Environ Biol Fish DOI 10.1007/s10641-015-0450-0
Persistence and instability typify the fish assemblage structure of Rio Ubatiba, a Neotropical stream of South-east Brazil Javier Lobon-Cervia & Rosana Mazzoni & Ricardo Iglesias-Rios & Erica Pellegrini Caramaschi
Received: 29 September 2014 / Accepted: 28 August 2015 # Springer Science+Business Media Dordrecht 2015
Abstract The objective was to explore levels of persistence and stability of a Neotropical fish assemblage in a typical Serra do Mar stream (Southeast Brazil) over 1994–2008 with 90 quantitative samples in total. All along the stream gradient, the fish assemblage was composed of small-sized, short living species including benthic and water column species. Only four species occurred at the uppermost site (i.e., S1) whereas these four species plus eight species occurred at all other sites. In regards to species presence-absence, all species were temporally persistent at all sites over the study years. Overall, all species were abundant across scales of space and time with only three out of 14 species showing consistently low densities along the stream across years. Nevertheless, as indicated by the temporal variations in the Coefficients of Variation (CV%), the fish assemblages were highly unstable at all sites over time. At all sites the CV% varied widely and increased significantly over the years. No consistent density-dependence was elucidated nor any significant correlation among
J. Lobon-Cervia (*) National Museum of Natural Sciences (CSIC), C/José Gutiérrez Abascal, 2, Madrid 28006, Spain e-mail:
[email protected] R. Mazzoni Dept. de Ecologia, Lab. de Ecologia de Peixes, Universidade do Estado do Rio de Janeiro, IBRAG, Av. São Francisco Xavier, 524, Maracanã, Rio de Janeiro 20550-013, Brazil R. Iglesias-Rios : E. P. Caramaschi Inst. de Biologia, Dept. de Ecologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro CP 68020, Brazil
environmental variables and assemblage attributes were detected. The only consistent relationship elucidated relates the CV% of assemblage variability over time and the CV% of the ratio between stream discharge in the two major seasons, May and November. Keywords Neotropical stream . Fish assemblages . Density and structure . Persistence . Instability . Longterm
Introduction The structures of the fish assemblages are dynamic by nature. The identification of the factors and mechanisms underlying temporal fluctuations is central in community ecology (Lawton and Gaston 1989) and has motivated considerable interest among ecologists during recent decades (Matthews and Heins 1987; Gido and Jackson 2010). As an applied issue, environmentalists and fishery managers need to document levels of stability and persistence if they are to assess environmentally induced (i.e., climatic variability, global change and global warming scenarios, etc.) and/or human-induced alterations on assemblage dynamics and their habitats. Levels of assemblage variability (or otherwise, persistence and stability) are deemed to depend on the temporal variability of the habitats and on the interactions among assemblage members. The general assumption, as summarized by Grossman et al. (1998), is that, in the absence of predators, two primary suites of mechanisms regulate assemblage structures. On the one hand,
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where assemblages are subject to unpredictable environments, the co-existence among species is possible when environmental variations reduce their densities to levels under which resources limitations occur. In such unpredictable environments, assemblage members may overlap in resources use and temporally unstable structures would be a major assemblage attribute. Inherent to environmentally driven assemblages is that extinction risks increase when environmental variability persists on time (Inchausti and Halley 2003). At the opposite extreme, in habitats where resources limitations occur frequently, assemblage members tend to reduce overlapping in resources use; their temporal variations concur with changes in resources availability and their structures would persist over time despite great environmental variability. Thus, the role of species interactions on assemblage structure depends tightly on temporal stability. If assemblages are not persistent over time and/or show no resilience mechanisms then, it is most unlikely that interactive segregation is the dominant factor driving assemblage structures. A major problem in testing assemblage structurerelated hypotheses is the need for long-term studies. Despite a shortage of such data and the apparent difficulty to characterize temporal variability (Grossman et al. 1990), several studies have assessed relationships among environmental variability, resources partitioning and the structure, diversity and stability of stream fish assemblages (Grossman et al. 1998; Schaefer et al. 2012). “A priori”, the relative importance of species interactions versus environmental variability may differ among assemblages composed of phylo-genetically and eco-morphologically divergent species and/or among streams differing in geology, geomorphology and climatic conditions and their concurrent variations in primary and secondary production. This notion stems from the discrepancies in the results reported in the literature. For example, some fish assemblages may change dramatically in composition and abundance over short time scales as a response to severe discharge variations such as floods (Matthews 1986) and droughts (Matthews and Marsh-Matthews 2003) whereas similar environmental stressors have no obvious effect on other fish assemblages (Lobón-Cerviá 1996). For fish assemblages in US streams, Moyle and Vondracek (1985) described high levels of stability whereas Matthews et al. (1988) compared temporal stability over a gradient of benignto-harsh conditions and concluded that assemblage structures were more stable in environmentally benign
streams than in those subject to greater environmental variability. Nevertheless, recent observational (Poff and Allan 1995; Snelder and Lamoroux 2009) and experimental studies (Matthews and Marsh-Matthews 2006) have emphasized the importance of environmental variability. These studies highlighted a major role of hydrological factors as drivers of assemblages structure and minimized the relative importance of resource limitations and interactive segregation (Matthews and MarshMatthews 2006). Although evidence for the occurrence of environmental drivers is steadily accumulating, there is still no consensus over the relative importance of each suite of factors and/or under what conditions each suite of factor predominate across fish assemblages, streams and geographical/climatic regions. Importantly, vast zoogeographical regions as the Neotropics where streams fish diversity is recognized to be the largest worldwide (Mojica et al. 2009) and where pristine streams are still abundant, have received little attention (Medeiros and Maltchik 2001). Studies on the Neotropical Frontier may not only provide deeper insight into the conditions under which comparable factors and mechanisms drive assemblages structure composed of phylo-genetically and morphologically divergent species across geographical regions. The objective of this study, based on a unique longterm monitoring procedure, was to explore levels of persistence and stability of a fish assemblage across scales of space (i.e., a network of sites along the environmental gradient of Rio Ubatiba, a typical Serra do Mar stream, Rio de Janeiro, South-east Brazil) and time (i.e., over 12 years). We further explored relationships among levels of stability, density-dependence and environmental factors. As aforementioned, to elucidate the role of species interactions on assemblage structure depends tightly on the temporal stability as the relative constancy in species abundance over time (Meffe and Minckley 1987) that may only result from resistance to environmental disturbance or to the resilience of the assemblage, the ability to return to the original state after the effects of the disturbance. We explored two alternative hypotheses: Firstly, we tested a density-dependent hypothesis related to temporal variations in the rates of numerical change of assemblage members (Dennis and Taper 1994), under the assumption that if these rates describe consistently positive trends over time then, species interactions will predominate independently of the environmental variations. Secondly, we tested the
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“more time, more variability hypothesis” (Bengtsson et al. 1997) under the assumption that if variability in the assemblages structure increases over time (and synchronously across sites over the stream gradient) then, environmental variability but not species interactions, might be the major mechanisms driving assemblages structure.
Study area, material and methods The Rio Ubatiba The Rio Ubatiba is a transparent waters, 20 km long stream (66 % of the instances, the estimated number of individuals with ≥ six removals were well above the 95 % Confidence limits (i.e., 95 % CL) of the estimates obtained with only two removals. However, in a remarkably high 83 % of the instances, those numbers estimated with ≥6 removals were within the 95 % Confidence Intervals of those estimates obtained with three removals that in turn, showed much more conservative variances. Consequently, after the second year, we reduced the fishing efforts to only three removals that were applied in all other density estimates upon which we tested for the homogeneity of the catch ability (i.e., a measure of fishing efficiency) over successive removals (Lobón-Cerviá 1991; Mazzoni and Lobón-Cerviá 2000). After sampling, we drew bathymetric maps of each site and date to quantify in-stream characteristics
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(species presence-absence) across scales of space and time. We then examined levels of stability (as defined above) of the fish assemblage in May and November over the years. Several studies have used Kendall W to quantify temporal stability s (i.e., Matthews et al. 1988). However, Grossman et al. (1990) suggested several advantages of the Coefficients of Variation (CV%=100 * Standard Deviation / Mean) over Kendall W. We followed these authors to quantify levels of stability and applied their classification scheme where values of CV%
