Dissimilarity in plant species diversity between salt marsh and neighboring environments decreases as environmental harshness increases

Abstract

How species similarity changes between habitats along environmental gradients is still a central challenge in ecological studies. We assessed whether marsh plant characteristics are associated with geographic changes in environmental conditions and whether there are environmental factors associated with marsh−inland dissimilarity in species composition. Field samples of vegetation were collected at 6 sites along the SW Atlantic to determine plant characteristics (cover, tallness, richness and α-diversity), and marsh-inland dissimilarity (β-diversity) in species composition was calculated. PERMANOVA analysis showed that plant assemblage changes among sites. Forward stepwise multiple regression analysis showed that in lower marsh, plant cover increased in association with tidal range and decreased in association with salinity. In the high marsh, plant cover decreased in association with tidal range, salinity and with minimum temperatures. Plant richness increased in association with tidal range and with marsh area, while α-diversity decreased in association with precipitation and increased with salinity. Beta-diversity, estimated by SIMPER analysis, increased in association with precipitation and decreased with salinity and daily thermal amplitude. We present evidence that there is an increase in α-diversity but a decrease in β-diversity with environmental severity among co-specific marshes distributed along the SW Atlantic coast. Thus, communities developing in more benign conditions, regardless of their low local diversity, may increase biodiversity at a landscape scale by decreasing their similarities.

Small Mammals Along SW-Atlantic Marshes: Diversity Correlates with Inland Habitats but Abundance Correlates with Marsh Characteristics

“…The northern marshes (SC and MCH) are surrounded by the Pampas grasslands Biogeographic Province, characterized by herbaceous stratus which is dominated by the silver pampas grass Cortaderia selloana and the spiny rush Juncus acutus. These marshes are characterized by higher precipitation (SC=950 mm year −1 , MCH=920 mm year −1 , Canepuccia et al 2013) than southern marshes and are subject to freshwater input from La Plata River estuary (caudal around 22,000 m 3 s −1 ). Marshes in the middle portion of our study area received intermediate levels of precipitation (BB=645 mm year −1 , BA=500 mm year −1 Canepuccia et al 2013), while the southernmost marsh received the lowest level of precipitation (BSA = 248 mm year −1 , Canepuccia et al 2013).…”

“…These marshes are characterized by higher precipitation (SC=950 mm year −1 , MCH=920 mm year −1 , Canepuccia et al 2013) than southern marshes and are subject to freshwater input from La Plata River estuary (caudal around 22,000 m 3 s −1 ). Marshes in the middle portion of our study area received intermediate levels of precipitation (BB=645 mm year −1 , BA=500 mm year −1 Canepuccia et al 2013), while the southernmost marsh received the lowest level of precipitation (BSA = 248 mm year −1 , Canepuccia et al 2013). BB, BA and BSA marshes were adjacent to Monte Biogeographic Province on the landward side ( Fig.…”

“…In addition, the precipitation gradient may also influence the type of inland habitat that surrounds the Spartina marshes (Cabrera and Willink 1973). Consequently, these Spartina marshes may be adjacent to different inland habitats (Canepuccia et al 2013; see Fig. 1).…”

“…1). These Spartina marshes are distributed along a gradient of precipitation, decreasing from 1,200 mm in the north to 200 mm in the south (Isacch et al 2006;Canepuccia et al 2013). This gradient of precipitation may affect the abundance and distribution of small mammals (Stenseth et al 2002;Canepuccia et al 2008b;Canepuccia et al 2010) by driving changes in salinity stress in marsh sediment and marsh vegetation structure (Canepuccia et al 2010).…”

“…The northern marshes are limited by Pampa grassland, which is dominated by a grass steppe. Marshes located in the south are surrounded by different species of shrubs and halophytic grasses which are characteristic of the Monte landscape (Canepuccia et al 2013 habitat types, which may affect the abundance and composition of small mammals in marshes.…”