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1. Sky, sea, and forest islands: Diversification in the African leaf‐folding frog Afrixalus paradorsalis (Anura: Hyperoliidae) of the Lower Guineo‐Congolian rain forest

   https://doi.org/10.1111/jbi.13365  

   Charles, Kristin L. ; Bell, Rayna C. ; Blackburn, David C. ; Burger, Marius ; Fujita, Matthew K. ; Gvoždík, Václav ; Jongsma, Gregory F. M. ; Kouete, Marcel Talla ; Leaché, Adam D. ; Portik, Daniel M. ( June 2018 , Journal of Biogeography)

   To investigate how putative barriers, forest refugia, and ecological gradients across the lower Guineo‐Congolian rain forest shape genetic and phenotypic divergence in the leaf‐folding frogAfrixalus paradorsalis, and examine the role of adjacent land bridge and sky‐islands in diversification.

   The Lower Guineo‐Congolian Forest, the Cameroonian Volcanic Line (CVL), and Bioko Island, Central Africa.

   Afrixalus paradorsalis(Family: Hyperoliidae), an African leaf‐folding frog.

   We used molecular and phenotypic data to investigate diversity and divergence among theA. paradorsalisspecies complex distributed across lowland rain forests, a land bridge island, and mountains in Central Africa. We examined the coincidence of population boundaries, landscape features, divergence times, and spatial patterns of connectivity and diversity, and subsequently performed demographic modelling using genome‐wide SNP variation to distinguish among divergence mechanisms in mainland (riverine barriers, forest refugia, ecological gradients) and land bridge island populations (vicariance, overwater dispersal).

   We detected four genetically distinct allopatric populations corresponding to Bioko Island, the CVL, and two lowland rain forest populations split by the Sanaga River. Although lowland populations are phenotypically indistinguishable, pronounced body size evolution occurs at high elevation, and the timing of the formation of the high elevation population coincides with mountain uplift in the CVL. Spatial analyses and demographic modelling revealed population divergence across mainland Lower Guinea is best explained by forest refugia rather than riverine barriers or ecological gradients, and that the Bioko Island population divergence is best explained by vicariance (marine incursion) rather than overseas dispersal.

   We provide growing support for the important role of forest refugia in driving intraspecific divergences in the Guineo‐Congolian rain forest. InA. paradorsalis, sky‐islands in the CVL have resulted in greater genetic and phenotypic divergences than marine incursions of the land bridge Bioko Island, highlighting important differences in patterns of island‐driven diversification in Lower Guinea.

    

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2. Patterns and drivers of leaf‐litter ant diversity along a tropical elevational gradient in Mexico

   https://doi.org/10.1111/jbi.14217  

   Pérez‐Toledo, Gibrán Renoy ; Valenzuela‐González, Jorge E. ; Moreno, Claudia E. ; Villalobos, Fabricio ; Silva, Rogerio R. ( August 2021 , Journal of Biogeography)

   Given their high environmental variation over relatively short distances, mountains represent ideal systems for evaluating potential factors shaping diversity gradients. Despite a long‐standing interest in ecological gradients, ant diversity patterns and their related mechanisms occurring on mountains are still not well understood. Here, we (i) describe species diversity patterns (α and β) of leaf‐litter ants along the eastern slope of Cofre de Perote in Veracruz, Mexico; and (ii) evaluate climatic and spatial factors in determining these patterns.

   Veracruz, Mexico.

   Leaf‐litter ants.

   We sampled 320 m²of leaf litter spread across eight equally spaced sites from sea level to 3500 m of elevation. We used regression models to predict α‐diversity patterns with climatic (temperature and precipitation) and spatial (geometric constraints) variables. We also assessed, through multiple regression based on distance matrices (MRM), the relative importance of habitat filtering and dispersal limitations for shaping total dissimilarity (βsor), turnover (βsim) and nestedness (βnes).

   A hump‐shaped pattern was observed in the α‐diversity. This pattern is best explained by the temperature gradient. β‐diversity showed a nonlinear pattern along the elevational gradient with total dissimilarity and turnover components better explained by habitat filtering (i.e. temperature distances). Turnover had higher contribution to total dissimilarity rather than the nestedness component.

   The significance effect of temperature on both α‐ and β‐diversity patterns reinforces its widespread importance in shaping litter ant diversity patterns across elevational gradients. The hump‐shaped pattern in species richness is probably the result of harsh abiotic conditions at the base and the top of the mountain combined with biotic attrition in lowland sites. The niche specialization of ant species in their optimal thermal zones may explain total dissimilarity and ant species replacement along the studied gradient. Taken all together, these results suggest a high relevance of temperature‐driven mechanisms in the origin and maintenance of the biodiversity of such insects and probably another ectothermic taxa.

    

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3. Untangling the importance of niche breadth and niche position as drivers of tree species abundance and occupancy across biogeographic regions

   https://doi.org/10.1111/geb.13139  

   Vela Díaz, Dilys M. ; Blundo, Cecilia ; Cayola, Leslie ; Fuentes, Alfredo F. ; Malizia, Lucio R. ; Myers, Jonathan A. ; Pither, ed., Jason ( June 2020 , Global Ecology and Biogeography)

   Ecological niches shape species commonness and rarity, yet, the relative importance of different niche mechanisms within and across ecosystems remains unresolved. We tested the influence of niche breadth (range of environmental conditions where species occur) and niche position (marginality of a species’ environmental distribution relative to the mean environmental conditions of a region) on tree‐species abundance and occupancy across three biogeographic regions.

   Argentinian Andes; Bolivian Amazon; Missouri Ozarks.

   2002–2010.

   Trees.

   We calculated abiotic‐niche breadths and abiotic‐niche positions using 16 climate, soil and topographic variables. For each region, we used model selection to test the relative influence of niche breadth and niche position on local abundance and occupancy in regional‐scale networks of 0.1‐ha forest plots. To account for species–environment associations caused by other mechanisms (e.g., dispersal), we used null models that randomized associations between species occurrences and environmental variables.

   We found strong support for the niche‐position hypothesis. In all regions, species with higher local abundance and occupancy occurred in non‐marginal environments. Observed relationships between occupancy and niche position also differed from random species–environment associations in all regions. Surprisingly, we found little support for the niche‐breadth hypothesis. Observed relationships between both local abundance and niche breadth, and occupancy and niche breadth, did not differ from random species–environment associations.

   Niche position was more important than niche breadth in shaping species commonness and rarity across temperate, sub‐tropical and tropical forests. In all forests, tree species with widespread geographic distributions were associated with environmental conditions commonly found throughout the region, suggesting that niche position has similar effects on species occupancy across contrasting biogeographic regions. Our findings imply that conservation efforts aimed at protecting populations of common and rare tree species should prioritize conservation of both common and rare habitats.

    

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4. Phylogenetic diversity of two geographically overlapping lichens: isolation by distance, environment, or fragmentation?

   https://doi.org/10.1111/jbi.14033  

   Moncada, Bibiana ; Mercado‐Díaz, Joel A. ; Magain, Nicolas ; Hodkinson, Brendan P. ; Smith, Clifford W. ; Bungartz, Frank ; Pérez‐Pérez, Rosa‐Emilia ; Gumboski, Emerson ; Sérusiaux, Emmanuël ; Lumbsch, H. Thorsten ; et al ( January 2021 , Journal of Biogeography)

   Phylogenetic diversification is a precursor to speciation, but the underlying patterns and processes are not well‐studied in lichens. Here we investigate what factors drive diversification in two tropical, morphologically similar macrolichens that occupy a similar range but differ in altitudinal and habitat preferences, testing for isolation by distance (IBD), environment (IBE), and fragmentation (IBF).

   Neotropics, Hawaii, Macaronesia.

   Sticta andina,S. scabrosa(Peltigeraceae).

   We analysed 395 specimens from 135 localities, using the fungal ITS barcoding marker to assess phylogenetic diversification, through maximum likelihood tree reconstruction, TCS haplotype networks, and Tajima's D. Mantel tests were employed to detect structure in genetic vs. geographic, environmental, and fragmentation distances. Habitat preferences were quantitatively assessed by statistical analysis of locality‐based BIOclim variables.

   Sticta andinaexhibited high phenotypic variation and reticulate phylogenetic diversity across its range, whereas the phenotypically uniformS. scabrosacontained two main haplotypes, one unique to Hawaii.Sticta andinais restricted to well‐preserved andine forests and paramos, naturally fragmented habitats due to disruptive topology, whereasS. scabrosathrives in lowland to lower montane zones in exposed or disturbed microsites, representing a continuous habitat.Sticta scabrosashowed IBD only across its full range (separating the Hawaiian population) but not within continental Central and South America, there exhibiting a negative Tajima's D.Sticta andinadid not exhibit IBD but IBE at continental level and IBF in the northern Andes.

   Autecology, particularly preference for either low or high altitudes, indirectly drives phylogenetic diversification. Low diversification in the low altitude species,S. scabrosa, can be attributed to rapid expansion and effective gene flow across a more or less continuous niche due to disturbance tolerance. In contract, high diversification in the high altitude species,S. andina, can be explained by niche differentiation (IBE) and fragmentation (IBF) caused by the Andean uplift.

    

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5. Local and regional drivers of taxonomic homogenization in stream communities along a land use gradient

   https://doi.org/10.1111/geb.12976  

   Budnick, William R. ; Leboucher, Thibault ; Belliard, Jérôme ; Soininen, Janne ; Lavoie, Isabelle ; Pound, Katrina ; Jamoneau, Aurélien ; Tison‐Rosebery, Juliette ; Tales, Evelyne ; Pajunen, Virpi ; et al ( July 2019 , Global Ecology and Biogeography)

   The interaction of land use with local versus regional processes driving biological homogenization (β‐diversity loss) is poorly understood. We explored: (a) stream β‐diversity responses to land cover (forest versus agriculture) in terms of physicochemistry and physicochemical heterogeneity; (b) whether these responses were constrained by the regional species pool, i.e. γ‐diversity, or local assembly processes through local (α) diversity; (c) whether local assembly operated through the regional species abundance distribution (SAD) or intraspecific spatial aggregation; and (d) the dependence on body size, dispersal capacity and trophic level (producer versus consumer).

   USA, Canada and France.

   1993–2012.

   Stream diatoms, insects and fish.

   We analysed six datasets totalling 1,225 stream samples. We compared diversity responses to eutrophication and physicochemical heterogeneity in forested versus agricultural streams with regression methods. Null models quantified the contribution of local assembly to β‐diversity (β‐deviance, β_DEV) for both types of land covers and partitioned it into fractions explained by the regional SAD (β_SAD) versus aggregation (β_AGG).

   Eutrophication explained homogenization and more uneven regional SADs across groups, but local and regional biodiversity responses differed across taxa. The β_DEVwas insensitive to land use. The β_SADlargely exceeded β_AGGand was higher in agriculture.

   Eutrophication but not physicochemical heterogeneity of agricultural streams underlay β‐diversity loss in diatoms, insects and fish. Agriculture did not constrain the magnitude of local versus regional effects on β‐diversity but controlled the local assembly mechanisms. Although the SAD fraction dominated in both land covers, it increased further in agriculture at the expense of aggregation. Notably, the regional SADs were more uneven in agriculture, exhibiting excess common species or stronger dominance. Diatoms and insects diverged from fish in terms of biodiversity, SAD shape and β_DEVpatterns, suggesting an overriding role of body size and/or dispersal capacity compared with trophic position.

    

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