Topographic Complexity Is a Principal Driver of Plant Endemism in Mediterranean Islands.

The frequency of endemism in the flora of Mediterranean Islands does not follow a straightforward species-area relationship, and the determinants of endemism are several and complex. The aim of this study was to estimate the explanatory power of a small number of variables on the species richness of vascular plants on selected Mediterranean islands and archipelagos, and on the proportion of narrow endemism in each. We used a novel approach whereby the topographic complexity and isolation of an island were estimated through more detailed methods than those utilised previously. These parameters, along with island area and human population density, were used in a number of regression models with the number of taxa or proportion of endemics as the dependent variables. The results demonstrated that 'topography', a factor that was not specifically included in previous models for Mediterranean islands, exerted a consistent, statistically significant effect on both the number of taxa as well as the proportion of endemic taxa, in all models tested. The 'isolation' factor was not a significant predictor of the number of taxa in any of the models but was a statistically significant predictor of the proportion of endemic taxa in two of the models. The results can be used to make broad predictions about the expected number of taxa and endemics on an island, enabling the categorisation of islands as 'species-poor' or 'species-rich', potentially aiding conservation efforts.

Amphibian Speciation Rates Support a General Role of Mountains as Biodiversity Pumps.

AbstractContinental mountain areas cover <15% of global land surface, yet these regions concentrate >80% of global terrestrial diversity. One prominent hypothesis to explain this pattern proposes that high mountain diversities could be explained by higher diversification rates in regions of high topographic complexity (HTC). While high speciation in mountains has been detected for particular clades and regions, the global extent to which lineages experience faster speciation in mountains remains unknown. Here we addressed this issue using amphibians as a model system (>7,000 species), and we found that families showing high speciation rates contain a high proportion of species distributed in mountains. Moreover, we found that lineages inhabiting areas of HTC speciate faster than lineages occupying areas that are topographically less complex. When comparing across regions, we identified the same pattern in five biogeographical realms where higher speciation rates are associated with higher levels of complex topography. Low-magnitude differences in speciation rates between some low and high complex topographies suggest that high mountain diversity is also affected by low extinction and/or high colonization rates. Nevertheless, our results bolster the importance of mountains as engines of speciation at different geographical scales and highlight their importance for the conservation of global biodiversity.

An AUV localization and path planning algorithm for terrain-aided navigation.

Terrain-aided navigation (TAN) holds high potential for long-term accurate navigation of autonomous underwater vehicles (AUVs), and path planning algorithms are essential in TAN to decrease positioning errors by avoiding flat areas. This study proposed an AUV localization and path planning algorithm for TAN, which consists of a value function calculation and online path planning. In the value function calculation, the topographic complexity is treated as a factor that influences AUV state transition probabilities to calculate the optimal policy; meanwhile, the online path planning applies a particle filter to localize and command AUVs, and particle weights are calculated according to topographic complexity. Simulation experimental results demonstrate that this algorithm could provide paths with accurate TAN location results and good maneuvering performance.

Refining predictions of metacommunity dynamics by modeling species non-independence.

Predicting the dynamics of biotic communities is difficult because species' environmental responses are not independent, but covary due to shared or contrasting ecological strategies and the influence of species interactions. We used latent-variable joint species distribution models to analyze paired historical and contemporary inventories of 585 vascular plant species on 471 islands in the southwest Finnish archipelago. Larger, more heterogeneous islands were characterized by higher colonization rates and lower extinction rates. Ecological and taxonomical species groups explained small but detectable proportions of variance in species' environmental responses. To assess the potential influence of species interactions on community dynamics, we estimated species associations as species-to-species residual correlations for historical occurrences, for colorizations, and for extinctions. Historical species associations could to some extent predict joint colonization patterns, but the overall estimated influence of species associations on community dynamics was weak. These results illustrate the benefits of considering metacommunity dynamics within a joint framework, but also suggest that any influence of species interactions on community dynamics may be hard to detect from observational data.

Pelagic Subsidies Underpin Fish Productivity on a Degraded Coral Reef.

Coral reefs harbor high productivity in nutrient-poor tropical oceans. This exceptional productivity can be explained by high recycling rates [1, 2], deep-water nutrient enrichment [3], and assimilation of external production [4]. Fishes consume this productivity through multiple trophic pathways and, as a result, dominate consumer biomass. Their reliance on pelagic versus benthic productivity pathways has been quantified from the tissues of individual fish [5, 6], but the contribution of different energetic pathways to the total productivity of coral reef fish assemblages remains unquantified. Here, we combined high-resolution surveys and individual biomass production estimates to generate the first energetic map of a full coral reef fish assemblage, from the smallest to the largest fishes [7, 8]. We found that the windward section of a coral reef on the Great Barrier Reef delivered an average fish productivity of 4.7 kg ha-1 day-1, of which 41% was derived from water column photosynthesis, 29% by the epibenthic reef surface, 14% from cryptobenthic microhabitats, and 11% from adjacent sandy areas. The critical energetic contribution of pelagic subsidies would remain undetected if considering fish standing biomass alone, because the high productivity of reef planktivores originated from a relatively small biomass. Importantly, this study took place on a reef with only ∼6% of coral cover following multiple coral mortality events. Thus, our study offers hope that reefs subject to coral loss can still maintain considerable fish productivity, with planktivorous fishes providing major pelagic subsidies.

Testing the role of ancient and contemporary landscapes on structuring genetic variation in a specialist grasshopper.

Understanding the processes underlying spatial patterns of genetic diversity and structure of natural populations is a central topic in evolutionary biogeography. In this study, we combine data on ancient and contemporary landscape composition to get a comprehensive view of the factors shaping genetic variation across the populations of the scrub-legume grasshopper (Chorthippus binotatus binotatus) from the biogeographically complex region of southeast Iberia. First, we examined geographical patterns of genetic structure and employed an approximate Bayesian computation (ABC) approach to compare different plausible scenarios of population divergence. Second, we used a landscape genetic framework to test for the effects of (1) Late Miocene paleogeography, (2) Pleistocene climate fluctuations, and (3) contemporary topographic complexity on the spatial patterns of population genetic differentiation. Genetic structure and ABC analyses supported the presence of three genetic clusters and a sequential west-to-east splitting model that predated the last glacial maximum (LGM, c. 21 Kya). Landscape genetic analyses revealed that population genetic differentiation was primarily shaped by contemporary topographic complexity, but was not explained by any paleogeographic scenario or resistance distances based on climate suitability in the present or during the LGM. Overall, this study emphasizes the need of integrating information on ancient and contemporary landscape composition to get a comprehensive view of their relative importance to explain spatial patterns of genetic variation in organisms inhabiting regions with complex biogeographical histories.

Hierarchical genetic structure shaped by topography in a narrow-endemic montane grasshopper.

BACKGROUND: Understanding the underlying processes shaping spatial patterns of genetic structure in free-ranging organisms is a central topic in evolutionary biology. Here, we aim to disentangle the relative importance of neutral (i.e. genetic drift) and local adaptation (i.e. ecological divergence) processes in the evolution of spatial genetic structure of the Morales grasshopper (Chorthippus saulcyi moralesi), a narrow-endemic taxon restricted to the Central Pyrenees. More specifically, we analysed range-wide patterns of genetic structure and tested whether they were shaped by geography (isolation-by-distance, IBD), topographic complexity and present and past habitat suitability models (isolation-by-resistance, IBR), and environmental dissimilarity (isolation-by-environment, IBE). RESULTS: Different clustering analyses revealed a deep genetic structure that was best explained by IBR based on topographic complexity. Our analyses did not reveal a significant role of IBE, a fact that may be due to low environmental variation among populations and/or consequence of other ecological factors not considered in this study are involved in local adaptation processes. IBR scenarios informed by current and past climate distribution models did not show either a significant impact on genetic differentiation after controlling for the effects of topographic complexity, which may indicate that they are not capturing well microhabitat structure in the present or the genetic signal left by dispersal routes defined by habitat corridors in the past. CONCLUSIONS: Overall, these results indicate that spatial patterns of genetic variation in our study system are primarily explained by neutral divergence and migration-drift equilibrium due to limited dispersal across abrupt reliefs, whereas environmental variation or spatial heterogeneity in habitat suitability associated with the complex topography of the region had no significant effect on genetic discontinuities after controlling for geography. Our study highlights the importance of considering a comprehensive suite of potential isolating mechanisms and analytical approaches in order to get robust inferences on the processes promoting genetic divergence of natural populations.

Geographic determinants of gene flow in two sister species of tropical Andean frogs.

Complex interactions between topographic heterogeneity, climatic and environmental gradients, and thermal niche conservatism are commonly assumed to indicate the degree of biotic diversification in montane regions. Our aim was to investigate factors that disrupt gene flow between populations and to determine if there is evidence of downslope asymmetric migration in highland frogs with wide elevational ranges and thermal niches. We determined the role of putative impediments to gene flow (as measured by least-cost path (LCP) distances, topographic complexity, and elevational range) in promoting genetic divergence between populations of 2 tropical Andean frog sister species (Dendropsophus luddeckei, N = 114; Dendropsophus labialis, N = 74) using causal modeling and multiple matrix regression. Although the effect of geographic features was species specific, elevational range and LCP distances had the strongest effect on gene flow, with mean effect sizes (Mantel r and regression coefficients ß), between 5 and 10 times greater than topographic complexity. Even though causal modeling and multiple matrix regression produced congruent results, the latter provided more information on the contribution of each geographic variable. We found moderate support for downslope migration. We conclude that the climatic heterogeneity of the landscape, the elevational distance between populations, and the inability to colonize suboptimal habitats due to thermal niche conservatism influence the magnitude of gene flow. Asymmetric migration, however, seems to be influenced by life history traits.