A functional perspective for global amphibian conservation

Highlights

• Human disturbances differentially threaten amphibian's ecomorphs.

• We identified key regions for the conservation of amphibian life forms.

• Torrential is a strongly vulnerable and threatened ecomorph.

Abstract

In anurans, habitat requirements strongly influence morphological evolution, resulting in ecomorphological groups. Current policy for amphibian conservation usually builds on species, without considering to the distinct vulnerability among ecomorphs. With nearly 40% of the amphibian species currently threatened with extinction, different conservation perspectives are essential to protect them. Here, we provide a global overview and future forecast of the threat level imposed on amphibian microhabitat-related ecomorphs. We analyzed the patterns of distribution of seven ecomorphs totaling 3138 species (aquatic, semi-aquatic, arboreal, semi-arboreal, burrowing, terrestrial, and torrential), related these patterns with current and likely future human-dominated landscapes, and estimated the overlap of ecomorph distribution with existing protected areas (PAs). Our results evidence key regions for amphibian conservation under the ecomorphological perspective. In these key regions, coexist more than a half of the world's ecomorphs, some of them in imperiled regions such as the Brazilian Atlantic Forest. Our results also showed that current PAs are inefficient to represent all amphibian life forms. In fact, 53% of the species have less than 1% of their distribution occurring inside PAs. This picture seems to be alarming to the most restricted and endemic ecomorph (Torrential species), which are limited to areas where increasing human-driven land transformation are expected. Considering these results, the future of some amphibian life forms may be uncertain unless urgent conservation actions are taken, such as the establishment of new conservation areas that encompasses all levels of amphibian diversity.

Introduction

A functional view of biodiversity offers a link between species traits (which are ultimately expressed in the phenotypes of individual organisms), the role they fulfill in ecosystems and their response to human disturbance (Diaz and Cabido, 2001). Such perspectives have changed the way we look at traditional conservation, given that it integrates biodiversity not only by its evolutionary history but also by its role in ecosystems functioning, and therefore, plan its conservation accordingly (Brum et al., 2017).

For anurans, in particular, habitat preference and requirements exert a strong influence on morphological evolution, being the cause of adaptive convergences in phenotypes (Moen et al., 2016; Moen and Wiens, 2017). Five microhabitat-related ecomorphs (i.e. aquatic, arboreal, burrowing, terrestrial and torrential) have evolved repeatedly in different times and locations, and species within these ecomorphs share phenotypic traits relating to vertical stratification and microhabitat use (Moen and Wiens, 2017; Oliveira and Scheffers, 2018). The geographical distribution of these microhabitat-related ecomorphs is strongly related to patterns of precipitation and temperature, and with variations in vegetation structure at a global scale (Oliveira and Scheffers, 2018). Most ecomorphs (aquatic, arboreal or semi-arboreal) are diverse only in tropical regions with a high precipitation and low annual seasonality, while some ecomorphs (as semi-aquatic or terrestrial) are climatically generalist and therefore widely distributed. In contrast, burrowing species only occur in climatic regimes with a high annual precipitation seasonality, and so, has a peculiar distribution. Finally, there is a very restricted ecomorph (torrential), distributed in some particular tropical regions (Oliveira and Scheffers, 2018). Thus, ecomorphs represent a relevant functional trait for understanding amphibian diversity based on microhabitat use. Despite the fact that amphibians are the focus of many studies in biological conservation (Hof et al., 2011; Nori et al., 2015; Stuart, 2004), as far as we know, none of them are based on the functional perspective at a global scale.

The study of causes and consequences of the global decline in amphibian populations has become a relevant research topic in conservation biology since the 90s (Wake, 1991). Amphibians are undergoing an extinction crisis; out of the 7876 living extant species (Frost, 2018), nearly 40% are currently threatened with extinction (Hoffmann et al., 2010; Jenkins et al., 2013; Pimm et al., 2014; Stuart, 2004). On top of that, it is well documented that the global network of protected areas (PAs) could be much more efficient than they really are today in protecting threatened amphibians (Nori et al., 2015; Rodrigues et al., 2004; Sánchez-Fernández and Abellán, 2015). Besides, more than 40% of non-threatened amphibians are still poorly known by science, and presumably most of them face the same threats (Hof et al., 2011; Howard and Bickford, 2014; Morais et al., 2013; Nori and Loyola, 2015; Nori et al., 2018).

Currently, the main threat to vertebrate species is the degradation (and eventually the loss) of their original habitats, with land conversion for agriculture expansion being the main driver of population decline and species loss (Grooten and Almond, 2018). Amphibians are not an exception (IUCN, 2018; Stuart, 2004). In fact, most clades are heavily threatened (Nori et al., 2015), and respond negatively (Nowakowski et al., 2017) to these activities. Considering that land-use changes are unevenly distributed across the globe and are strongly related with landscape characteristic and climatic regimes, it is expected that human modifications in the environment will affect differently anurans microhabitat-related ecomorphs. These idiosyncratic responses, coupled with a low performance of PAs (Jones et al., 2018; Watson et al., 2014) could constrained diversity of functional forms.

Here, using detailed geographical information on distribution pattern of 3138 amphibian species (categorized into seven ecomorphs), combined with land-use scenarios, for both current and future periods, we aim to: (1) describe the general patterns of species richness for amphibian ecomorphs; (2) analyze the overlap between patterns of amphibian ecomorph richness and different modified scenarios (3) estimate the role of the current global network of PAs in the long-term protection of the ecomorphs across the amphibian distribution; and (4) determine key regions to maximize amphibian life forms representation. Through these analyses we aim to provide new evidences about priority conservation areas for amphibians in a functional sense, taking into account global species patterns and different biological diversity aspects, that can guide futures conservation decision-making processes and the establishment of efficient areas for the long-term protection of amphibian.