The pattern and range of movement of a checkered beetle predator relative to its bark beetle prey
ABSTRACT Theoretical studies of predator-prey population dynamics have increasingly centered on the role of space and the movement of organisms. Yet, empirical studies have been slow to follow suit. Herein, we quantified the long-range movement of a checkered beetle, Thanasimus dubius, which is an important predator of a pernicious forest pest, the southern pine beetle, Dendroctonus frontalis. Adult checkered beetles were marked and released at five sites and subsequently recaptured at traps baited with pine and pine beetle semiochemicals and located at distances up to 2 km away from the release point. While the pattern of recaptures-with-distance at each site provided a modest fit to a simple random-diffusion model, there was a consistent discrepancy between observed and expected recaptures: a higher than expected proportion of beetles were recaptured at the more distant traps. To account for this deviation, we developed a model of diffusion that allowed for simple heterogeneity in the population of marked beetles; i.e., a slow and fast moving form of the checkered beetle. This model provided a significantly better fit to the data and formed the basis for our estimates of intra-forest movement. We estimated that on average, one half of the checkered beetles dispersed at least 1.25 km, one third dispersed>2 km, and 5% dispersed>5 km. The source of the heterogeneous dispersal rates were partially due to differences in beetle size: smaller beetles (for both males and females) were more likely to be recaptured away from the release site than larger beetles. The southern pine beetle (prey for the checkered beetle) exhibited no significant heterogeneity in dispersal ability and provided a very good fit to the simple diffusion model. The only difference in dispersal between these two species was that checkered beetles were undergoing greater long-distance dispersal than the pine beetles (the radius containing 95% of the dispersing individuals was 5.1 km for the checkered beetle and 2.3 km for the pine beetle). Data on the movement of these two species is used to evaluate a general model of spatial pattern formation in a homogeneous environment, and the potential of the checkered beetle as a biological control agent for the southern pine beetle.
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ABSTRACT: Interactions among below- and above- ground processes are widely recognized as important yet poorly understood components of terrestrial ecosystem functioning. This lack of understanding rises in part from practical difficulties working with subterranean organisms, and also from biologically based differences in the relevant spatial and temporal scales of various species. This research will focus on one type of interaction, effects of root-colonizing insect-fungal complexes on above- ground herbivory. In particular, it will emphasize the subcortical guilds of conifer roots and stems. The root-colonizing guild of red pine includes six principal beetle species that partition the resource based on host histology, condition, and semiochemistry, and vector weakly phytopathogenic fungi. The stem-colonizing guild consists of two major bark beetle-fungal complexes, and several species of sapwood borers. The stem-, but not root- colonizers are strongly impacted by several species of habitat-specialist predators. Previous work from 1986-present includes field censuses of tree colonization & condition, excavation of selected stands, systematic isolation of fungi from roots, tree physiological & insect behavioral assays, and population sampling. Results lead to the proposed model: Root colonizing beetles enter and vector fungi into a few trees in new stands. These organisms do not kill mature trees, but compromise conductance between above- and below- ground tissues. This reduces trees' ability to resist lethal bark beetle attacks in the stem. Fungi spread through root grafts, exerting continued feedback to the above, and yielding a radial pattern of host mortality. Early succession plants colonize the expanding gaps, leading to faunistic changes. Several features of this interaction require further understanding before this model can be accepted: 1) High spatial autocorrelation allows for other relationships to be responsible; 2) Continual long-term data are limited to one of the 30 stands examined; 3) Observed physiological changes are consistent with the model, but pose the same limitations; 4) Stand manipulation lacks replication and detailed observations; 5) The presumption that colonization by stem insects is required for tree mortality is untested; 6) Statistical associations suggest an important role of predators, but there is strong multi-covariance. Resolution of these issues requires long term, multidisciplinary, and hypothesis-driven research, and hence is well suited for LTREB. The overall purpose of this research is to explore the role of one ecosystem process, herbivory, in interactions between below- and above- ground functions. Specific objectives are to 1) Evaluate the role of below-ground herbivory on susceptibility to above-ground herbivores, with particular emphasis on spatial / temporal patterns of colonization, physiological changes within trees, tree mortality & forest gaps, and vegetational changes; 2) Evaluate the degree of connectedness among forests harboring common below- and above- ground feeding guilds by measuring movement of root beetles, bark beetles, & predators; 3) Conduct manipulative experiments to test the relative importance of inciting agents, stem colonizing organisms, and predators in tree mortality and gap formation. The working hypotheses to be tested by long-term sampling and repeated assays are: a) Stem colonization is more likely in trees whose roots are previously colonized by root beetles & associated fungi; b) Spatial spread of mortality reflects a stereotypic sequence of root, stem phloem, and stem sapwood colonization; c) Colonization of root tissue compromises tree defenses against stem colonizers; d) Interactions among below- and above- ground processes contribute to gap formation and altered vegetational pathways; e) Predator - bark beetle - host
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ABSTRACT: In predator–prey interactions, a widely held view is that prey species have higher dispersal rates relative to their predators and are thereby able to escape from predation by colonizing habitats before their predators. Despite major implications for predator–prey interactions, community assembly, and biological control, this view has rarely been tested, and measuring relative dispersal abilities is often complicated by colonizing predators and prey originating from different locations. In California’s San Joaquin Valley, the periodic harvest of alfalfa presents an opportunity to measure dispersal of a key generalist pest, Lygus spp., relative to a suite of its generalist predators. We performed a large-scale mark-capture study by marking a mature alfalfa field containing Lygus and its predators with an aerial application of a protein marker. The alfalfa was then harvested by the grower, prompting a dispersal event. At several times following harvest, surrounding cotton fields were sampled at known distances from the marked field to quantify movement by Lygus and its predators. Contrary to the general view, our data do not suggest that Lygus routinely out-disperses its suite of predators. Instead, the mean dispersal distance for Lygus fell near the average dispersal distances of its predators. Implications for biological control are discussed in light of these results, and the importance of predators’ trophic strategy is stressed.Biological Control 12/2012; 63(3):296–303. · 1.87 Impact Factor
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ABSTRACT: Abstract. 1. Dispersal patterns of a beetle inhabiting tree hollows, Osmoderma eremita (Scopoli, 1763) (Coleoptera: Cetoniidae), were studied in a cork oak (Quercus suber) woodland in central Italy, the southernmost part of its distribution range. During 2 years, we used radio telemetry to monitor dispersal of 39 free-ranging individuals (16 males, 23 females). 2. Telemetered beetles spent their lifetime not only inside hollow trees but also in other habitats, such as above or under the ground surface. 3. Beetles were more active at the beginning of the season. Eighty-one per cent of the males and 69% of the females conducted dispersals during their lifetime. 4. The dispersal distance over individuals’ lifetime did not differ between sexes. The longest dispersal was conducted by a female that moved 1504 m. Thirty-nine per cent of dispersing individuals reached distances farther than 250 m. Both dispersal rate and range are higher than what has been found in Northern Europe. 5. The population size per tree is low, most of the adults leave their natal tree, and a high predation rate (at least 28%) was observed among dispersing beetles. Therefore, to balance the local extinction risk from single trees, a high density of hollow trees is probably required. It is desirable that suitable trees are concentrated at a spatial scale of a few hundred metres.Insect Conservation and Diversity 05/2013; 6:309-318. · 1.94 Impact Factor