Date Published: February 13, 2018
Publisher: Public Library of Science
Author(s): Francisco Ramírez, Carlos Rodríguez, Javier Seoane, Jordi Figuerola, Javier Bustamante, Bi-Song Yue.
Global warming and direct anthropogenic impacts, such as water extraction, largely affect water budgets in Mediterranean wetlands, thereby increasing wetland salinities and isolation, and decreasing water depths and hydroperiods (duration of the inundation period). These wetland features are key elements structuring waterbird communities. However, the ultimate and net consequences of these dynamic conditions on waterbird assemblages are largely unknown. We combined regular sampling of waterbird presence through one annual cycle with in-situ data on relevant environmental predictors of waterbird distribution to model habitat selection for 69 species in a typical Mediterranean wetland network in southwestern Spain. Species associations with environmental features were subsequently used to predict changes in habitat suitability for each species under three climate change scenarios (encompassing changes in environmental predictors that ranged from 10% to 50% change as predicted by regional climatic models). Waterbirds distributed themselves unevenly throughout environmental gradients and water salinity was the most important gradient structuring the distribution of the community. Environmental suitability for the guilds of diving birds and vegetation gleaners will decline in future climate scenarios, while many small wading birds will benefit from changing conditions. Resident species and those that breed in this wetland network will also be more negatively impacted than those using this area for wintering or stopover. We provide a tool that can be used in a horizon-scanning framework to identify emerging issues in waterbird conservation and to anticipate suitable management actions.
Wetlands have some of the highest biodiversity and biological productivity levels in the world [1,2], and several globally threatened species largely depend on them [1,3,4]. Although many of the world’s most important wetlands are protected, they are also affected by a range of human and climate-driven impacts that may threaten their biodiversity and associated ecosystem services [2,5–8]. For instance, human activities have resulted in extensive wetland fragmentation, modification and loss [4,9–12]. The impact on wetlands has been exacerbated by the natural insularity of these patchy habitats, which are surrounded by a terrestrial matrix [13,14]. Ultimately, this has resulted in biodiversity loss rates that far exceed those of other, more terrestrial ecosystems [1,6,15].
The environmental features that best explain waterbird presence at the point-count were water salinity, water depth, waterbody isolation and hydroperiod duration (Table 3). In turn, these variables were also those most likely to be affected by climate-driven changes in water budgets. However, the GAM estimated coefficients and the BRT relative importance for these key environmental predictors clearly differed among waterbird species and guilds (see S1 and S2 Tables). Overall, water salinity was highlighted as the main environmental predictor for the whole waterbird assemblage regardless of the statistical procedure considered (i.e., GAMs or BRTs; see Table 3, Fig 4 and S1 and S2 Tables). Fishing birds and small wading birds were clearly associated with the highest salinities (tidal areas and salt pans). In contrast, vegetation gleaners and diving birds preferentially used permanent (longer hydroperiods) and deep waterbodies with the lowest salinities (fresh water). Large wading birds inhabit preferentially shallow and permanent waterbodies with a large range of salinities, whereas dabbling ducks mainly occurred in deep but ephemeral waterbodies with intermediate salinities. Finally, raptor distributions were mainly influenced by waterbody isolation. These results were consistent with those obtained from the independent dataset (see S1 File).
Prospective exercises aimed at horizon-scanning human and climate impacts on waterbirds require a thorough comprehension of the environmental drivers structuring their habitats [23,33]. By investigating waterbird distribution in a wetland network in southwestern Spain, we identified a comprehensive set of environmental predictors of habitat use. In particular, several water budget-related environmental traits such as salinity, water depth, water body isolation and hydroperiod, structured the community and were revealed as the most important habitat features predicting species presence. However, various species and guilds showed specific and contrasting responses to different environmental predictors. Accordingly, we should expect that the impact of human and climatic-driven changes in water budgets on waterbirds will be species and guild-specific.