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Aim: Faced with the dispute regarding spatial gradients of body size in ectotherms, we build upon their long-known allometric relationship with water economy, which scales with thermal and hydric regimes, to revisit and refine the water conservation hypothesis (WCH). We provide a brief description of the WCH, including its physiological basis and geographical predictions for body size clines in terrestrial amphibians, and test it against heat-based hypotheses in four amphibian clades. Location: The Americas. Methods: We employ phylogenetic comparative analyses to examine relationships between body size and both temperature, as a descriptor of the effect of heat alone, and potential evapotranspiration, which describes the water constraint along evaporative gradients. We assess these relationships in four amphibian clades: the subfamily of leaf frogs (Phyllomedusinae), genera of gladiator frogs (Hypsiboas), salamanders (Plethodon) and the family of glass frogs (Centrolenidae). Results: Three clades did not show phylogenetic signals in body size variation. In addition, three clades showed a positive relationship with potential evapotranspiration as predicted, and all of them were unrelated to temperature. When present, however, the explanatory power of evaporative energy on body size variation was relatively weak. Main conclusions: The conservation of water across evaporative gradients is both a more comprehensive explanation and a more pervasive driver of spatial clines in body size among terrestrial amphibians than is the balance of heat alone. However, the relatively low predictive ability of evaporative energy and its dependence on specific climatic configurations both emphasize and elucidate the non-universality of the phenomenon.

Geographic gradients in the species richness of non‐human primates have traditionally been attributed to the variation in forest productivity (related to precipitation levels), although an all‐inclusive, global‐scale analysis has never been conducted. We perform a more comprehensive test on the role of precipitation and biomass production and propose an alternative hypothesis – the variation in vertical structure of forest habitats as measured by forest canopy height – in determining primate species richness on a global scale. Considering the potential causal relationships among precipitation, productivity and forest structure, we arranged these variables within a path framework to assess their direct and indirect associations with the pattern of primate species richness using structural equation modelling. The analysis also accounted for the influence of spatial autocorrelation in the relationships and assessed possible historical differences among biogeographical regions. The path coefficients indicate that forest canopy height (used as a proxy for vertical forest structure) is a better predictor of primate species richness than either precipitation or productivity on both global and continental scales. The only exception was Asia, where precipitation prevailed, albeit independently from productivity or forest structure. The influence of spatially structured processes varied markedly among biogeographical regions. Our results challenge the traditional rainfall‐based viewpoint in favour of forest distribution and structure as primary drivers of primate species richness, which aggregate potential effects from both climatic factors and habitat complexity. These findings may support predictions of the impact of forest removal on primate species richness.

Conflicting hypotheses regarding the factors underlying the invasibility of plant species persist, as portrayed by Darwin’s naturalization conundrum. This is particularly critical in arid and semiarid ecosystems, for which understanding remains elusive. We test how similarities between exotic and native plants in the Brazilian semiarid Caatinga affect the invasion stage and distribution of invasive species. We estimate diversity fields for exotic species, representing the composition of native species that co-occur with each exotic species and calculated phylogenetic metrics of the distance of focal species to its field. We also assess whether changes in stage from exotic to naturalized and from naturalized to invasive are influenced by phylogenetic relatedness and functional traits. We also test whether the observed phylogenetic distance values of the invasive species differ from those expected by chance. Finally, we analyze whether there are functional similarities between the stages of exotic species and native plants. Plants that are phylogenetically closer to the more frequent native species of the Caatinga are more likely to become naturalized and invasive. Among invasive species with a significant pattern of phylogenetic relatedness, those that are closer to native species are more prevalent. Naturalized and invasive plants are shorter and have smaller leaves and seeds than native plants. The observed functional differences suggest that naturalized and invasive species adopt strategies similar to those of competitive native plants, such as seed bank formation and dense populations.

Species richness and range size are key features of biogeographic and macroecological analyses, which can yield a first assessment tool to define conservation priorities. Here we combined both features in a simultaneous analysis, based on range-diversity plots, to identify sets of rich-rare (high species richness with restricted ranges) and poor-rare cells (low species richness with restricted ranges). We applied this analysis to the anurans of South America and evaluated the representation of those sets of cells within the protected area system. South American anurans showed high species richness in the Brazilian Atlantic Forest and East Tropical Andes, while regions harboring most of the rare species were concentrated in the Andes and Atlantic Coast from North-Eastern Brazil to River Plate. Based on such patterns, we identified as rich-rare cells the Brazilian Atlantic Forest and Tropical Andes and as poor-rare cells the southern part of Andes and Uruguay. A low fraction of both sets of cells was represented within the protected area system. We show that a simultaneous consideration of species richness and rarity provides a rapid assessment of large-scale biodiversity patterns and may contribute to the definition of conservation priorities.

The origin of morphological diversity is a critical question in evolutionary biology. Interactions between the environment and developmental processes have determining roles in morphological diversity, creating patterns through space and over time. Also, the shape of organisms tends to vary with increasing size as a result of those developmental processes, known as allometry. Several studies have demonstrated that the body sizes of anurans are associated with hydric conditions in their environments and that localities with high water stress tend to select for larger individuals. However, how environmental conditions alter those patterns of covariance between size and shape is still elusive. We used 3D geometric morphometric analyses, associated with phylogenetic comparative methods, to determine if the morphological variations and allometric patterns found in Arboranae (Anura) is linked to water conservation mechanisms. We found effects of the hydric stress on the shape of Arboranae species, favouring globular shapes. Also, the allometric patterns varied in intensity according to the water stress gradient, being particularly relevant for smaller frogs, and more intense in environments with higher water deficits. Our study provides empirical evidence that more spherical body shapes, especially among smaller species, reflect an important adaptation of anurans to water conservation in water-constrained environments.

Body size and shape fundamentally determine organismal energy requirements by modulating heat and mass exchange with the environment and the costs of locomotion, thermoregulation, and maintenance. Ecologists have long used the physical linkage between morphology and energy balance to explain why the body size and shape of many organisms vary across climatic gradients, e.g., why larger endotherms are more common in colder regions. However, few modeling exercises have aimed at investigating this link from first principles. Body size evolution in bats contrasts with the patterns observed in other endotherms, probably because physical constraints on flight limit morphological adaptations. Here, we develop a biophysical model based on heat transfer and aerodynamic principles to investigate energy constraints on morphological evolution in bats. Our biophysical model predicts that the energy costs of thermoregulation and flight, respectively, impose upper and lower limits on the relationship of wing surface area to body mass (S-MR), giving rise to an optimal S-MR at which both energy costs are minimized. A comparative analysis of 278 species of bats supports the model’s prediction that S-MR evolves toward an optimal shape and that the strength of selection is higher among species experiencing greater energy demands for thermoregulation in cold climates. Our study suggests that energy costs modulate the mode of morphological evolution in bats—hence shedding light on a long-standing debate over bats’ conformity to ecogeographical patterns observed in other mammals—and offers a procedure for investigating complex macroecological patterns from first principles.

Geographical gradients of body size express climate-driven constraints on animals, but whether they exist and what causes them in ectotherms remains contentious. For amphibians, the water conservation hypothesis posits that larger bodies reduce evaporative water loss (EWL) along dehydrating gradients. To address this hypothesis mechanistically, we build on well-established biophysical equations of water exchange in anurans to propose a state-transition model that predicts an increase of either body size or resistance to EWL as alternative specialization along dehydrating gradients. The model predicts that species whose water economy is more sensitive to variation in body size than to variation in resistance to EWL should increase in size in response to increasing potential evapotranspiration (PET). To evaluate the model predictions, we combine physiological measurements of resistance to EWL with geographic data of body size for four different anuran species. Only one species, Dendropsophus minutus, was predicted to exhibit a positive body size–PET relationship. Results were as predicted for all cases, with one species—Boana faber—showing a negative relationship. Based on an empirically verified mathematical model, we show that clines of body size among anurans depend on the current values of those traits and emerge as an advantage for water conservation. Our model offers a mechanistic and compelling explanation for the cause and variation of gradients of body size in anurans.

China is facing an unprecedented set of challenges in balancing the effects of economic development and global climate change with environmental protection and maintaining biodiversity. Although positive steps have been undertaken to remedy this situation, currently 80% of China’s 25 extant primate species are threatened, 15–18 species have population sizes of less than 3000 individuals, and two species of gibbons and one species of langur have been extirpated over the past few decades. Today, virtually all species of primates in China inhabit fragmented landscapes and are distributed in small isolated subpopulations with limited opportunities to exchange individuals or genetic information. Here we present a historical framework examining how human-induced environmental changes, particularly since the second half of the 20th century, accelerated primate population decline in China. In addition, we modeled the expected spatial conflict between agricultural expansion and primate distributions over the next 25–75 years and assessed the current overlap between protected areas and primate distributions. Depending on the assumptions of the spatial conflict model, primate distributions are expected to decline by an additional 51–87% by the year 2100. Thus, unless large-scale conservation policies are implemented immediately the current trend of primate population decline, local extirpation, and species extinctions will accelerate. To mitigate against such extinction scenarios, we advocate the creation of a Chinese national agency and repository of environmental information focused on public awareness and education, the implementation of targeted programs of habitat restoration designed to return impacted forests to a more natural state especially within and at the boundaries of nature reserves, the establishment of additional protect areas, and the construction of a latticework of corridors connecting isolated primate subpopulations. This comprehensive approach offers the most effective way to protect China’s animal and plant biodiversity, including its endangered primate populations.

Primates occur in 90 countries, but four—Brazil, Madagascar, Indonesia, and the Democratic Republic of the Congo (DRC)—harbor 65% of the world’s primate species (439) and 60% of these primates are Threatened, Endangered, or Critically Endangered (IUCN Red List of Threatened Species 2017-3). Considering their importance for global primate conservation, we examine the anthropogenic pressures each country is facing that place their primate populations at risk. Habitat loss and fragmentation are main threats to primates in Brazil, Madagascar, and Indonesia. However, in DRC hunting for the commercial bushmeat trade is the primary threat. Encroachment on primate habitats driven by local and global market demands for food and non-food commodities hunting, illegal trade, the proliferation of invasive species, and human and domestic-animal borne infectious diseases cause habitat loss, population declines, and extirpation. Modeling agricultural expansion in the 21st century for the four countries under a worst-case-scenario, showed a primate range contraction of 78% for Brazil, 72% for Indonesia, 62% for Madagascar, and 32% for DRC. These pressures unfold in the context of expanding human populations with low levels of development. Weak governance across these four countries may limit effective primate conservation planning. We examine landscape and local approaches to effective primate conservation policies and assess the distribution of protected areas and primates in each country. Primates in Brazil and Madagascar have 38% of their range inside protected areas, 17% in Indonesia and 14% in DRC, suggesting that the great majority of primate populations remain vulnerable. We list the key challenges faced by the four countries to avert primate extinctions now and in the future. In the short term, effective law enforcement to stop illegal hunting and illegal forest destruction is absolutely key. Long-term success can only be achieved by focusing local and global public awareness, and actively engaging with international organizations, multinational businesses and consumer nations to reduce unsustainable demands on the environment. Finally, the four primate range countries need to ensure that integrated, sustainable land-use planning for economic development includes the maintenance of biodiversity and intact, functional natural ecosystems.