide some support for the physiological tolerance assumption associated with Rapoport's rule, but highlight the need for coupled data on species tolerances and range size.

Adaptation, Physiological↗
PubMed2000

Robustness of reserve selection procedures under temporal species turnover.

Complementarity-based algorithms for the selection of reserve networks emphasize the need to represent biodiversity features efficiently, but this may not be sufficient to maintain those features in the long term. Here, we use data from the Common Birds Census in Britain as an exemplar data set to determine guidelines for the selection of reserve networks which are more robust to temporal turnover in features. The extinction patterns found over the 1981-1991 interval suggest that two such guidelines are to represent species in the best sites where they occur (higher local abundance) and to give priority to the rarer species. We tested five reserve selection strategies, one which finds the minimum representation set and others which incorporate the first or both guidelines proposed. Strategies were tested in terms of their efficiency (inversely related to the total area selected) and effectiveness (inversely related to the percentage of species lost) using data on eight pairs of ten-year intervals. The minimum set strategy was always the most efficient, but suffered higher species loss than the others, suggesting that there is a trade-off between efficiency and effectiveness. A desirable compromise can be achieved by embedding the concerns about the long-term maintenance of the biodiversity features of interest in the complementarity-based algorithms.

Algorithms↗
PubMed1994

Animal body size distributions change as more species are described.

Frequency distributions of body size have been reported in the literature for a range of animal higher taxa. However, the reported shapes of these distributions may be biased by species missing from them, specifically by currently undiscovered species. There is a body of evidence that the small-bodied species in a taxon are described later, on average, than the large-bodied. From this, we predict that the means of animal body size frequency distributions should decrease through time, and the skewnesses of the distributions increase. These predictions are shown to be true for body size distributions for five different higher taxa of animals. Thus, any reported body size distribution for a taxon is likely to be systematically biased, even if it includes all the species which are known, if many species are likely to remain undiscovered.

Animals↗