Landscape mosaic induces traveling waves of insect outbreaks

Abstract

The effect of landscape mosaic on recurrent traveling waves in spatial population dynamics was studied via simulation modeling across a theoretical landscape with varying levels of connectivity. Phase angle analysis was used to identify locations of wave epicenters on patchy landscapes. Simulations of a tri-trophic model of the larch budmoth (Zeiraphera diniana) with cyclic population dynamics on landscapes with a single focus of high-density habitat produced traveling waves generally radiating outwardly from single and multiple foci and spreading to isolated habitats. We have proposed two hypotheses for this result: (1) immigration subsidies inflate population growth rates in the high connectivity habitat and, thus, reduce the time from valleys to peaks in population cycles; (2) populations in the high connectivity habitat crash from peaks to valleys faster than in an isolated habitat due to over-compensatory density dependence. While population growth rates in the high connectivity habitat benefitted from immigration subsidies, times from population valleys to peaks were greater in high connectivity habitat due to a greater magnitude of fluctuations. Conversely, the mean time of the crash from population peaks to valleys was shorter in high connectivity habitat, supporting the second hypothesis. Results of this study suggest over-compensatory density dependence as an underlying mechanism for recurrent traveling waves originating in high connectivity habitats aggregated around a single focus.

Periodic travelling waves in cyclic populations: field studies and reaction–diffusion models

“…Simple models of the form (3.1a) and (3.1b) also neglect the spatial heterogeneities that are a feature of all ecological habitats. For single (scalar) reaction-diffusion equations, there is now an established body of literature on the propagation of wavefronts in heterogeneous environments (reviewed comprehensively by Xin (2000) Johnson et al (2004Johnson et al ( , 2006 demonstrated periodic travelling waves originating in regions with a high density of habitat patches aggregated around a single focus; the waves travel towards the surrounding and more isolated habitat patches. The natural analogue of this for reaction-diffusion models would be periodic travelling wave generation by spatial gradients in parameter values; to the best of our knowledge, this has not been investigated.…”

“…Note that not all populations of the selected taxa are cyclic. taxon cycle period examples of interactions hypothesized to be generating the cycles spatial dynamics (TWZtravelling waves) possible hypothesis for spatial dynamics larch budmoth, Zeiraphera diniana 8-10 years (Turchin 2003) plant-moth-parasitoid (Turchin 2003), plant-herbivore (Selås 2006a) TW (Bjørnstad et al 2002;Johnson et al 2004) gradients in habitat connectivity and site productivity (Johnson et al 2004(Johnson et al , 2006) southern pine beetle, Dendroctonus frontalis 6-9 years (Turchin 2003) predator-prey (Turchin 2003;Turchin et al 1999), plant-herbivore (Selås 2006a) isolated patchy outbreaks (Turchin et al 1998;Okland et al 2005) diffusion-driven instability by predator -prey interaction (Turchin et al 1998) red grouse, Lagopus lagopus scoticus 6-11 years (Turchin 2003) parasite-grouse (Hudson et al 1998;Lambin et al 1999;Turchin 2003;Redpath et al 2006), kin selection (Moss et al 1996;Matthiopoulos et al 2003Matthiopoulos et al , 2005Turchin 2003;Mougeot et al 2005), plant-herbivore (Selås 2006a) regional synchrony in some years (Cattadori et al 2005), TW (Mougeot et al 2005) seasonal forcing (Cattadori et al 2005), habitat boundary , productivity gradient (Johnson et al 2006) Fennoscandian voles, Microtus spp. and Clethrionomys spp.…”

Spatial Dispersal of Douglas-Fir Beetle Populations in Colorado and Wyoming

“…Directional anisotropies in dispersal patterns would likely be the result of wind patterns and stand structure [26], among other factors requiring subsequent analysis. Of additional consideration here would be the relationship of dispersal to differences in habitat connectivity or the ability to traverse landscape topography [30] and related aspects of habitat connectivity and fragmentation [31]. Coulson and Witter [32] divided the process of dispersal into two categories, active and passive, with active dispersal taking the form of flying or walking and passive dispersal involving windborne transport.…”

Generation of periodic travelling waves in cyclic populations by hostile boundaries

“…Other examples include PTWs and patterns of regional synchrony in geometrid moths in Northern Fennoscandia [5][6][7][8][9], PTWs and intermittent synchrony in red grouse [10,11], and PTWs in larch budmoth in the European Alps [12][13][14]; see Sherratt & Smith [15] for further examples. Modelling studies have demonstrated a number of potential causes for this spatial asynchrony, including invasions [16][17][18][19][20][21], heterogeneous habitats [13,[22][23][24], migration between subpopulations [25], migration driven by pursuit and evasion [26] and hostile habitat boundaries [27][28][29][30]. This paper concerns the last of these.…”