Species–area relationship of Neotropical waterbird assemblages in remnant wetlands: looking at the mechanisms

Abstract

Aim We investigated the relative role of area, isolation, microhabitat diversity and number of individuals as explanatory factors defining the richness of waterbirds in wetland remnants.Location Freshwater marshes along the Atlantic coastal zone of South Brazil. (30°56′–30°22′S; 50°58–50°22′W; Fig. 1).The study area (dashed line), in the Atlantic coastal zone of Brazil, is characterized by a high concentration of remnant wetlands used by resident and migratory waterbirds. Waterbirds were surveyed monthly along 2003 in 42 randomly selected wetland remnants.imageMethods We surveyed waterbirds monthly for 1 year in 42 wetland remnants. We measured area, diversity of microhabitats, and isolation using aerial photographs and Landsat images. We compared the fit of the relationship between waterbird richness and wetland area across three models. We evaluated the ‘passive sampling effect’ comparing the observed species–area relationship with area‐based and individual‐based null models, performed with randomization without replacement. We used Path Analysis to measure the relative importance of direct and indirect effects of wetland area, isolation, microhabitat diversity and the total number of individuals on species richness.Results Power functions showed that larger wetlands had proportionally fewer species, individuals and microhabitats as compared to smaller wetlands. Species richness was consistently lower than predicted by area‐based and individual‐based random placement null models. Path analysis showed significant direct effects of remnant area and microhabitat diversity on species richness, but no effect of isolation on species richness. When number of individuals was included in the model, it became the most important factor explaining species richness, followed by wetland area. The number of individuals was significantly influenced by area, isolation and microhabitat diversity.Main conclusions We demonstrated that waterbird richness in fragmented landscapes is not a random placement phenomenon, but a biological one, significantly affected by the complex interplay of remnant area and isolation and diversity of microhabitats. We showed that the number of individuals plays a central role mediating the effect of these physical factors on species richness.

Estimating species – area relationships by modeling abundance and frequency subject to incomplete sampling

“…3C), suggesting that for these species small patches have the same value per unit area as large patches. However, for birds, our data focused on early-successional species in small plantation patches (<10 ha), so it is not surprising that bird species showed no area dependence of densities unlike studies on birds that covered a wider range of patch areas (Guadagnin et al 2009;Bidwell et al 2014;Dorazio and Connor 2014). On the other hand, we found that mature forest plant species as a group showed slightly higher occurrence probabilities in small patches (Fig.…”

“…However, for birds, our data focused on early‐successional species in small plantation patches (<10 ha), so it is not surprising that bird species showed no area dependence of densities unlike studies on birds that covered a wider range of patch areas (Guadagnin et al. ; Bidwell et al. ; Dorazio and Connor ).…”

Seasonal differences in drivers of species richness of waders in inland wetlands of La Mancha Húmeda Biosphere Reserve

“…Similarly, pond size was the factor most related to species richness in spring in a group of experimental ponds in Doñana (Sebastián‐González & Green, ). Guadagnin et al () also detected a positive relationship between wetland area and waterbird species richness over a year, partly owing to increased microhabitat diversity and individuals in large wetlands. The effect of increased area on waterbird richness is widespread (Brown & Dinsmore, ; Rosselli & Stiles, ), so it is surprising that in the present study it was only detected in winter.…”

Environmental and anthropogenic factors structuring waterbird habitats of tropical coastal lagoons: Implications for management

“…For example, Guadagnin et al (2009) found that waterbird abundance decreased with increasing area of fragmented wetlands in South Brazil. This finding was attributed to the low abundance of the larger species (e.g.…”