Spatially explicit analyses unveil density dependence

Abstract

Density-dependent processes are fundamental in the understanding of species population dynamics. Whereas the benefits of considering the spatial dimension in population biology are widely acknowledged, the implications of doing so for the statistical detection of spatial density dependence have not been examined. The outcome of traditional tests may therefore differ from those that include ecologically relevant locational information on both the prey species and natural enemy. Here, we explicitly incorporate spatial information on individual counts when testing for density dependence between an insect herbivore and its parasitoids. The spatially explicit approach used identified significant density dependence more frequently and in different instances than traditional methods. The form of density dependence detected also differed between methods. These results demonstrate that the explicit consideration of patch location in density-dependence analyses is likely to significantly alter current understanding of the prevalence and form of spatial density dependence in natural populations.

Relationship between rust mitesCalepitrimerus vitis(Nalepa), bud mitesColomerus vitis(Pagenstecher) (Acari: Eriophyidae) and short shootsyndrome in Oregon vineyards

“…The remainder of the blocks had too few vines with mites and SSS and did not meet these requirements and were therefore not used in this analysis. In all cases, only values of v i larger than 1.5 (significant patches) and values of v j smaller than -1.5 (significant gaps) (Perry and Dixon, 2002) and values of X k > 0.5 (significant association) or < -0.5 (significant disassociation) (Veldtman and McGeoch, 2004) were used to create the spatial maps. Rust mite incidence and SSS had a spatially aggregated pattern in block 1 at Dundee (Table 4).…”

Can inverse density dependence at small spatial scales produce dynamic instability in animal populations?

“…Consequently, predation could produce IDD mortality at the aggregation scale (due to numerical dilution of predator attacks among group members) but DDD mortality at the larger scale of predator foraging (due to predator aggregative and functional responses; White et al 2010). This phenomenon is probably not limited to reef fishes, and similar transitions between IDD and DDD across spatial scales have been observed in insect predator-prey interactions (Mohd Norowi et al 2000;Veldtman and McGeoch 2004). This type of scale-dependent transition between IDD and DDD mortality may also occur due to nonpredatory mechanisms, such as the transition from small-scale facilitation to large-scale competition for zooplankton prey in softsediment mussel beds (Gascoigne et al 2005).…”

“…Moreover, there is growing evidence that processes observed at different spatial scales in the same system may have opposing effects on population dynamics, such as inverse density dependence at one scale and direct density dependence at another (Mohd Electronic supplementary material The online version of this article (doi:10.1007/s12080-010-0083-z) contains supplementary material, which is available to authorized users. Norowi et al 2000;Veldtman and McGeoch 2004;White and Warner 2007).…”

Scale-dependent mechanisms in the population dynamics of an insect herbivore

“…Therefore, the adoption of a spatial perspective in population ecology has resulted in significant advances in the field, and also in the generation of novel hypotheses (e.g. Thomson et al 1996;Logerwell et al 1998;Hanski 1999;Stoll and Prati 2001;Brewer and Gaston 2003;Veldtman and McGeoch 2004).…”