Density‐dependent habitat selection and the ideal free distribution in marine fish spatial dynamics: considerations and cautions

Abstract

Introduction 142Abundance-area relationships 142Habitat specific -total population growth relationship 144Commonality in spatial dynamic models 145Does density-dependent habitat selection exist in marine fish? 148Effect of spatial scale 149 Conclusion 150Acknowledgements 150References 151Abstract Current methods and theory used in the study of the spatial dynamics of marine fish are problematic. Positive relationships between population abundance and occupied area are typically interpreted as evidence of density-dependent habitat selection. However, both abundance and area may co-vary with an un-parameterized variable, such as a density-independent effect. In addition, if density-dependent habitat selection is present, population growth rates in optimal habitats would be expected to be lower than in marginal habitats. This same pattern can also evolve from a largescale, spatially autocorrelated change in a density-independent factor. The theory underlying density-dependent habitat selection, the ideal free distribution, can be tautological when no a priori information of how habitat suitability changes with density is known. In this case, an ideal free distribution can be defined for any pattern of habitat-specific population growth rates. However, these problems are not insurmountable and solutions may be found by considering spatial variation in proxies of fitness and explicitly allowing for the relative importance of habitat selection (density dependent) and environmental (density independent) effects to vary with spatial scale.

Does Slow and Variable Recovery of Diadema antillarum on Caribbean Fore-Reefs Reflect Density-Dependent Habitat Selection?

“…We propose that the D. antillarum distribution patterns observed in this study, when combined with temporal data ( Van der Hal, 2005;Debrot and Nagelkerken, 2006), and observed differences in ecosystem characteristics between habitat types, are in line with expectations from the theory of density-dependent habitat selection (see Fretwell and Lucas, 1969;Fretwell, 1972;Morris, 1989;Shepherd and Litvak, 2004). Our data elucidate potential mechanisms by which sheltered, lagoon, and backreef habitats confer higher levels of fitness on D. antillarum than forereefs.…”

Non-additive and non-stationary properties in the spatial distribution of a large marine fish population

“…Often however, changes in population abundance (and occupancy) can co-occur with large-scale changes in environmental variables, such as water temperature [10]. In such circumstances, it becomes harder to disentangle the multiple influences on species occupancy, or the degree to which a change in temperature may facilitate or curtail a change in occupancy [11,12]. We contend that densitydependent and density-independent sources of variability affect population spatial distribution in a non-additive fashion, a prediction that we refer to as the non-additive species -environment hypothesis.…”

“…Turner [15] also points out that species distribution can undergo strong nonlinearities that result in drastic changes in spatial configurations in relation to small changes in forcing variables. Within these contexts, it is crucial to investigate the underlying mechanisms that control species occupancy [11,16], and specifically, whether there are threshold values of population abundance that once crossed can cause drastic changes in the geographical distribution of species. In keeping with Gaston et al [14], we expect that during periods in which population abundance is relatively constant species occupancy is mostly responsive to density-independent variables.…”

Evaluating the effect of fishery closures: Lessons learnt from the Plaice Box

“…Negative feed-back processes to consider are density-dependent effects in growth rate (Lorenzen and Enberg, 2002), natural mortality (Modin and Pihl, 1994), and changes in distributions (Shepherd and Litvak, 2004). Another negative feed-back process is the response of plaice to trawling disturbance ).…”