Abstract

Ecological phenomena operate at different spatial scales and are not uniform across landscapes or through time. One ecological theory that attempts to account for scaling and spatiotemporal variances is hierarchical patch dynamics. It introduces a hierarchical patch network with smaller spatiotemporal scales being nested within larger scales. However, few studies have modeled its presence within animal population dynamics. Locusts are an excellent model for investigating the spatiotemporal hierarchy of animal population dynamics, due to their high migratory capacity, large geographic ranges that extend across widely differing environments, and available long‐term data on distributions. Here, we investigated the influence of preceding vegetation growth on desert locust Schistocerca gregaria and Australian plague locust Chortoicetes terminifera outbreaks on three spatial levels (species range > geographic region > land unit) and between seasons. Both species are dryland herbivores with population dynamics linked to habitat productivity pulses after rain. We used NDVI data (MODIS imagery) as a measure of vegetation growth in hierarchical generalized additive models at different scales. Locust outbreaks were either preceded by vegetation growth between 78 and 32 days (Australian plague locusts) or 32 and 20 days before (desert locust) the observation. Although prior vegetation growth characterized outbreaks of both species, the temporal pattern of NDVI differed between spatiotemporal levels. All model selection criteria selected for a similar spatial hierarchy for both species: geographic region > land unit which supports the hierarchical patch dynamics paradigm. Further, it illuminates important timing differences between geographic regions and land units for preceding vegetation growth and locust outbreaks which can help locust managers identify when and where outbreaks occur. By acknowledging the spatiotemporal patterning of locust abundance, we account for heterogeneity of population dynamics throughout species ranges. Our findings demonstrate the importance of incorporating spatiotemporal variation in population models of insects and other animals.

Highlights

  • The spatiotemporal dynamics of populations has been a central theme in ecology for over a century (Grinnell 1917, Davidson and Andrewartha 1948, Andrewartha and Birch 1954, Macarthur 1958, Hanski 1998)

  • We investigate how changes in preceding vegetation growth predicts nymphal outbreaks of two locust species that occur on different continents using three, nested spatial levels and temporally through seasonality (Fig. 1)

  • Akaike information criterion (AIC), Bayesian information criterion (BIC), OOS deviance selected to include all levels: geographic zone, land unit and season while AUC selected for two models: all levels and geographic zone and land unit only models (Supporting information)

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Summary

Introduction

The spatiotemporal dynamics of populations has been a central theme in ecology for over a century (Grinnell 1917, Davidson and Andrewartha 1948, Andrewartha and Birch 1954, Macarthur 1958, Hanski 1998). There remains wide scope for investigating and understanding the abiotic (e.g. climate, geological variances) and biotic (e.g. food availability) factors affecting the dynamics of each species (Council 2001, Sutherland et al 2013, Padilla et al 2014, Stacey 2017). Caribou and elk populations are distributed by multi-scale resource selections: from individual and herd home ranges to the entire species range (Johnson 1980, Johnson et al 2004, Coe et al 2011, Decesare et al 2012). Since vegetation and animals are heterogeneously distributed because of spatiotemporal variation in climatic and other abiotic factors (Watt 1947, Greig-Smith 1979, Condit et al 2000, Ives et al 2008), a spatiotemporal hierarchy of animal population dynamics must be acknowledged

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