Large scale PVA modelling of insects in cultivated grasslands: the role of dispersal in mitigating the effects of management schedules under climate change

In many species, dispersal is decisive for survival in a changing climate. Simulation models for population dynamics under climate change thus need to account for this factor. Moreover, large numbers of species inhabiting agricultural landscapes are subject to disturbances induced by human land use. We included dispersal in the HiLEG model that we previously developed to study the interaction between climate change and agricultural land use in single populations. Here, the model was parameterized for the large marsh grasshopper (LMG) in cultivated grasslands of North Germany to analyze (1) the species development and dispersal success depending on severity of climate change in sub regions, (2) the additional effect of grassland cover on dispersal success, and (3) the role of dispersal in compensating for detrimental grassland mowing. Our model simulated population dynamics in 60-year periods (2020-2079) on a fine temporal (daily) and high spatial (250 x 250 m2) scale in 107 sub regions, altogether encompassing a range of different grassland cover, climate change projections and mowing schedules. We show that climate change alone would allow the LMG to thrive and expand, while grassland cover played a minor role. Some mowing schedules that were harmful to the LMG nevertheless allowed the species to moderately expand its range. Especially under minor climate change, in many sub regions dispersal allowed for mowing early in the year, which is economically beneficial for farmers. More severe climate change could facilitate LMG expansion to uninhabited regions, but would require suitable mowing schedules along the path. These insights can be transferred to other species, given that the LMG is considered a representative of grassland communities. For more specific predictions on the dynamics of other species affected by climate change and land use, the publicly available HiLEG model can be easily adapted to the characteristics of their life cycle.

Hitchhiking or hang gliding? Dispersal strategies of two cereal-feeding eriophyoid mite species

Dispersal shapes the dynamics of populations, their genetic structure and species distribution; therefore, knowledge of an organisms’ dispersal abilities is crucial, especially in economically important and invasive species. In this study, we investigated dispersal strategies of two phytophagous eriophyoid mite species: Aceria tosichella (wheat curl mite, WCM) and Abacarus hystrix (cereal rust mite, CRM). Both species are obligatory plant parasites that infest cereals and are of economic significance. We investigated their dispersal success using different dispersal agents: wind and vectors. We hypothesised that in both mite species the main mode of dispersal is moving via wind, whereas phoretic dispersal is rather accidental, as the majority of eriophyoid mite species do not possess clear morphological or behavioural adaptations for phoresy. Results confirmed our predictions that both species dispersed mainly with wind currents. Additionally, WCM was found to have a higher dispersal success than CRM. Thus, this study contributes to our understanding of the high invasive potential of WCM.

An experimental test of the capacity for long-distance dispersal of freshwater diatoms adhering to waterfowl plumage

Waterfowl are potential long-distance dispersal vectors for aquatic microbes such as diatoms, but experimental evidence is scarce. We conducted an experiment designed to emulate diatom dispersal via adherence to waterfowl, and to evaluate the effects of humidity and transport duration on potential dispersal success. We dipped individual mallard breast feathers in a pure benthic diatom culture (Nitzschia pusilla Grunow), then subjected them to one of four relative humidity levels (RH; from ca. 8% to 88%) crossed with one of four transport durations (10, 60, 120, 240 minutes) within a chamber through which air was passed continuously, mimicking light wind. We then placed the feather on sterile growth medium. After two weeks we used spectrofluorometry to detect diatom growth and thus diatom viability. A logistic regression on viability revealed a significant interaction between transport duration and RH: the negative effect of duration was strongest under lower RH conditions, but under high RH (88%) the probability of being viable was moderate to high regardless of transport duration. Importantly, even after 4 hours, the probability of being viable was predicted to be 0.45 (95% confidence interval: 0.18 to 0.75). We then placed our findings in the geographic context of the central waterfowl migration flyway in North America, and specifically Nebraska, South Dakota, and North Dakota, for which sufficient data were available to enable geospatial predictions of potential mallard-borne diatom dispersal. Combined with published data about (i) mallard flight speeds, (ii) the geographic distribution of surface waters and of N. pusilla, and (iii) daytime RH during the months of April through June, our model predicted high probabilities of potential dispersal among the region’s suitable water bodies.

Life-history traits matter for dispersal into semi-open habitat corridors:

Biodiversity face ever-increasing threats from the consequences of various human activities Conservation corridors have long been considered a viable solution to help counteract biodiversity loss. However, corridors simultaneously increase fragmentation for non-target habitats. To overcome this challenge, semi-open habitats, which are a mixture of open and woodland habitats, have been proposed as they may enable simultaneous dispersal of both stenotopic open and woodland species. Despite the fact that they could be used by a great range of species, strong interspecific variability exists with regards to the number of individuals effectively recorded in such environment. Consequently, generalisation about their effectiveness remains difficult. Life-history traits such as body size, hibernation stage, trophic guild, and habitat specialisation could be successfully used to enhance prediction with regards to dispersal success. We used generalized linear modelling to study the relationship of ground beetles species traits and dispersal success into semi-open habitat in two regions of Germany. Our preliminary results indicate that larger species, as well as species overwintering as larvae, tend to be more successful when dispersing into semi-open habitat than smaller species or species overwintering as adult. In addition, species locally abundant are also recorded in higher number. In the light of these results, semi-open corridors do not appear to be the best strategy to increase connectivity for species with small body size or overwintering as adult. For such species, priority should be given to traditional corridors whenever possible. Source habitats need also attention as population size will strongly determine the usefulness of such corridors.

Drivers of individual oak tree selection by acorn dispersing animals inferred from a genotyped seedling cohort

ABSTRACTSeed-dispersing animals can strongly influence plant reproductive success and resulting population structures. Few studies have disentangled different drivers of disperser foraging behavior in natural settings and their actual relevance for plant fitness. Here we adopt a novel approach to investigate the drivers of individual trees’ dispersal success in a mixed Pedunculate oak-Pyrenean oak (Quercus robur and Q. pyrenaica) forest stand. We genotyped a seedling cohort (n = 825) upon emergence and performed Bayesian parentage analyses to infer the acorn dispersal success of each oak tree in the stand. We then modeled this estimate as a function of six tree characteristics. The absolute number of animal-dispersed seedlings was exclusively predicted by crop size and the proportion of dispersed seedlings by the number of fruiting oaks in the neighborhood. Neither the oak species nor tree height, acorn size or shape played any role. Our findings contrast with results from experimental studies and suggest that effective acorn dispersers, despite being scatter-hoarders, behaved much like avian dispersers of fleshy-fruited species when selecting trees to forage on. Their behavior should favor the dominance of large, prolific trees for the dynamics and genetic composition of naturally regenerating oak stands.

Effects of mis-alignment between dispersal traits and landscape structure on dispersal success in fragmented landscapes

Dispersal is fundamental to population dynamics and hence extinction risk. The dispersal success of animals depends on the biophysical structure of their environments and their biological traits; however, comparatively little is known about how evolutionary trade-offs among suites of biological traits affect dispersal potential. We developed a spatially explicit agent-based simulation model to evaluate the influence of trade-offs among a suite of biological traits on the dispersal success of vagile animals in fragmented landscapes. We specifically chose traits known to influence dispersal success: speed of movement, perceptual range, risk of predation, need to forage during dispersal, and amount of suitable habitat required for successful settlement in a patch. Using the metric of relative dispersal success rate, we assessed how the costs and benefits of evolutionary investment in these biological traits varied with landscape structure. In heterogeneous environments with low habitat availability and scattered habitat patches, individuals with more equal allocation across the trait spectrum dispersed most successfully. Our analyses suggest that the dispersal success of animals in heterogeneous environments is highly dependent on hierarchical interactions between trait trade-offs and the geometric configurations of the habitat patches in the landscapes through which they disperse. In an applied sense, our results indicate potential for ecological mis-alignment between species' evolved suites of dispersal-related traits and altered environmental conditions as a result of rapid global change. In many cases identifying the processes that shape patterns of animal dispersal, and the consequences of abiotic changes for these processes, will require consideration of complex relationships among a range of organism-specific and environmental factors.