Elsevier

Estuarine, Coastal and Shelf Science

Volume 196, 5 September 2017, Pages 134-140
Estuarine, Coastal and Shelf Science

Geographic variation in species richness, rarity, and the selection of areas for conservation: An integrative approach with Brazilian estuarine fishes

https://doi.org/10.1016/j.ecss.2017.06.022Get rights and content

Highlights

  • Species richness, endemism and rarity of Brazilian estuarine fishes were mapped.

  • Areas of high conservation value were identified.

  • Rio de Janeiro, Bahia and the Amazonian coast emerged as priority for protection.

  • Most priority areas for conservation are currently unprotected.

Abstract

While the number of species is a key indicator of ecological assemblages, spatial conservation priorities solely identified from species richness are not necessarily efficient to protect other important biological assets. Hence, the results of spatial prioritization analysis would be greatly enhanced if richness were used in association to complementary biodiversity measures. In this study, geographic patterns in estuarine fish species rarity (i.e. the average range size in the study area), endemism and richness, were mapped and integrated to identify regions important for biodiversity conservation along the Brazilian coast. Furthermore, we analyzed the effectiveness of the national system of protected areas to represent these regions. Analyses were performed on presence/absence data of 412 fish species in 0.25° latitudinal bands covering the entire Brazilian biogeographical province. Species richness, rarity and endemism patterns differed and strongly reflected biogeographical limits and regions. However, among the existing 154 latitudinal bands, 48 were recognized as conservation priorities by concomitantly harboring high estuarine fish species richness and assemblages of geographically rare species. Priority areas identified for all estuarine fish species largely differed from those identified for Brazilian endemics. Moreover, there was no significant correlation between the different aspects of the fish assemblages considered (i.e. species richness, endemism or rarity), suggesting that designating reserves based on a single variable may lead to large gaps in the overall protection of biodiversity. Our results further revealed that the existing system of protected areas is insufficient for representing the priority bands we identified. This highlights the urgent need for expanding the national network of protected areas to maintain estuarine ecosystems with high conservation value.

Introduction

Spatial conservation strategies are often based on geographic patterns of biodiversity (Roberts et al., 2002, Brooks et al., 2006). To be effective, such strategies require spatially accurate and representative information on the distribution of biota. The lack of detailed data on geographic distribution of most biological groups, however, has not only hindered the application of methods for setting conservation priorities, but also constrained our ability to understand patterns in biodiversity. Obtaining a comprehensive measure of the spatial patterns of biodiversity is also hampered by the complexity of the concept (Purvis and Hector, 2000). For these reasons, conservation prioritization exercises often focus on univariate metrics, such as the number of species, to guide protection and restoration efforts (Brooks et al., 2006, Allen, 2008, Trebilco et al., 2011).

The total number of species (hereafter species richness) is a relatively simple and easy measure of an area's relevance to conserve biodiversity. There is solid evidence that species-rich places have increased ability to maintain key ecosystem services (e.g. food production, water quality maintenance, etc.), to recover from disturbances and to resist to invasions (Worm et al., 2006). The local species richness, however, is only one among many attributes of biodiversity. This means that choosing areas for protection on the basis of only species richness may be inadequate to represent, for example, small-ranged and endemic species, which often have idiosyncratic geographical distributions and a high propensity to become locally rare or extinct (Roberts et al., 2002, Orme et al., 2005). Because of this, the value of spatial conservation strategies is enhanced when measures of richness are associated with complementary biodiversity metrics, such as rarity and endemism (Fleishman et al., 2006).

Using the Mexican avifauna and South American anurans as models, Villalobos et al., 2013a, Villalobos et al., 2013b proposed a straightforward approach to define conservation priorities at large spatial scales integrating both richness and rarity. Species considered rare because of their restricted geographic ranges also tend to have relatively small populations – two attributes that make them more prone to extinction (Roberts and Hawkins, 1999). Hence, rarity per se has been considered a double jeopardy (Gaston, 1998). Rare species often have traits distinct from those of common species and are responsible for essential – and vulnerable – ecological functions in assemblage structuring and ecosystem functioning (Mouillot et al., 2013). Conservation efforts directed to locally rare species are important even if they are common elsewhere, because they can prevent the loss of essential parts for the functioning of local ecosystems, of genetic diversity and, ultimately, extinction events (Hunter and Hutchinson, 1994, Mouillot et al., 2013).

In this study, the geographic patterns of species richness and rarity of the estuarine fish fauna were mapped and integrated to identify regions of potential conservation value on the Brazilian coast (which encompasses the whole Brazilian Province, sensu Floeter et al., 2008). We also analyzed the effectiveness of the existing system of protected areas to represent these regions. The main goal was to investigate the following questions: (1) what are the most species-rich areas for estuarine fishes? (2) where are concentrated the estuarine fish species rarer in Brazil? (3) which areas have both high estuarine fishes richness and species with relatively small geographical ranges? (4) to what extent the existing protected areas cover these crucial regions and how one might make improvements? A secondary goal was to test whether different measures of biodiversity (species richness, endemism and rarity) are spatially congruent and efficient as surrogates for each other.

Section snippets

Database

A list of estuarine fish species in Brazil was compiled from (1) studies conducted in 31 estuaries distributed along the whole coast; (2) regional checklists, identification guides, and scientific collections (references in Appendix A1). Data collection was restricted to environments that, even loosely, meet the definition of estuary proposed by Day (1980), i.e., any “partially enclosed coastal body of water which is either permanently or periodically open to the sea and within which there is a

Results

Of the 412 estuarine fish species considered, 371 are Actinopterygii and 41 Elasmobranchii. The total number of species per latitudinal band ranged from 160 to 328 (mean ± SD = 281 ± 52 species). The species-richest bands are situated on the coast of the state of Rio de Janeiro, where 79.6% of all fish species included in this study are estimated to occur in a single band. The coast of Rio Grande do Sul (in temperate latitudes) has the lowest total richness (Fig. 2a). The number of endemic

Discussion

For the first time are described and elucidated the interrelationship between the geographic patterns of species richness, endemism and rarity of estuarine fish fauna along the Brazilian coast. Our results revealed that (1) centers of species richness and endemism of estuarine ichthyofauna are geographically incongruent; (2) the spatial pattern of rarity for all species is remarkably different from that found for endemic species; (3) the metrics analyzed (species richness, endemism and rarity)

Acknowledgements

This study is dedicated to Rogério L. Teixeira (in memoriam) for his vast legacy on the Brazilian biodiversity and for encouraging several researchers to take their first steps in Science. We are grateful to Maurício Noemberg (Universidade Federal do Paraná) for building the latitudinal bands and to the anonymous reviewers for their valuable comments. C.C.V. also thanks CAPES for financial support during the writing of this manuscript.

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