Non-invasive genetic monitoring for the threatened valley elderberry longhorn beetle.

The valley elderberry longhorn beetle (VELB), Desmocerus californicus dimorphus (Coleoptera: Cerambycidae), is a federally threatened subspecies endemic to the Central Valley of California. The VELB range partially overlaps with that of its morphologically similar sister taxon, the California elderberry longhorn beetle (CELB), Desmocerus californicus californicus (Coleoptera: Cerambycidae). Current surveying methods are limited to visual identification of larval exit holes in the VELB/CELB host plant, elderberry (Sambucus spp.), into which larvae bore and excavate feeding galleries. Unbiased genetic approaches could provide a much-needed complementary approach that has more precision than relying on visual inspection of exit holes. In this study we developed a DNA sequencing-based method for indirect detection of VELB/CELB from frass (insect fecal matter), which can be easily and non-invasively collected from exit holes. Frass samples were collected from 37 locations and the 12S and 16S mitochondrial genes were partially sequenced using nested PCR amplification. Three frass-derived sequences showed 100% sequence identity to VELB/CELB barcode references from museum specimens sequenced for this study. Database queries of frass-derived sequences also revealed high similarity to common occupants of old VELB feeding galleries, including earwigs, flies, and other beetles. Overall, this non-invasive approach is a first step towards a genetic assay that could augment existing VELB monitoring and accurately discriminate between VELB, CELB, and other insects. Furthermore, a phylogenetic analysis of 12S and 16S data from museum specimens revealed evidence for the existence of a previously unrecognized, genetically distinct CELB subpopulation in southern California

Evaluating the Long-Term Metacommunity Dynamics of Tree Hole Mosquitoes

Four different conceptual models of metacommunities have been proposed, termed “patch dynamics,” “species sorting,” “mass effect,” and “neutral.” These models simplify thinking about metacommunities and improve our understanding of the role of spatial dynamics both in structuring communities and in determining local and regional diversity. We tested whether mosquito communities inhabiting water-filled tree holes in southeastern Florida, USA, displayed any of the characteristics and dynamics predicted by the four models. The densities of the five most common species in 3–8 tree holes were monitored every two weeks during 1978–2003. We tested relationships between habitat variables and species densities, spatial synchrony, the presence of life history trade-offs, and species turnover. Dynamics showed strong elements of species sorting, but with considerable turnover, as predicted by the patch dynamics model. Consistent with patch dynamics, there was substantial asynchrony in dynamics for different tree holes, substantial species turnover in space and time, and an occupancy/colonization trade-off. Substantial correlations of density and occupancy with tree hole volume were consistent with the species-sorting model, but unlike this model, species did not have permanent refuges. No evidence of mass effects was found, and correlations between habitat variables and dynamics were inconsistent with neutral models. Our results did not match a single model and therefore caution against overly simplifying metacommunity dynamics by using one dynamical characteristic to select a particular metacommunity perspective

The Importance of Host Plant Limitation for Caterpillars of an Arctiid Moth (Platyprepia Virginalis) Varies Spatially

Spatial dynamic theories such as source–sink models frequently describe habitat-specific demographies, yet there are surprisingly few field studies that have examined how and why interacting species vary in their dynamics across multiple habitat types. We studied the spatial pattern of interaction between a chewing herbivore and its primary larval host plant in two habitat types. We found that the interaction between an arctiid caterpillar (Platyprepia virginalis) and its host (Lupinus arboreus) differed in wet vs. upland dry habitats, as did yearly population dynamics for the caterpillar. In upland sites, there was a strong positive relationship between lupine cover and the abundance of caterpillars although this relationship was not apparent in wet sites. Additionally, in wet sites, caterpillar populations were larger and less variable across years. Caterpillars appeared to exhibit source–sink dynamics, with the time-averaged finite growth rate λ \u3e 1 in wet sites (sources), λ \u3c 1 in upland dry sites (sinks), and predominant source-to-sink movement of late-instar caterpillars. Populations in upland dry sites also went locally extinct in years of low regional abundance. Emigration from wet sites could potentially explain the lack of coupling of herbivore and host plant dynamics in these sites. These results indicate that movement and other factors affecting demography are habitat-specific and have important implications for trophic control. Acknowledging such complexity makes simple models of trophic control seem overly general but may allow us to formulate more broadly applicable ecological models

Metapopulation Dynamics on Ephemeral Patches

A challenge for conservation management is to understand how population and habitat dynamics interact to affect species persistence. In real landscapes, timing and duration of disturbances can vary, and species' responses to habitat changes will depend on how timing of dispersal and reproduction events relate to the landscape temporal structure. For instance, increasing disturbance frequency may promote extinction of species that are unable to appropriately time their reproduction in an ever-changing habitat and favor species that are able to track habitat changes. We developed a mathematical model to compare the effects of pulsed dispersal, initiated by shifts in habitat quality, with temporally continuous dispersal. We tested the effects of habitat (and population) turnover rates on metapopulation establishment, persistence, and long-term patch occupancy. Pulsed dispersal reduced patch occupancy and metapopulation longevity when habitat patches are relatively permanent. In such cases, demographic extinction was the primary form of local extinction. Conversely, when habitat patches are short-lived and new ones are frequently formed, pulsed dispersal promoted rapid colonization, increased occupancy, and prolonged metapopulation persistence. Our results show that species responsiveness to habitat disturbance is critical to metapopulation persistence, having profound implications for the species likely to persist in landscapes with altered disturbance regimes

Rethinking a rare-species conservation strategy in an urban landscape: the case of the valley elderberry longhorn beetle

Reflecting the lack of critical information for most protected species, recovery plans for organisms listed as threatened or endangered under the U.S. Endangered Species Act tend to oversimplify habitat descriptions. Here we present our approach for improving the definition of habitat for rare and patchily distributed listed species. The valley elderberry longhorn beetle (Desmocerus californicus dimorphus) occurs in riparian and scrub communities in California's Central Valley. Habitat quality for the species currently is defined essentially exclusively in terms of presence and abundance of its larval host plant, elderberry (Sambucus spp.). Using detailed measures of physical and biological attributes at diverse sites occupied by the beetle, we characterized and defined habitat quality on the basis of not only host plants, but on an array of biotic and abiotic environmental characteristics. We identified four geomorphically distinct habitat associations: alluvial plain, narrow riparian corridor, upper riparian plain, and non-riparian scrub. Depending on habitat type, the environmental characteristics most strongly associated with beetle presence were host plant availability, topography and proximity to habitat edge. Increased local population size of beetles was associated with higher elderberry density and the presence of larger, more mature plants. Stochasticity in site occupancy over space and time confounds our ability to identify sites that are most able to contribute to long-term beetle survival, while underscoring the importance of unoccupied habitat to the beetle. Adopting a multivariate definition of habitat may facilitate more effective identification of locations critical to the recovery of the valley elderberry longhorn beetle, and prioritization of those management actions that can contribute effectively to meeting conservation goals for the species

Data from: Habitat patch arrangement and metapopulation persistence of predators and prey

This study tests whether spatial dynamics can stabilize metapopulations with a small number of patches and tests the influence of patch arrangement. I measured persistence of predator and prey protists in replicated microcosms with two to four patches. Predators persisted for 85–437 generations (26–130 d). As predicted by single-species and/or predator-prey metapopulation models, substantial variation in predator metapopulation persistence was accounted for by the amount of patches or habitat, number of dispersal corridors, maximum interpatch distance, and proportion of patches providing colonists (which depends on the explicit spatial arrangement of patches). Contrary to expectation, persistence was not influenced by loops of patches or patch similarity. Persistence was also shorter in four-patch loops than three-patch loops, indicating an interaction between patch number and arrangement, which is not predicted by published models. Spatial synchrony of density fluctuations was central to predator persistence but had complex effects on extinction-colonization dynamics, rescue effects, and predator-prey interaction strength. Levins’s model, containing only extinction-colonization dynamics, predicted patch occupancy for prey but not predators. Predators did, however, show rescue effects and changes in interaction strength. This work illustrates the need to combine experimentation with modeling to understand the mechanisms of spatial dynamics