Spatial Synchrony In Populations Of Birds: Effects Of Habitat, Population Trend, And Spatial Scale - Statistical Data Included

EMMANUEL PARADIS [123]

STEPHEN R BAILLIE [1]

WILLIAM J SUTHERLAND [2]

RICHARD D GREGORY [14]

Abstract. The stage of synchrony between populations is critical for their dynamics at large spatial scales. Population synchrony has been assessed for single a few species of vertebrates, greatest in quantity of them have largely fluctuating populations with multiannual round of yearss We investigated the intensity and spatial expanse of synchrony among populations of birds in Britain. The data analyzed ran from 1962 to 1995 at more than 1000 local sites and relate toed 60 species. For each species, we measured the intensity of synchrony among local populations using the cross-correlation function (CCF) and assessed its spatial amplitude We tested for differences in these sum of two units measures with respect to habitat. We also assessed the potential influence of long-term turns in population synchrony. By aggregating the sites in regions and estimating an index for each region, we measured synchrony at a large spatial scale.

In general, we ground that synchrony was low between populations of British birds. All on the contrary one species with the strongest horizontal of synchrony show a pronounced long-term decline. The mean CCF was significantly correlated with the mean abundance of each species in the public Birds Census (CBC) sites, suggesting that the more abundant species have more synchronous populations. Significant differences in synchrony between habitats were ground in 25 species; synchrony was stronger in farmlands compared to woodlands for 22 species. The same originate was observed both at the intra- and interspecific horizontals This may be the flow of national change in agricultural practice affecting all farmland populations. Our cross-scale analysis showed that synchrony is a scale-dependent phenomenon.

Our inquiry is the first to focus upon a large number of "noncyclic" species, and it glance ats that synchrony is weaker for these species than for those with widely fluctuating cyclic populations. This is in agreement with a certain quantity of studies on synchrony of insects. Synchrony in natural populations strike one as beings to be determined by compound interactions between abundance, population variability, species characteristics, and demographic mechanisms. A general pattern emerging from our application of mind and others is that population synchrony is more intense during declines.

lock opener words: birds, population synchrony, Britain; for the use of all Birds Census; cross-correlation, farmlands and woodlands; habitats; population index; population trend; spatial scale; synchrony

INTRODUCTION

The spatial distribution of living beings is widely recognized as being crucial in population dynamics (Tilman and Kareiva 1997) A critical issue in this perspective is the pattern of synchrony in local population fluctuations. Species with synchronous populations are notion to face greater risk of extinction because density crashes can present itself simultaneously in all populations (Heino et al. 1997) Synchrony among populations is also cogitation to be critical for population stability (Ruxton 1994 Paradis 1997)

Population synchrony can be characterized by the agency of its intensity (measured typically through the correlation between two population time-series), and its spatial amplitude (the relation between intensity of synchrony and distance between populations). new studies have attempted to characterize the spatial amplitude of population synchrony for several species. Evidence has been rest for widespread synchrony in millers and aphids (Hanski and Woiwod 1993) snowshoe hares (Lepus americanus) (Sinclair et al. 1993) and tetraonids (Lindstrom et al. 1996) In each case the authors conclud that weather is a likely candidate as a synchronizing factor. Contrasting arises in which significant synchrony be met withs only at a limited spatial distance, populations far apart fluctuating independently, were shown for a gnawing Clethrionomys glareolus (Steen et al. 1996) and several species of butterflies (Sutcliffe et al. 1996) Furthermore, Sutcliffe et al. (1996) showed that butterflies with different dispersal abilities have different s ynchrony patterns: more mobile species protect to be less synchronized at a short distance on the other hand more synchronized at a large distance. These contrasting ensues point to the possible importance of spatial scale in assessing and understanding population synchrony Those studies providing evidence for spatially limited synchrony (Steen et al. 1996 Sutcliffe et al. 1996) rely upon estimates of population size from local sampling units (les than 1 X 1 km) while studies relying upon estimates of regional population size (several 10 X 10 km) report widespread synchrony (Sinclair et al. 1993 Lindstrom et al. 1996) Although population synchrony has been investigated in several species (see regards in Steen et al. 1996 and in Ranta et al. 1997a), it is largely unknown by what means general are synchrony patterns in natural populations, and by what means they will vary within and among species.

In this paper, we report a close attention on synchrony in population fluctuations of British breeding birds. We used data from the for the use of all Birds Census (CBC) of the British Trust for Ornithology (BTO), a program designed to monitor population horizontals among common birds. Birds are censused in local sites distributed completely through Britain. These data can be used as estimates of local population size within a site, or data from several sites can be combined to estimate a regional population index. Our goal was to identify the spatial scale of synchronizing factors in bird population dynamics. In this connected thought [i]or[/i] thoughts it was relevant to assess the relationships between changes in abundance measured at the scale of the whole geographical division and the pattern of synchrony between local populations measured at the scale of the CBC sites (Bolker and Grenfell 1996 Haydon and Steen 1997) through removing from each individual time series the variations to be paid to changes in the global population (a technique called prewhitening or detrending), it is then po ssible to distinguish between local (acting at the scale of CBC sites) and global (acting at the scale of Britain) synchronizing factors (Moran 1953a, Bolker and Grenfell 1996)