Identifying physical and ecological boundaries that limit where species can occur is important for predicting how those species will respond to global change. The island of Borneo encompasses a wide range of habitats that support some of the highest richness on Earth, making it an ideal location for investigating ecological mechanisms underlying broad patterns of species distribution. We tested variation in richness and range-size in relation to edaphic specialization and vegetation zone boundaries using 3060 plant species from 193 families centered around the elevational gradient of Mt Kinabalu, Borneo. Across species, average range-size increased with elevation, consistent with Rapoport's rule. However, plants associated with ultramafic soil, which is low in nutrient and water availability and often has high concentrations of heavy metals, had larger range-sizes and greater richness than expected along the elevational gradient, as compared to a null model with randomization of edaphic association. In contrast, non-ultramafic species had smaller range-sizes and lower richness than expected. These results suggest that tolerance of resource limitation may be associated with wider range-sizes, whereas species intolerant of edaphic stress may have narrower range-sizes, possibly owing to more intense competition in favorable soil types. Using elevation as a predictor of average range-sizes, we found that piece-wise models with breakpoints at vegetation zone transitions explained species distributions better than models that did not incorporate ecological boundaries. The greatest relative increases in range-size with respect to elevation occurred mid-elevation, within the montane cloud forest vegetation zone. Expansion of average range-size across an area without physical boundaries may indicate a shift in ecological strategy and importance of biotic versus abiotic stressors. Our results indicate that elevational range-size patterns are structured by ecological constraints such as species' edaphic association, which may limit the ability of species to migrate up or down mountains in response to climate change.

Quelle est la réponse aux perturbations, et la limitation de l’humidité, par des taxons similaires basés sur l’hétérogénéité des micro-site de l’habitat? Pour cette étude nous avons examiné comment la disponibilité de feu et de l’humidité influence la répartition des orchidées endémiques malgaches spécifique des affleurements de granit (inselbergs). Trois ans après le passage du feu, nous avons compare les modes de distribution et l’abondance d’orchidées dans un habitat d’une mosaïque complexe de brûlures, en tenant compte de la densité par rapport à l’intensité des dégâts d’incendie et de la disponibilité de l’humidité. Les espèces du sous- tribu Angraecinae ont été sensibles au feu, mais tolérant à une disponibilité limitée de l’humidité. orchidées Angraecinae avait un modèle uniforme de la distribution influencée par la taille du tapis de végétation. Les espèces de la sous-tribu Habenariae étaient tolérants de feu, mais limitée aux pentes rocheuses humides par des écoulements d’eau. Habenariae ont été randomizes regroupés en masses compactes, influencée par des facteurs non encore identifiés. Les résultats suggèrent l’existence de différentes stratégies de survie des espèces. Il serait inexact de penser que les orchidées voisins sur un substrat de granite aurait la même réponse à des facteurs environnementaux ou de perturbation. orchidées Angraecoid sur les inselbergs sont exposés à des menaces spécifiques et doivent être considérées comme des espèces indicatrices de la conservation est prioritaire à l’avenir.

Sampling arthropods in the upper canopy of tall trees presents a range of challenges associated with portability, cost, placement, replication and collection. Detailed schematics and instructions are presented here for three trap designs: sticky CD cases, plastic bottle hanging flight-intercept traps and drink bottleneck funnel crawl traps. By using simple and salvageable materials such as plastic drink bottles and compact disc cases, the financial cost of an arthropod sampling regime in the crowns of old-growth Tasmanian stringybark trees Eucalyptus obliqua (L'Herit) was kept to a minimum. The traps collected comparatively diverse communities: the sticky traps catching high levels of Diptera, Hymenoptera and Coleoptera; the funnel traps catching Diptera, Hemiptera and Coleoptera; and the hanging traps catching Diptera, Coleoptera and Lepidoptera. The sticky traps were ranked best, and the funnels worst, when integrating relative merits of cost, transport, durability, construction, placement, retrieval, sorting and arthropod condition.

Abstract. Suitable habitat for a species is often modeled by linking its distribution patterns with landscape characteristics. However, modeling the relationship between fitness and landscape characteristics is less common. In this study we take a novel approach towards species distribution modeling (SDM) by investigating factors important not only for species occurrence, but also abundance and physical size, as well as fitness measures. We used the Neotropical terrestrial orchid Prescottia stachyodes as our focal species, and compiled geospatial information on habitat and neighboring plants for use in a two-part conditional SDM that accounted for zero inflation and reduced spatial autocorrelation bias. First, we modeled orchid occurrence, and then within suitable sites we contrasted habitat characteristics important for orchid abundance as compared to plant size. We then tested possible fitness implications, informed by analyses of allometric scaling of reproductive effort and lamina area, as well as size-density relationships in areas of P. stachyodes co-occurrence. We determined that orchid presence was based on a combination of biotic and abiotic factors (indicator species, diffuse solar radiation). Within these sites, P. stachyodes abundance was higher on flat terrain, with fine, moderately well-drained soil, and areas without other native orchids, whereas plant size was greater in less rocky areas. In turn, plant size determined reproductive effort, with floral display height proportionate to lamina area (more photosynthates); however, allometric scaling of flower quantity suggests a higher energy cost for production, or maintenance, of flowers. Overall, habitat factors most important for abundance differed from those for size (and thus reproductive effort), suggesting that sites optimal for either recruitment or survival may not be the primary source of seeds. For plots with multiple P. stachyodes plants, size-density relationships differed depending on the size class examined, which may reflect context-dependent population dynamics. Thus, ecological resolution provided by SDM can be enhanced by incorporating abundance and fitness measures.

Motility behavior of an engineered chemosensory particle (ECP) in fluidic environments is driven by its responses to chemical stimuli. One of the challenges to understanding such behaviors lies in tracking changes in chemical signal gradients of chemoattractants and ECP-fluid dynamics as the fluid is continuously disturbed by ECP motion. To address this challenge, we introduce a new multiscale numerical model to simulate chemotactic swimming of an ECP in confined fluidic environments by accounting for motility-induced disturbances in spatiotemporal chemoattractant distributions. The model accommodates advective-diffusive transport of unmixed chemoattractants, ECP-fluid hydrodynamics at the ECP-fluid interface, and spatiotemporal disturbances in the chemoattractant concentrations due to particle motion. Demonstrative simulations are presented with an ECP, mimicking Escherichia coli (E. coli) chemotaxis, released into initially quiescent fluids with different source configurations of the chemoattractants N-methyl-L-aspartate and L-serine. Simulations demonstrate that initial distributions and temporal evolution of chemoattractants and their release modes (instantaneous vs. continuous, point source vs. distributed) dictate time histories of chemotactic motility of an ECP. Chemotactic motility is shown to be largely determined by spatiotemporal variation in chemoattractant concentration gradients due to transient disturbances imposed by ECP-fluid hydrodynamics, an observation not captured in previous numerical studies that relied on static chemoattractant concentration fields.

Our goal was to interrogate Janzen’s idea that “mountain passes are higher in the tropics” by investigating putative ecological and biogeographic drivers of patterns of elevational range-sizes among equatorial plant families. We used herbarium records for sixty species-rich plant families, representing a total of 18535 species, to estimate distributions over a 4500 m elevational gradient. For each family, we estimated the change in average range-sizes with increasing elevation (i.e. Rapoport’s rule, abbreviated as ERR) and quantified 15 metrics of familial richness distribution, evolutionary age, and biogeographic affiliation. We visualized covariation across families using used phylogenetic principal components analysis (pPCA), with color illustrating endemism. We then evaluated how family-level ERR slopes correlated with each metric individually, and the first two pPCA components, using phylogenetic independent contrasts. Families with greater Sundaland endemism, or richness that was restricted to tropical lowland forests, had positive ERR slopes. Families with stronger Sahul affiliation, or montane centered richness, had shallower, neutral, or negative ERR slopes. Families with Wallacea affiliation, broader latitudinal or elevational distributions, cosmopolitanism, or older evolutionary age had mixed results. Our findings support Janzen’s hypothesis that “mountain passes are higher in the tropics.” If long term climate stability over millions of years promotes habitat specialization, then among taxa with long-term tropical affiliations, we would expect smaller range-sizes within lowland forests, with range-size expansion towards higher elevations, expressed as a positive ERR slope. Conversely, variation in growing conditions should promote larger, relatively consistent, range-sizes expressed as a neutral ERR slope. Our results support this corollary because of the dichotomy of ERR slopes observed in relation to elevational and historical biogeographic positioning, which may be an indicator of vulnerability of these plant groups to contemporary climate change.

No abstract

Our goal was to interrogate Janzen’s idea that “mountain passes are higher in the tropics” by investigating putative ecological and biogeographic drivers of patterns of elevational range-sizes among equatorial plant families. We used herbarium records for sixty species-rich plant families, representing a total of 18535 species, to estimate distributions over a 4500 m elevational gradient. For each family, we estimated the change in average range-sizes with increasing elevation (i.e. Rapoport’s rule, abbreviated as ERR) and quantified 15 metrics of familial richness distribution, evolutionary age, and biogeographic affiliation. We visualized covariation across families using used phylogenetic principal components analysis (pPCA), with color illustrating endemism. We then evaluated how family-level ERR slopes correlated with each metric individually, and the first two pPCA components, using phylogenetic independent contrasts. Families with greater Sundaland endemism, or richness that was restricted to tropical lowland forests, had positive ERR slopes. Families with stronger Sahul affiliation, or montane centered richness, had shallower, neutral, or negative ERR slopes. Families with Wallacea affiliation, broader latitudinal or elevational distributions, cosmopolitanism, or older evolutionary age had mixed results. Our findings support Janzen’s hypothesis that “mountain passes are higher in the tropics.” If long term climate stability over millions of years promotes habitat specialization, then among taxa with long-term tropical affiliations, we would expect smaller range-sizes within lowland forests, with range-size expansion towards higher elevations, expressed as a positive ERR slope. Conversely, variation in growing conditions should promote larger, relatively consistent, range-sizes expressed as a neutral ERR slope. Our results support this corollary because of the dichotomy of ERR slopes observed in relation to elevational and historical biogeographic positioning, which may be an indicator of vulnerability of these plant groups to contemporary climate change.