Final Report Summary - CLITEMP (Climate change effects on aquatic and terrestrial invertebrate assemblages in European rivers: the influence of duration of dry period in temporary rivers)
The general objective of the CLITEMP project was to investigate how the duration, extent and severity of the dry period control both aquatic and terrestrial assemblages; as a basis to forecast the potential effects of climate change on Mediterranean river biodiversity and ecosystem processes.
The specific objectives were: 1) to analyse changes in community structure and composition and biological traits of macroinvertebrate assemblages along a gradient of flow intermittence in temporary rivers, 2) to investigate the effect of the duration of the dry period on terrestrial invertebrate assemblages and the trophic linkages between aquatic and terrestrial assemblages, and 3) to investigate the role of temporary rivers as corridors for terrestrial animals during the dry period.
CLITEMP has produced research results of high quality, presented its outcome at major international conferences, and is in the process of publishing the results in high impact journals.
-Influence of flow intermittence and duration of flow period on aquatic invertebrate communities
To approach this first objective, aquatic invertebrate communities were studied along a gradient of flow intermittence in temporary streams undergoing different drying patterns (two different climate types in Europe: arid and temperate). The main results were:
•Flow intermittence (corresponding to the cease of surface flow) had significant effects on community structure and composition as well as on biological traits of benthic invertebrates. Total richness, EPT richness (Ephemeroptera, Plecoptera and Trichoptera), and EPT abundance were significantly higher in perennial than in intermittent reaches (both studied streams). In addition, the biological traits related to dissemination mode, resistant form, and feeding habit were most affected by flow intermittence.
•Both the duration of the dry period and the distance to the nearest perennial reach affected community structure and the related biological traits. Total richness and EPT richness decreased with both increasing duration of the dry period and distance to perennial reaches. Furthermore, the abundance of aerial active taxa increased with both increasing duration of dry period and distance to perennial reaches (both streams).
•Invertebrate assemblages at the most intermittent sites were nested subsets of assemblages at the least temporary and perennial sites (both streams).
In conclusion, our findings support the hypothesis that flow intermittence is a master variable driving river assemblage structure and composition and biological trait distribution (as evidenced from two rivers studied, which belong to different climate types). When flow intermittence increased (quantified as the duration of the dry period and the distance to perennial reaches), taxonomic richness of invertebrate assemblages decreased. In addition, assemblage nestedness most likely resulted from both limited dispersal from source communities of perennial reaches and local extinction due to increasing flow intermittence.
These findings have an important impact on research, management, and monitoring of temporary streams and rivers in the context of climate change; with direct implications for the bioassessment of temporary streams in the context of the European Water Framework Directive. These findings will help to water managers to reformulate current bioassessment and monitoring schemes of temporary river basins, where the effect of flow intermittence on aquatic invertebrate communities has been generally neglected so far.
-Effects of flow intermittence on ground-dwelling arthropod assemblages in channels and fringing terrestrial habitats of temporary streams.
To approach this second objective, terrestrial invertebrate communities were quantitatively collected in temporary streams and the adjacent terrestrial habitats (riparian and upland areas). The main results were:
• Flow intermittence and the duration of the dry period strongly influenced terrestrial arthropod assemblages, not only in the stream channel but also in the adjacent terrestrial habitats (riparian and upland areas).
• The composition of arthropod assemblages differed between flow regime types (perennial and intermittent types), habitat types (channel, riparian and upland areas), and sampling dates (a during a 1-month dry phase). In contrast, taxonomic richness and total abundance were similar between perennial and intermittent reaches, but differed among habitat types, depending on the studied temporary stream.
•In one of the studied streams arthropod abundances peaked in the dry channel and increased with drying time; at the same time abundances decreased in riparian and upland habitats.
In conclusion, the results emphasize the importance of dry channels in temporary rivers as temporal habitats for terrestrial arthropod assemblage and provide evidence that the dry channel may be colonized by both riparian and upland arthropods. Our findings advance the notion that special attention need to be paid to the duration of the dry period, given the concomitant change in the composition and the structure terrestrial arthropods undergo with time.
The findings have a relevant impact on the research and management of temporary rivers, especially in relation to the bioassessment of temporary rivers during the dry phase. Metrics based on terrestrial arthropods may reflect the ecological status of intermittent streams during the dry phase, and therefore should complement existing monitoring strategies that only focus on aquatic organisms. Temporary streams are coupled aquatic and terrestrial ecosystems, and both states need to be adequately considered when understanding and managing them.
-Temporary rivers as corridors for terrestrial fauna during the dry period.
To approach this third objective, a review and conceptual work about the function of corridors for both aquatic and terrestrial animals was conducted (manuscript close to submission). In addition, a field study testing the use of dry river beds by terrestrial vertebrates was performed in two temporary streams. The main results related to the first approach (review and conceptual paper) were:
• Rivers are generally perceived as corridors for aquatic animals embedded in a terrestrial landscape. The presence of IRs in river networks changes this view of river corridors.
• Intermittent rivers are coupled aquatic-terrestrial corridors. In IRs, the alternation of wet and dry periods creates a mosaic of aquatic and terrestrial habitats. IRs are not only suitable pathways for the movement of aquatic species during wet conditions (aquatic corridor), but also for terrestrial species during dry periods (terrestrial corridor).
• Flow intermittence influences the movement of animals in temporary rivers and therefore has major ecological consequences. The movement of aquatic species in temporary rivers is naturally limited during the dry phase (except for flying species, aerial stages of insects, passive wind dispersers). Dry river beds increase the connectivity between patches along river networks and may serve as preferential pathways for terrestrial animals.
Main results related to the second approach were:
•Dry beds were widely used by vertebrates (mammals, reptiles and birds), especially along vegetated stream sections.
•The use of the different habitat types (dry river bed, riparian, upland, and unpaved road) was consistent among vertebrate groups.
•In dry beds, directional tracks were more frequent than non-directional ones, with a prevalence of tracks running parallel to the river line; particularly in summer.
In conclusion, our findings support the idea that temporary rivers act as corridors for terrestrial vertebrates. River beds might be particularly important for long-distance movements along the river course, in contrast to perpendicular movements (i.e. crossings). Finally, the permeability of the surrounding landscape can be a key factor that influences the use of temporary rivers as dispersal and migration corridors.
The findings have strong implication in the management of temporary rivers as landscape corridors. We provide evidence that dry river beds are ecological corridors that increase natural connectivity between patches (e.g. water holes, other suitable habitats). Temporary rivers are both terrestrial and aquatic corridors along entire river networks and, therefore, should be considered and managed within the context of blue and green infrastructures.
The specific objectives were: 1) to analyse changes in community structure and composition and biological traits of macroinvertebrate assemblages along a gradient of flow intermittence in temporary rivers, 2) to investigate the effect of the duration of the dry period on terrestrial invertebrate assemblages and the trophic linkages between aquatic and terrestrial assemblages, and 3) to investigate the role of temporary rivers as corridors for terrestrial animals during the dry period.
CLITEMP has produced research results of high quality, presented its outcome at major international conferences, and is in the process of publishing the results in high impact journals.
-Influence of flow intermittence and duration of flow period on aquatic invertebrate communities
To approach this first objective, aquatic invertebrate communities were studied along a gradient of flow intermittence in temporary streams undergoing different drying patterns (two different climate types in Europe: arid and temperate). The main results were:
•Flow intermittence (corresponding to the cease of surface flow) had significant effects on community structure and composition as well as on biological traits of benthic invertebrates. Total richness, EPT richness (Ephemeroptera, Plecoptera and Trichoptera), and EPT abundance were significantly higher in perennial than in intermittent reaches (both studied streams). In addition, the biological traits related to dissemination mode, resistant form, and feeding habit were most affected by flow intermittence.
•Both the duration of the dry period and the distance to the nearest perennial reach affected community structure and the related biological traits. Total richness and EPT richness decreased with both increasing duration of the dry period and distance to perennial reaches. Furthermore, the abundance of aerial active taxa increased with both increasing duration of dry period and distance to perennial reaches (both streams).
•Invertebrate assemblages at the most intermittent sites were nested subsets of assemblages at the least temporary and perennial sites (both streams).
In conclusion, our findings support the hypothesis that flow intermittence is a master variable driving river assemblage structure and composition and biological trait distribution (as evidenced from two rivers studied, which belong to different climate types). When flow intermittence increased (quantified as the duration of the dry period and the distance to perennial reaches), taxonomic richness of invertebrate assemblages decreased. In addition, assemblage nestedness most likely resulted from both limited dispersal from source communities of perennial reaches and local extinction due to increasing flow intermittence.
These findings have an important impact on research, management, and monitoring of temporary streams and rivers in the context of climate change; with direct implications for the bioassessment of temporary streams in the context of the European Water Framework Directive. These findings will help to water managers to reformulate current bioassessment and monitoring schemes of temporary river basins, where the effect of flow intermittence on aquatic invertebrate communities has been generally neglected so far.
-Effects of flow intermittence on ground-dwelling arthropod assemblages in channels and fringing terrestrial habitats of temporary streams.
To approach this second objective, terrestrial invertebrate communities were quantitatively collected in temporary streams and the adjacent terrestrial habitats (riparian and upland areas). The main results were:
• Flow intermittence and the duration of the dry period strongly influenced terrestrial arthropod assemblages, not only in the stream channel but also in the adjacent terrestrial habitats (riparian and upland areas).
• The composition of arthropod assemblages differed between flow regime types (perennial and intermittent types), habitat types (channel, riparian and upland areas), and sampling dates (a during a 1-month dry phase). In contrast, taxonomic richness and total abundance were similar between perennial and intermittent reaches, but differed among habitat types, depending on the studied temporary stream.
•In one of the studied streams arthropod abundances peaked in the dry channel and increased with drying time; at the same time abundances decreased in riparian and upland habitats.
In conclusion, the results emphasize the importance of dry channels in temporary rivers as temporal habitats for terrestrial arthropod assemblage and provide evidence that the dry channel may be colonized by both riparian and upland arthropods. Our findings advance the notion that special attention need to be paid to the duration of the dry period, given the concomitant change in the composition and the structure terrestrial arthropods undergo with time.
The findings have a relevant impact on the research and management of temporary rivers, especially in relation to the bioassessment of temporary rivers during the dry phase. Metrics based on terrestrial arthropods may reflect the ecological status of intermittent streams during the dry phase, and therefore should complement existing monitoring strategies that only focus on aquatic organisms. Temporary streams are coupled aquatic and terrestrial ecosystems, and both states need to be adequately considered when understanding and managing them.
-Temporary rivers as corridors for terrestrial fauna during the dry period.
To approach this third objective, a review and conceptual work about the function of corridors for both aquatic and terrestrial animals was conducted (manuscript close to submission). In addition, a field study testing the use of dry river beds by terrestrial vertebrates was performed in two temporary streams. The main results related to the first approach (review and conceptual paper) were:
• Rivers are generally perceived as corridors for aquatic animals embedded in a terrestrial landscape. The presence of IRs in river networks changes this view of river corridors.
• Intermittent rivers are coupled aquatic-terrestrial corridors. In IRs, the alternation of wet and dry periods creates a mosaic of aquatic and terrestrial habitats. IRs are not only suitable pathways for the movement of aquatic species during wet conditions (aquatic corridor), but also for terrestrial species during dry periods (terrestrial corridor).
• Flow intermittence influences the movement of animals in temporary rivers and therefore has major ecological consequences. The movement of aquatic species in temporary rivers is naturally limited during the dry phase (except for flying species, aerial stages of insects, passive wind dispersers). Dry river beds increase the connectivity between patches along river networks and may serve as preferential pathways for terrestrial animals.
Main results related to the second approach were:
•Dry beds were widely used by vertebrates (mammals, reptiles and birds), especially along vegetated stream sections.
•The use of the different habitat types (dry river bed, riparian, upland, and unpaved road) was consistent among vertebrate groups.
•In dry beds, directional tracks were more frequent than non-directional ones, with a prevalence of tracks running parallel to the river line; particularly in summer.
In conclusion, our findings support the idea that temporary rivers act as corridors for terrestrial vertebrates. River beds might be particularly important for long-distance movements along the river course, in contrast to perpendicular movements (i.e. crossings). Finally, the permeability of the surrounding landscape can be a key factor that influences the use of temporary rivers as dispersal and migration corridors.
The findings have strong implication in the management of temporary rivers as landscape corridors. We provide evidence that dry river beds are ecological corridors that increase natural connectivity between patches (e.g. water holes, other suitable habitats). Temporary rivers are both terrestrial and aquatic corridors along entire river networks and, therefore, should be considered and managed within the context of blue and green infrastructures.