Stéphanie Gascón

Patterns of composition and species richness of crustaceans and aquatic insects along environmental gradients in Mediterranean water bodies

Differences in the dynamics of ecological processes between Mediterranean and colder temperate aquatic systems could imply different patterns in faunal communities in terms of composition and biodiversity (i.e. species richness and rarity). In order to identify some of these patterns the crustacean and aquatic insect composition and biodiversity of four water body types, classified according to their salinity and water permanence, were compared. Moreover, the relationships between species richness and water, pond and landscape variables were analysed. A total number of 91 water bodies located throughout Catalunya (NE Iberian Peninsula) were sampled. Three species assemblages were observed: one for permanent freshwaters, another for temporary freshwaters, and a third one for saline waters (SW), since permanent and temporary saline water bodies had similar composition. Differences in salinity were associated with proportion of crustaceans versus insects and with singularity. Thus, saline ponds had a higher proportion of crustaceans, and lower values of singularity. Conductivity was significantly related to total (crustaceans plus insects) richness, and also related to insect richness. The main difference between the models obtained for crustacean species richness and insect species richness is the significance of landscape variables in the latter, and this fact could be related to the different dispersion types of these two faunal groups: active for insects versus passive for crustaceans.

Spatial and temporal patterns of pioneer macrofauna in recently created ponds: taxonomic and functional approaches

Man-made ponds are often created to compensate for the loss and degradation of wetlands, but little is known about the processes taking place in these artificial environments, especially at a community level. The macrofaunal assemblage and water chemistry of newly created ponds in three nearby areas in the NE Iberian Peninsula were studied during the first year of life of these ponds in order to (i) detect if any invertebrate assemblage structure change was taking place, (ii) evaluate the effect of local factors on the invertebrate assemblage in each site, and (iii) compare the information obtained by taxonomic and functional approaches. Although invertebrate colonization was rapid, no relevant changes in assemblage parameters were related to time, implying that more time may be needed to detect successional changes in invertebrate assemblages. Local factors—especially those related to hydrological stability—produced notable differences both in the assemblage parameters and in the taxonomic and functional compositions of the invertebrate fauna. Finally, information provided by the functional approach was redundant with respect to that obtained by the classical taxonomic approach: in these newly created systems, the high dominance of a small number of taxa makes the functional approach a simple biological traits analysis of the few dominant species.

Identifying key environmental factors related to plant and crustacean assemblages in Mediterranean temporary ponds

The current interest in Mediterranean temporary wet habitats, considered to be habitats of European Community Interest, is mainly due to their characteristic flora and fauna. Several contributions characterize each of these two components separately, but considering them simultaneously could reveal possible interactions and a more complete view of the habitat that would be useful to improve conservation measures. This paper investigates crustacean and plant assemblages in six Mediterranean temporary ponds and their relationship with several environmental variables. Significant positive relationships were found between species richness and Shannon diversity index of plant and crustacean assemblages. Crustaceans had a higher similarity among ponds than plants and, consequently, each pond had a more characteristic assemblage of plants than of crustaceans. The two groups showed a different sensitivity to environmental factors and only two factors affected both: altitude and surface area of the wet system. Disturbances (e.g. grazing by cattle) and pond size were very important for plants, whereas they were irrelevant for crustaceans. On the other hand, distance to the nearest pond, hydroperiod length, and water nitrogen were only important for crustaceans. Although similar trends on richness and diversity were observed for both biotic groups, the use of only one of them for conservation programs would not be sufficient. Our results suggest that simultaneously taking into account several community components would result in a better understanding of ecosystem functionality.

Environmental filtering determines community patterns in temporary wetlands: A multi-taxon approach

Climate characteristics appear to play a key role in filtering organisms based on their biological traits. If this trait filtering by climate indeed occurs, it should have effects on the composition, dynamics, taxonomic relatedness and co-occurrence patterns of local assemblages, regardless of the taxonomic group considered. This preliminary study aimed to assess the extent to which environmental variables might determine these patterns in local communities and to evaluate whether the ultimate cross-taxon congruence relationships are consistent across, or dependent on, the selected region. To this end, we studied the bryophyte, macrophyte, macroinvertebrate, and amphibian communities in two clusters of temporary wetlands on the NE Iberian Peninsula under mesothermal and semiarid climates. We observed effects of environmental filtering, with the communities differing between the climatic regions not only in their compositions but also in their dynamics and taxonomic relatedness patterns. Although the cross-taxon congruence in terms of species richness was high in the mesothermal climate, most of the congruent relationships were disrupted in the semiarid environment. Overall, because climate-dependent patterns appear to prevail over climate-consistent ones, we suggest that the use of surrogate taxa may be of limited value when aiming to assess wetland biodiversity across large areas.

Comparative biodiversity of crustaceans and aquatic insects from various water body types in coastal Mediterranean wetlands

Coastal wetlands are characterized by a high biodiversity. At the same time, biodiversity is one of the main criteria used to establish protection policy priorities, or to propose management actions. In this study, crustacean and aquatic insect species richness in the Emporda wetlands was investigated. These two groups contribute in an important way to the total biodiversity, and still they are seldom taken into account in the management of natural areas. Representative samples (38 points) of all aquatic water body types in the Emporda wetlands were taken monthly (dip net with 250 μm mesh). Sampling was carried out between 1996 and 2000, but until present, only qualitative data have been extracted. A rich fauna of 125 crustacean taxa and 295 aquatic insect taxa were found. Some environments were characterized by low richness and high singularity (isolated artesian freshwater springs), some by high richness and high singularity (estuarine waters, brackish and meso-eutrophic freshwater wetlands), and others by low richness and low singularity (hypertrophic freshwater wetlands and hyperhaline wetlands). Factors determining singularity and richness are discussed. Comparison with crustacean richness of other western Mediterranean wetlands showed a similar high species richness in our study sites, probably due to high spatial heterogeneity of these areas.

Functional and Phylogenetic Relatedness in Temporary Wetland Invertebrates: Current Macroecological Patterns and Implications for Future Climatic Change Scenarios

In freshwater ecosystems, species compositions are known to be determined hierarchically by large to small‑scale environmental factors, based on the biological traits of the organisms. However, in ephemeral habitats this heuristic framework remains largely untested. Although temporary wetland faunas are constrained by a local filter (i.e., desiccation), we propose its magnitude may still depend on large-scale climate characteristics. If this is true, climate should be related to the degree of functional and taxonomic relatedness of invertebrate communities inhabiting seasonal wetlands. We tested this hypothesis in two ways. First, based on 52 biological traits for invertebrates, we conducted a case study to explore functional trends among temperate seasonal wetlands differing in the harshness (i.e., dryness) of their dry season. After finding evidence of trait filtering, we addressed whether it could be generalized across a broader climatic scale. To this end, a meta-analysis (225 seasonal wetlands spread across broad climatic categories: Arid, Temperate, and Cold) allowed us to identify whether an equivalent climate-dependent pattern of trait richness was consistent between the Nearctic and the Western Palearctic. Functional overlap of invertebrates increased from mild (i.e., Temperate) to harsher climates (i.e., Arid and Cold), and phylogenetic clustering (using taxonomy as a surrogate) was highest in Arid and lowest in Temperate wetlands. We show that, (i) as has been described in streams, higher relatedness than would be expected by chance is generally observed in seasonal wetland invertebrate communities; and (ii) this relatedness is not constant but climate-dependent, with the climate under which a given seasonal wetland is located determining the functional overlap and the phylogenetic clustering of the community. Finally, using a space-for-time substitution approach we suggest our results may anticipate how the invertebrate biodiversity embedded in these vulnerable and often overlooked ecosystems will be affected by long-term climate change.

Modelling the response of floodplain aquatic assemblages across the lateral hydrological connectivity gradient

Hydrological connectivity is one of the main controlling factors of habitats and aquatic assemblages on river floodplains. Nevertheless, the lack of universal measures of river–floodplain connectivity (i.e. the lateral hydrological connectivity, LHC) limits the comparison of the response of aquatic assemblages to hydrological connectivity and impedes the understanding of floodplain functioning across different systems. To address these needs, we tested the ability of six different LHC surrogates to model changes in richness, abundance and composition of aquatic assemblages across a Mediterranean floodplain (Ebro River, NE Spain). As shown by generalised additive models, LHC surrogates explained 15% to 65% of the richness and abundance of aquatic assemblages. Zooplankton, macroinvertebrates and phytoplankton showed overlapping peaks of richness at flood duration rates of 5, 15 and 30 days year–1 respectively. Redundancy analyses showed that LHC surrogates explained 17% to 37% of aquatic assemblage composition. Distance to the river and flood duration were the most important determinants of macroinvertebrate composition, whereas flood magnitude and water-level variability best accounted for the variance in zooplankton and phytoplankton compositions. Models based on LHC surrogates such as those presented here can help in predicting the consequences of restoration measures and may be useful in setting restoration goals for aquatic assemblages.

Change in biological traits and community structure of macroinvertebrates through primary succession in a man-made Swedish wetland

Abstract.  We investigated the successional development of a benthic macrofaunal community in Kalmar Dämme, a man-made wetland in southeastern Sweden, over a 13-y period after construction (1997–2009). We assessed primary succession by monitoring changes in species composition, biological traits, and community structure. Predictable successional changes occurred, and the structure of the community was complex at the advanced phase. Three successional phases were observed, each with typifying species. At the advanced phase, dominant biological traits shifted to favor animals with longer life-cycle durations, aerial dispersal strategies, and certain feeding types (i.e., filter-feeders, fine sediment collectors, predators, and parasites). We selected the Coleoptera assemblage to represent the macroinvertebrate community in an evaluation of the extent to which man-made wetlands in different age classes (<3 y and ≥10 y) were similar to natural wetlands (>50 y). No significant differences in Coleoptera assemblages were found between natural wetlands and man-made wetlands ≥10 y. However, man-made wetlands ≥10 y had significantly higher coleopteran species richness than natural and man-made wetlands <3 y because of the convergence of pioneering species persisting from early successional stages with representative specialized taxa from natural wetlands. Our results suggest that 10 y may be sufficient time for the macrofaunal communities of man-made wetlands to resemble those of natural wetlands.

Predation and competition effects on the size diversity of aquatic communities

Body size has been widely recognised as a key factor determining community structure in ecosystems. We analysed size diversity patterns of phytoplankton, zooplankton and fish assemblages in 13 data sets from freshwater and marine sites with the aim to assess whether there is a general trend in the effect of predation and resource competition on body size distribution across a wide range of aquatic ecosystems. We used size diversity as a measure of the shape of size distribution. Size diversity was computed based on the Shannon-Wiener diversity expression, adapted to a continuous variable, i.e. as body size. Our results show that greater predation pressure was associated with reduced size diversity of prey at all trophic levels. In contrast, competition effects depended on the trophic level considered. At upper trophic levels (zooplankton and fish), size distributions were more diverse when potential resource availability was low, suggesting that competitive interactions for resources promote diversification of aquatic communities by size. This pattern was not found for phytoplankton size distributions where size diversity mostly increased with low zooplankton grazing and increasing nutrient availability. Relationships we found were weak, indicating that predation and competition are not the only determinants of size distribution. Our results suggest that predation pressure leads to accumulation of organisms in the less predated sizes, while resource competition tends to favour a wider size distribution.

Spatio-temporal variability of faunal and floral assemblages in Mediterranean temporary wetlands.

Six temporary wetlands in the region of Sejenane (Mogods, NW Tunisia) were studied in order to characterize the aquatic flora and fauna and to quantify their spatio-temporal variability. Samplings of aquatic fauna, phytosociological relevés, and measurements of the physicochemical parameters of water were taken during four different field visits carried out during the four seasons of the year (November 2009-July 2010). Despite the strong anthropic pressures on them, these temporary wetlands are home to rich and diversified biodiversity, including rare and endangered species. Spatial and temporal variations affect fauna and flora differently, as temporal variability influences the fauna rather more than the plants, which are relatively more dependent on spatial factors. These results demonstrate the interest of small water bodies for maintaining biodiversity at the regional level, and thus underscore the conservation issues of Mediterranean temporary wetlands that are declining on an ongoing basis currently.