Scale dependence in species turnover reflects variance in species occupancy

Patterns of species turnover may reflect the processes driving community dynamics across scales. While the majority of studies on species turnover have examined pairwise comparison metrics (e.g., the average Jaccard dissimilarity), it has been proposed that the species-area relationship (SAR) also offers insight into patterns of species turnover because these two patterns may be analytically linked. However, these previous links only apply in a special case where turnover is scale invariant, and we demonstrate across three different plant communities that over 90% of the pairwise turnover values are larger than expected based on scale-invariant predictions from the SAR. Furthermore, the degree of scale dependence in turnover was negatively related to the degree of variance in the occupancy frequency distribution (OFD). These findings suggest that species turnover diverges from scale invariance, and as such pairwise turnover and the slope of the SAR are not redundant. Furthermore, models developed to explain the OFD should be linked with those developed to explain species turnover to achieve a more unified understanding of community structure

Characterizing avian survival along a rural-to-urban land use gradient

Many avian species persist in human-dominated landscapes; however, little is known about the demographic consequences of urbanization in these populations. Given that urban habitats introduce novel benefits (e.g., anthropogenic resources) and pressures (e.g., mortality risks), conflicting mechanisms have been hypothesized to drive the dynamics of urban bird populations. Top-down processes such as predation predict reduced survivorship in suburban and urban habitats, whereas bottom-up processes, such as increased resource availability, predict peak survival in suburban habitats. In this study, we use mark–recapture data of seven focal species encountered between 2000 and 2012 to test hypotheses about the processes that regulate avian survival along an urbanization gradient in greater Washington, D.C., USA. American Robin, Gray Catbird, Northern Cardinal, and Song Sparrow exhibited peak survival at intermediate and upper portions of the rural-to-urban gradient; this pattern supports the hypothesis that bottom-up processes (e.g., resource availability) can drive patterns of avian survival in some species. In contrast, Carolina Chickadee showed no response and Carolina and House Wren showed a slightly negative response to urban land cover. These contrasting results underscore the need for comparative studies documenting the mechanisms that drive demography and how those factors differentially affect urban adapted and urban avoiding species

Species Richness at Continental Scales Is Dominated by Ecological Limits

Abstract Explaining variation in species richness among provinces and other large geographic regions remains one of the most challenging problems at the intersection of ecology and evolution. Here we argue that empirical evidence supports a model whereby ecological factors associated with resource availability regulate species richness at continental scales. Any large-scale predictive model for biological diversity must explain three robust patterns in the natural world. First, species richness for evolutionary biotas is highly correlated with resource-associated surrogate variables, including area, temperature, and productivity. Second, species richness across epochal timescales is largely stationary in time. Third, the dynamics of diversity exhibit clear and predictable responses to mass extinctions, key innovations, and other perturbations. Collectively, these patterns are readily explained by a model in which species richness is regulated by diversity-dependent feedback mechanisms. We argue that many purported tests of the ecological limits hypothesis, including branching patterns in molecular phylogenies, are inherently weak and distract from these three core patterns. We have much to learn about the complex hierarchy of processes by which local ecological interactions lead to diversity dependence at the continental scale, but the empirical evidence overwhelmingly suggests that they do

Heterospecific interactions and the proliferation of sexually dimorphic traits

Sexual selection is expected to promote speciation by fostering the evolution of sexual traits that minimize reproductive interactions among existing or incipient species. In species that compete for access to, or attention of, females, sexual selection fosters more elaborate traits in males compared to females. If these traits also minimize reproductive interactions with heterospecifics, then species with enhanced risk of interactions between species might display greater numbers of these sexual dimorphic characters. We tested this prediction in eight families of North American birds. In particular, we evaluated whether the number of sexually dimorphic traits was positively associated with species richness at a given site or with degree of sympatry with congeners. We found no strong evidence of enhanced sexual dimorphism with increasing confamilial species richness at a given site. We also found no overall relationship between the number of sexually dimorphic traits and overlap with congeners across these eight families. However, we found patterns consistent with our prediction within Anatidae (ducks, geese and swans) and, to a lesser degree, Parulidae (New World warblers). Our results suggest that sexually selected plumage traits in these groups potentially play a role in reproductive isolation

On the processes generating latitudinal richness gradients: identifying diagnostic patterns and predictions

We use a simulation model to examine four of the most common hypotheses for the latitudinal richness gradient and identify patterns that might be diagnostic of those four hypotheses. The hypotheses examined include (1) tropical niche conservatism, or the idea that the tropics are more diverse because a tropical clade origin has allowed more time for diversification in the tropics and has resulted in few species adapted to extra-tropical climates. (2) The ecological limits hypothesis suggests that species richness is limited by the amount of biologically available energy in a region. (3) The speciation rates hypothesis suggests that the latitudinal gradient arises from a gradient in speciation rates. (4) Finally, the tropical stability hypothesis argues that climatic fluctuations and glacial cycles in extratropical regions have led to greater extinction rates and less opportunity for specialization relative to the tropics. We found that tropical niche conservatism can be distinguished from the other three scenarios by phylogenies which are more balanced than expected, no relationship between mean root distance (MRD) and richness across regions, and a homogeneous rate of speciation across clades and through time. The energy gradient, speciation gradient, and disturbance gradient scenarios all produced phylogenies which were more imbalanced than expected, showed a negative relationship between MRD and richness, and diversity-dependence of speciation rate estimates through time. We found that the relationship between speciation rates and latitude could distinguish among these three scenarios, with no relation expected under the ecological limits hypothesis, a negative relationship expected under the speciation rates hypothesis, and a positive relationship expected under the tropical stability hypothesis. We emphasize the importance of considering multiple hypotheses and focusing on diagnostic predictions instead of predictions that are consistent with multiple hypotheses

Genetic diversity and thermal performance in invasive and native populations of African fig flies

During biological invasions, invasive populations can suffer losses of genetic diversity that are predicted to negatively impact their fitness/performance. Despite examples of invasive populations harboring lower diversity than conspecific populations in their native range, few studies have linked this lower diversity to a decrease in fitness. Using genome sequences, we show that invasive populations of the African fig fly, Zaprionus indianus, have less genetic diversity than conspecific populations in their native range and that diversity is proportionally lower in regions of the genome experiencing low recombination rates. This result suggests that selection may have played a role in lowering diversity in the invasive populations. We next use interspecific comparisons to show that genetic diversity remains relatively high in invasive populations of Z. indianus when compared to other closely related species. By comparing genetic diversity in orthologous gene regions, we also show that the genome-wide landscape of genetic diversity differs between invasive and native populations of Z. indianus, indicating that invasion not only affects amounts of genetic diversity, but also how that diversity is distributed across the genome. Finally, we use parameter estimates from thermal performance curves measured for 13 species of Zaprionus to show that Z. indianus has the broadest thermal niche of measured species, and that performance does not differ between invasive and native populations. These results illustrate how aspects of genetic diversity in invasive species can be decoupled from measures of fitness, and that a broad thermal niche may have helped facilitate Z. indianus's range expansion.Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: Dimensions of Biodiversity award number 1737752Data used to generate genome annotations was generated by extracting whole RNA from groups of ~5 adult flies (24 hours after eclosion). Transcripts were assembed using Trinity (Grabherr et al. 2011; Hass et al. 2013) and annotations were generated using the MAKER pipeline (v3.01.02; Holt and Yandell 2011; Campbell et al. 2014). Data on thermal performance we generated in the lab under controlled conditions. All scripts used to fit thermal performance curves are given in this Dryad deposit. Software available for the method used are available at github.com/silastittes/performr

Multiple dimensions of niche specialization explain changes in species’ range area, occupancy, and population size

In response to environmental change, species may decrease or increase in population size across their range, expand or contract their range limits, or alter how sites are occupied within their existing range. Shifts in range limits and widespread changes in population size have been documented in birds especially in response to changes in climate. Range occupancy, or how patchily or continuously a species is distributed within their range, has been studied less in the context of anthropogenic changes but may be expected to decrease with range-wide population size if abundance-occupancy relationships are generally positive. Determining which properties of species are related to range expansion or contraction or increased range occupancy or decreased range occupancy is useful in developing an understanding of which species become “winners” or “losers” under global change. Species with broader climatic niches may be more likely to successfully expand to new sites as climate changes. Range occupancy can be related to habitat preferences of species, and habitat specialization may predict how species fill in sites within their range. To examine how species niche breadth may explain changes in species distributions, we modeled how changes in range-wide population size, range extent, and range occupancy from 1976 to 2016 were predicted by species’ climate, habitat, and diet niche breadth for 77 North American breeding bird species. We found that climate generalists were more likely to be increasing in range area, while species with declining population trends were likely to be contracting in range area and in occupancy within their range. Understanding how different dimensions of specialization relate to shifts in species distributions may improve predictions of which species are expected to benefit from or be vulnerable to anthropogenic change

3 dimensional proton beam writing for micro electromechanical systems applications.

Proton beam writing is a direct write lithographic technique that uses finely focused MeV proton beams to create structures in a target material. The depth the protons travel in a material is dependent on its energy, this unique property of proton beams allow multi level structures to be created in materials. PBW has been demonstrated successfully on semiconductor materials, glass and polymers. This thesis is a study of the application of PBW in creating Micro Electro-Mechanical Systems (MEMS) in a polymer SU 8 and SU 8 polymer nano composite with silver, and shows experimental steps, theory and computer simulations involved in creating an electrostatic actuated micro-gripping device. Proton beam writing in silver SU 8 composite results in the creation of electrically conducting microstructures. The unique predictability of the range of protons in materials is leveraged in the creating of free standing conducting cantilevers structures which are used as the building blocks for a micro gripping device. The electrostatic actuation has been modelled using a finite element modelling software Sugar 3.1, and the results are comparable with actual actuations in a realized micro-gripping device

Caterpillars Count! A Citizen Science Project for Monitoring Foliage Arthropod Abundance and Phenology

'Caterpillars Count!' is a citizen science project that allows participants to collect data on the seasonal timing, or phenology, of foliage arthropods that are important food resources for forest birds. This project has the potential to address questions about the impacts of climate change on birds over biogeographic scales. Here, we provide a description of the project’s two survey protocols, evaluate the impact of survey methodology on results, compare findings made by citizen scientist participants versus trained scientists, and identify the minimum levels of sampling frequency and intensity needed to accurately capture phenological dynamics. We find that beat sheet surveys and visual surveys yield similar relative and absolute density estimates of different arthropod groups, with beat sheet surveys recording a higher frequency of beetles and visual surveys recording a higher frequency of flies. Citizen scientists generated density estimates within 6% of estimates obtained by trained scientists regardless of survey method. However, patterns of phenology were more consistent between citizen scientists and trained scientists when using beat sheet surveys than visual surveys. By subsampling our survey data, we found that conducting 30 foliage surveys on a weekly basis led to 95% of peak caterpillar date estimates to fall within one week of the “true” peak. We demonstrate the utility of 'Caterpillars Count!' for generating a valuable dataset for ecological research, and call for future studies to evaluate how training and resource materials impact data quality and participant learning gains