Dispersal and edge behaviour of bark beetles and predators inhabiting red pine plantations

Abstract

1 Quantifying dispersal in predator-prey systems can improve our understanding of how these species interact in space and time, as well as their relative distributions across complex landscapes. 2 We measured the dispersal abilities of three forest insects associated with red pine decline: the eastern five spined pine engraver Ips grandicollis (Coleoptera: Curculionidae), its main predator Thanasimus dubius (Coleoptera: Cleridae) and the basal stem and root colonizer Dendroctonus valens (Coleoptera: Curculionidae). We also examined the edge behaviours of these species and the predator Platysoma spp (Coleoptera: Histeridae) between red pine stands (habitat) and clearings (nonhabitat). 3 Thanasimus dubius dispersed 12 times farther than its prey I. grandicollis, with 50% of predators dispersing farther than 1.54 km. This profound difference in dispersal behaviour between prey and predator may contribute to the clumped distribution of I. grandicollis. 4 Most T. dubius and D. valens were confined in the pine forest, thus showing strong edge behaviour. This differed from I. grandicollis and Platysoma spp., which were commonly found in open areas adjacent to red pine plantations. 5 The bark beetle I. grandicollis and one of its main predators, T. dubius, exhibited different patterns of movement within a fragmented landscape. Despite a greater dispersal ability of T. dubius within forests, the spatial distribution of this predator may be restricted by fragmentation of its habitat, and provide an opportunity for partial escape of its prey. 6 The present study contributes to our knowledge of top-down forces within red pine stands undergoing decline. Differences of dispersal patterns and edge behaviour could contribute to the initiation of new pockets of decline, as well as the connectedness among existing ones.

Species diversity and predation strategies in a multiple species predator–prey model

“…The peak position of predator survival has shifted to a lower value of c max and the survival rate has increased slightly in comparison to (12), in a similar way to how the peak position and survival rate in (11) shifted in comparison to (3). As shown in in table 4 the peak position of predator survival is occurring at c max = 5.9 and r max = 3.2, with a predator survival rate of 0.304 and prey survival rate of 0.75.…”

“…, Thus for the strategies defined by (3), (12) and (14) the point of peak predator diversity in the co-survival space is very close to the edge of total collapse, with c max only having to increase slightly for no predators to survive. Strategies (11), (13) and (15) all contain smarter predators, which redistribute their effort in the event of a prey becoming extinct, all three of these predation strategies exhibit similar changes to the region of co-survival when compared the predation strategies that do not dynamically redistribute the predators efforts, with a large region of supressed predator survival and a fixed value of c max for which predator survival first occurs arising.…”

“…(3), this will increase the amount of effort in predating on prey with the largest c ij value but decrease the value for the smallest c ij values As with the original predation strategy (3), (12) does not vary with time. However, the combination of (11) and (12), in which the predators both focuses their efforts and are aware that a prey has become extinct can be formulated as:…”

“…However, the combination of (11) and (12), in which the predators both focuses their efforts and are aware that a prey has become extinct can be formulated as:…”

“…Survival rates for a a n=m=100 ecosystem with the use of the predation strategy outlined in (12) This figure shows survival rates after 100 runs of the model and 5000 time steps at each run for n = 100 m = 100 using the predation strategy outlined in (7). A greyscale color bar is provided to identify the rate of survival at each point..…”