Dispersal of aquatic organisms by waterbirds: a review of past research and priorities for future studies

1. Inland wetlands constitute ecological islands of aquatic habitat often isolated by huge areas of non-suitable terrestrial habitats. Although most aquatic organisms lack the capacity to disperse by themselves to neighbouring catchments, many species present widespread distributions consistent with frequent dispersal by migratory waterbirds.
2. A literature review indicates that bird-mediated passive transport of propagules of aquatic invertebrates and plants is a frequent process in the field, at least at a local scale. Both endozoochory (internal transport) and ectozoochory (external transport) are important processes.
3. The characteristics of the dispersed and the disperser species that facilitate such transport remain largely uninvestigated, but a small propagule size tends to favour dispersal by both internal and external transport.
4. We review the information currently available on the processes of waterbird-mediated dispersal, establishing the limits of current knowledge and highlighting problems with research methods used in previous studies. We also identify studies required in the future to further our understanding of the role of such dispersal in aquatic ecology.     

Nestedness patterns of container-dwelling mosquitoes: effects of larval habitat within variable terrestrial matrices

Distributions of mosquito larvae likely are a consequence of multiple factors, although two commonly studied factors (quality of the larval environment and the terrestrial matrix in which these habitats reside) have rarely and simultaneously been varied in the field to understand distributions of larvae. We monitored aquatic containers of two leaf detritus levels within a forest, prairie, and industrial habitat across five months to understand the temporal and spatial colonization of aquatic invertebrates in Northcentral Illinois, USA. Data were collected monthly on mosquito populations and the composition of other invertebrates colonizing containers. Overall, six species of mosquitoes colonized containers, with Culex restuans and Aedes triseriatus having the highest relative abundances. There were strong seasonal abundance patterns for these two mosquito species, with the dominant species changing over time in the forest habitat. The responses of other mosquito taxa were more variable, with abundances reflective of either the terrestrial matrix or larval habitat quality. High detritus containers supported the highest abundances of most species encountered, regardless of habitat. Non-mosquito taxa were less common numerically, but analyses suggested that some taxa, such as syrphid larvae, often co-occurred with mosquitoes. Nested subset analysis indicated communities were strongly nested, and that both habitat type and detritus level were important in explaining nested patterns of aquatic invertebrates. Our data show that both the larval habitat and the surrounding terrestrial matrix shape patterns of container mosquitoes, and that other container invertebrates vary in similar ways as mosquitoes. Handling editor: K. Martens     

Flooding compromises compensatory capacity of an invasive plant: implications for biological control

Plant compensatory growth is proposed to be insidious to biological control and known to vary under different environmental conditions. However, the effects of microsite conditions on compensation capacity and its indirect impacts on biological control of plant invaders have received little attention. Alligator weed, Alternanthera phioxeroides, is an invasive plant worldwide, growing in both aquatic and terrestrial habitats that are often affected by flooding. Biological control insects have been successful in suppressing the plant in many aquatic habitats but have failed in terrestrial habitats. To evaluate the impact of flooding on compensation capacity, we conducted common garden and greenhouse experiments in which plants were grown under different moisture conditions (aquatic versus terrestrial). Our results show that plants were able to fully recover from continued herbivory in the terrestrial habitat, but failed in the aquatic habitat, indicating a flooding-regulated plant compensatory capacity. Also, the grazed plants increased below-ground growth and reproductive root bud formation in the terrestrial habitat, but there was no such difference in the aquatic habitat. Our findings suggest that the differing plant compensatory capacity, affected by flooding, may explain the different biological control efficacy of alligator weed in aquatic and terrestrial habitats. Understanding mechanisms in plant invader compensation in different microsite conditions is important for improving management efficiency.     

Opportunistic exploitation of dinosaur dung: fossil snails in coprolites from the Upper Cretaceous Two Medicine Formation of Montana

Multiple associations of fossil snails with dinosaur coprolites demonstrate that snails and dinosaurs not only shared ancient habitats but were trophically linked via dinosaur dung. Over 130 fossil snails representing at least seven different taxa have been found on or within herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana. The terrestrial snail Megomphix is the most common taxon, but three other terrestrial taxa (Prograngerella, Hendersonia and Polygyrella) and three aquatic snails (Lioplacodes, ?Viviparus and a physid) also occur in coprolites. At least 46% of the shells in the faeces are whole or nearly so, indicating that most (if not all) of the snails were not ingested by dinosaurs, but were post‐depositional visitors to the dung pats. The sizeable, moist and microbially enriched dinosaur faeces would have provided both food and roosting sites for the ancient snails, and the large number of snail–coprolite associations reflect recurring, opportunistic exploitation of dung. The terrestrial taxa in the coprolites suggest that this Late Cretaceous locality included sufficiently moist detrital or vegetative cover for snails when dinosaur dung was not present. The aquatic snails probably entered the faeces during flood events. Dinosaur dung would have provided an abundant but patchy influx of resources that was probably seasonally available in the ancient environment.     

Does the management of surrounding terrestrial habitats increase the tendency of odonates to leave aquatic habitats?

Generally, dragonflies and damselflies (odonates) are considered aquatic invertebrates. However, the ecological requirements of their adults are not different from those of fully, terrestrial insects. Surprisingly, there is a very little information on whether the management and structure of surrounding habitats has any influence on the diversity and seasonal dynamics of odonates. This is important to know because recently, a large proportion of freshwater habitats in Central Europe have becomes surrounded by intensively managed habitats. The aim of this study was to investigate the effects of different types of terrestrial habitats on their long-term utilization by dragonflies and damselflies. I assumed that this pattern varied over time; therefore, I used generalized additive mixed models to analyze the effects of management on seasonal changes in the abundance of individuals in terrestrial environments. From my results, it was evident that the management practices of surrounding terrestrial habitats had a significant impact on the population dynamics of dragonflies. The abundance of dragonfly adults in surrounding terrestrial habitats increased toward the end of the season. However, this was only, when the natal aquatic habitat was not affected by fish farming and was able to supply surrounding terrestrial habitats with offspring. This was evidenced by the fact that, compared to areas with extensive water management, in sites with fish farming, seasonal increases in abundance was negligible. There is no doubt that the structure of surrounding terrestrial habitats has a significant influence on the diversity of terrestrial invertebrates. However, we must not forget that terrestrial habitats, regardless of their management, are not able to replace the poor quality of the aquatic (natal) habitat. Interestingly, the abundance of damselflies decreased toward the end of the season, regardless of the management practices of the surrounding areas. This indicates that their dynamics is more controlled by time stress or other similar mechanisms than that of dragonflies.     

The fauna of dynamic riverine landscapes

1.  Riverine landscapes are heterogeneous in space (complex mosaic of habitat types) and time (expansion and contraction cycles, landscape legacies). They are inhabited by a diverse and abundant fauna of aquatic, terrestrial and amphibious species.
2.  Faunal distribution patterns are determined by interactive processes that reflect the landscape mosaic and complex environmental gradients. The life cycles of many riverine species rely upon a shifting landscape mosaic and other species have become adapted to exploit the characteristically high turn-over of habitats.
3.  The complex landscape structure provides a diversity of habitats that sustains various successional stages of faunal assemblages. A dynamic riverine landscape sustains biodiversity by providing a variety of refugia and through ecological feedbacks from the organisms themselves (ecosystem engineering).
4.  The migration of many species, aquatic and terrestrial, is tightly coupled with the temporal and spatial dynamics of the shifting landscape mosaic. Alternation of landscape use by terrestrial and aquatic fauna corresponds to the rise and fall of the flood. Complex ecological processes inherent to intact riverine landscapes are reflected in their biodiversity, with important implications for the restoration and management of river corridors.     

Dispersal of freshwater invertebrates by large terrestrial mammals: a case study with wild boar (Sus scrofa) in Mediterranean wetlands

1. Many invertebrates inhabiting insular aquatic habitats rely on external agents or vectors to disperse. Besides water connections and wind, waterfowl and amphibians are known to mediate passive dispersal of freshwater invertebrates. However, the possibility of dispersal by terrestrial mammals has been largely overlooked. 2. We investigated the potential of both external and internal zoochorous dispersal of aquatic invertebrates by the wild boar (Sus scrofa) in Mediterranean wetlands in the Camargue (France). As wild boar frequently visit wetlands for feeding and wallowing purposes, we hypothesized that they may be important passive dispersal vectors of aquatic invertebrates at a local scale. Dried mud was collected from selected ‘rubbing trees’ used by boars to dispose of parasites. Additionally, faecal pellets were collected from different locations in the wetland area. 3. Seventeen freshwater invertebrate taxa including rotifers, cladocerans, copepods and ostracods hatched from sediment obtained from ‘rubbing trees’, while invertebrates hatching from dried faeces (10 taxa) were mainly rotifers. Dispersing invertebrates were collected up to 318 m from a nearest potential dispersal source. Both abundance and richness of invertebrates significantly decreased with dispersal distance. 4. Our results demonstrate that large mammals such as wild boar can act as dispersal vectors of aquatic invertebrates at a local scale in the wetland area of the Camargue and suggest that external transport may be quantitatively more important than internal transport. As wallowing (mud bathing) is common in many terrestrial mammals, this mode of dispersal may be quite widespread.     

Salinity as a driver of aquatic invertebrate colonisation behaviour and distribution in the wheatbelt of Western Australia

To understand how environmental change will modify community assembly and the distribution of organisms it is valuable to understand mechanisms that drive the occurrence of organisms across the landscape. Salinisation of agricultural land in southwest Western Australia, as a result of land clearing, is a widespread environmental change, which threatens numerous taxa, but provides an opportunity to elucidate such mechanisms. Although salinisation affects terrestrial fauna and flora, the greatest impacts are seen in wetlands and waterways. Many aquatic insect taxa colonise ephemeral water bodies directly as adults or by oviposition. Few empirical studies, however, evaluate the influence of abiotic factors, such as water body salinity, on the colonisation behaviour of aquatic fauna. We conducted a manipulative experiment using mesocosms to test whether colonising insect fauna select aquatic habitats based upon salinity. We found that halosensitive fauna selected less saline mesocosms for oviposition and colonisation, demonstrating that behaviour can influence the distribution of aquatic organisms. Additionally, we utilised field surveys of insects from ephemeral water bodies across a broad region of southwest Western Australia to determine if mesocosm results reflected field observation. The abundance of the same insect taxa and taxonomic groups in the field were highly variable and, with the exceptions of Culex australicus Dobrotworksy and Drummond and Anopheles annulipes Giles (Diptera: Culicidae), did not show similar patterns of distribution to those observed in the mesocosm experiment. Both mesocosm and field assemblages exhibited similar and significant trajectories associated with the salinity gradient, even though there were differences in assemblage structure between the two. Our findings give empirical support to the importance of behaviour in the spatial distribution and assembly of some aquatic insects. Handling editor: K. Martens     

Cohort studies on mosquito (Diptera: Culicidae) larvae living in the water-filled floral bracts of Heliconia aurea (Zingiberales: Musaceae)

Abstract. 1. An experimental and observational study of the three species of mosquito larvae living in the water-filled floral bracts of Heliconia aurea at Rancho Grande, Venezuela, was designed to determine if each mosquito species forms instar cohorts and excludes conspecifics of younger instars. This study was motivated by a statement of Maguire (1971) who suggested that mosquito larvae in Puerto Rican Heliconia inflorescences form instar cohorts and exclude younger mosquitoes from the floral bracts.
2. Field observations of naturally occurring populations of mosquito larvae from fifty-three H.aurea inflorescences give no indication that cohorts are formed for Wyeomyia felicia and Culex bihaicolus . However, there is strong evidence that cohorts of Trichoprosopon digitatum occur. These cohorts are not structured by larval competition but by female preference of the youngest bracts as oviposition sites and by large T.digitatum larvae feeding on smaller con-specifics.
3. Field experiments show that first instar W.felicia and C.bihaicolus survive as well over a 6 day period in the presence of third instar conspecifics as they do when all mosquito larvae in an experimental bract are first instars.     

Offspring performance in dynamic habitats: key factors for a riparian carabid beetle

Abstract.  1. Knowledge of the ecology of carabid species is largely restricted to adults, although larval mortality is assumed to be the key factor in overall mortality. As low-mobility larvae are unable to avoid unfavourable conditions, habitat selection of reproducing adults should be clearly affected by the habitat factors which determine offspring performance.
2. The present study examines the key habitat factors governing the distribution patterns of Bembidion velox larvae and adults on the river banks of the River Elbe by means of habitat suitability models. The validity of the determined habitat factors for offspring performance and survival was tested in laboratory experiments.
3. In the field, B. velox adults as well as larvae show a strong association with semi-terrestrial, sandy, open soil habitats.
4. In the laboratory, overall mortality of larvae reared in different substrates was lowest in sand of medium grain size mixed with fine and coarse sand. The first larval instars in particular reacted sensitively to variations in grain size. Furthermore, flood resistance of eggs was demonstrated, as 90% of larvae hatched under permanently flooded conditions.
5. Short development times were recorded, with 4–7 days for hatching of young larvae from eggs after oviposition and approximately 28 days for the development of adults from newly hatched larvae. This probably increases the survival probability for the pre-imaginal stages in dynamic habitats.
6. In conclusion, it can be said that reproductive success is strongly dependent on oviposition site selection by adults as this reflects the ecological demands of the immature stages.     

What predicts the use by brook trout (Salvelinus fontinalis) of terrestrial invertebrate subsidies in headwater streams?

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Successional phases and species replacements in freshwater rock pools: towards a biological definition of ephemeral systems

1. In temporary aquatic habitats, time is probably the dominant environmental factor affecting community composition, mainly by setting constraints on colonization success and the replacement of taxa over time. The mechanism and effect of a decreasing inundation period on community development, mostly in terms of truncation, are still poorly documented. The permanent and ephemeral components of temporary communities are expected to be differently influenced by the degree of persistence of the habitat. 2. To study the effect of time on invertebrate community assembly and dynamics in a short duration type of temporary aquatic habitat, we monitored 16 ephemeral rock pools which persisted from less than a week to about 1 month at two rock pool sites in semi‐arid south‐eastern Botswana. Data were collected every 2 days during a full inundation cycle. 3. All communities were initially assembled by permanent residents recolonizing the habitat from egg banks and were later joined by actively dispersing ephemeral taxa. Species replacements only occurred in two pools. Concurrent with a decrease in the densities of Branchipodopsis wolfi, population sizes of Leberis sp. and Culicidae (Aedes sp. and Anopheles sp.) increased in these pools. Although it was possible to distinguish two successive phases at one rock pool site, community assembly was generally a gradual process determined by dispersal strategies of the inhabitants. Additional rains after initial filling triggered dispersal by ephemeral taxa, mainly Micronecta youngiana and Hydroglyphus infirmus, and positively influenced colonization success. 4. Decreasing persistence shortens community development down to a critical point below which lack of time eliminates the possibility of species replacement. Based on these findings, we define ephemeral waters as aquatic habitats lacking species replacements. Other temporary water types have a relatively longer persistence, permitting successional replacement of species.     

Effects of substratum stability on diversity of stream invertebrates during baseflow at two spatial scales

1. The effects of substratum stability on the diversity of stream invertebrates were assessed at two spatial scales in a Japanese stream during baseflow, from May to June 1998. Deposition and erosion were examined separately as distinct elements of substratum stability by a newly developed method using small steel pins. Stream invertebrates were sampled after 28 days of measurement of substratum stability. We also measured physical environmental variables, current velocity and depth, and food resource parameters including periphyton and particulate organic matter (POM) standing crops.
2. At the scale of the habitat patch, the effects of substratum stability on invertebrates were overwhelmed by those of POM standing crop. Moreover, higher taxon richness at high abundance may simply result from a higher likelihood of more taxa being included in samples. Therefore, this small scale revealed no role for substratum stability in explaining spatial pattern of community diversity.
3. At the reach scale ( n =10), taxon richness and evenness peaked at an intermediate level of deposition, whereas invertebrate abundance did not show any significant relationship. This result, and the pattern of relative abundance of common taxa, implies that the diversity of stream invertebrates was determined by subtle substratum movements and by the habitat preference of each taxon.
4. The difference in the determinant of community parameters between the habitat patch and the reach affirm the importance of a cross-scale analysis to choose an appropriate spatial scale for investigating the community structure of stream invertebrates. Prominent effects of substratum stability, particularly the deposition of substratum particles, during baseflow suggest that subtle and constant movement of small substratum particles can contribute to determine the diversity of stream invertebrates.     

Food habits of an endangered Japanese frog, Rana porosa brevipoda

We examined the diet of an endangered frog, Rana porosa brevipoda inhabiting rice fields of western Japan, by forced regurgitation of stomach contents. The frog diet consisted of a wide variety of arthropods, and ants, beetles, dipterans, bugs, orthopterans, and spiders, which were especially prominent. These prey taxa were also collected in large numbers by sweep-net samplings made in the frog habitat, and relative abundances of prey taxa in frog diet and those in sweep samples were found to be significantly correlated. Aquatic forms did not contribute much to the frog diet, but were found to be taken more frequently and in larger numbers in irrigated fields than in drained fields. These findings suggest that prey availability around frog habitat is very important to regulate the food items of R. p. brevipoda. On the other hand, terrestrial components of frog habitats are indicated to be important because the frog highly depended on terrestrial invertebrates. From these results, we consider it imperative to preserve terrestrial components linked with aquatic environments to conserve biodiversity in rice field ecosystems.     

Biodiversity in the floodplain of Saône: a global approach

Biodiversity of European floodplains is seriously threatened mainly due to (1) modifications of river courses such as channelisation or embankments, and (2) changes in traditional agricultural practices (i.e. usually pastures), into intensive production using drainage and fertilisation. A upstream-downstream survey of the Saône floodplain (France) has been done to identify the contribution of habitats to the floodplain biodiversity. Selected taxa were aquatic and terrestrial vegetation, Odonata, Coleoptera, Amphibians, and birds. The taxa were sampled in different habitat types that were: forests, grasslands and aquatic habitats. Tributary confluences with the river and cut-off channels contributed greatly to the floodplain diversity according to their invertebrates and aquatic vegetation communities. The abundance of rare species (benefitting of a national or regional protection status) was the highest in hygrophilous grasslands. Moreover, we demonstrated that diversity of breeding bird communities was correlated with the size of these habitats. We demonstrated also that alluvial forests contributed to maintain some particular species as Middle-spotted Woodpecker (Dendrocopus medius), while new plantations were colonized by openland bird communities sensible to the edge effect. Grassland fragmentation for agriculture appeared to be a major cause in biodiversity loss. Any alteration of the floodplain dynamics must be avoided to preserve the present diversity of riverine wetlands.     

Aquatic invertebrates in riverine landscapes

1. Riverine systems consist of a mosaic of patches and habitats linked by diverse processes and supporting highly complex communities. Invertebrates show a high taxonomic and functional diversity in riverine systems and are in several ways important components of these systems. Their distribution patterns, movements and effects on ecological flows, testify to their importance in various landscape ecological processes. This paper reviews the invertebrate literature with respect to patterns and processes in the riverine landscape. 2. The distribution of invertebrates in riverine habitats is governed by a number of factors that typically act at different scales. Hence, the local community structure can be seen as the result of a continuous sorting process through environmental filters ranging from regional or catchment‐wide processes, involving speciation, geological history and climate, to the small‐scale characteristics of individual patches, such as local predation risk, substratum porosity and current velocity. 3. Dispersal is an important process driving invertebrate distribution, linking different ecological systems across boundaries. Dispersal occurs within the aquatic habitat as well as into the terrestrial surrounding, and also over land to other waterbodies. New genetic techniques have contributed significantly to the understanding of aquatic invertebrate dispersal and revealed the importance of factors such as physical barriers, synchrony of emergence and taxonomic affiliation. 4. Invertebrates affect the cycling of nutrients and carbon by being a crucial intermediate link between primary producers, detritus pools or primary consumers, and predators higher up in the trophic hierarchy. Suspension feeders increase the retention of carbon. The subsidies of aquatic invertebrates to the terrestrial ecosystem have been shown to be important, as are reciprocal processes such as the supply of terrestrial invertebrates that fall into the water. 5. Future studies are needed both to advance theoretical aspects of landscape ecology pertaining to the invertebrates in riverine systems and to intensify the experimental testing of hypotheses, for example with respect to the scaling of processes and to linkages between the terrestrial and aquatic systems. Another promising avenue is to take advantage of naturally steep environmental gradients, and of systems disturbed by humans, such as regulated rivers. By comparison with unimpaired reference sites, the mechanisms involved might be identified. The use of `natural' experiments, especially where environmental gradients are steep, is another technique with great potential.     

Distinctive invertebrate assemblages in rockface seepages enhance lotic biodiversity in northern New Zealand

We measured water quality, recorded physical habitat characteristics and collected aquatic invertebrates from 17 rockface seeps, five springs and five streams in a geologically diverse region of New Zealand's North Island to investigate factors influencing invertebrate distribution and community composition within and among these habitats. A total of 147 aquatic invertebrate taxa was found; 84 taxa occurred in seepage samples and 53% of these were found only in those habitats, including several new species. Where paired stream-seepage comparisons could be made, seeps contributed on average 35% of new species to the total species pool. The invertebrate faunas of all habitats were dominated taxonomically by Trichoptera and Diptera, but seepages were relatively depauperate in Ephemeroptera and richer in Coleoptera taxa compared to streams and springs. Seepage faunas were dominated numerically by Mollusca, and had lower percent abundance of aquatic insects (23% overall) compared to springs (77%) and streams (93%). Seepages underlain by different geologies generally had distinct water quality signatures, with seeps draining greywacke, sandstone and volcanic rocks grouping close to their receiving streams in a Principal Component Analysis. Seepage invertebrate community composition reflected underlying geology and associated differences in water chemistry, as well as seepage size and cover by moss. Incorporation of seepage habitats into conservation planning and aquatic ecosystem protection, and maintenance of their function and connectivity with lotic and groundwater ecosystems are important considerations for freshwater biodiversity management. Maintenance of riparian plant cover over seepages should help sustain supplies of organic matter, moss cover and shade, providing habitat complexity and low water temperatures.     

The influence of habitat structure and flow permanence on invertebrate communities in karst spring systems

The macroinvertebrate fauna of five karst (limestone) springbrook systems with contrasting physical habitat and discharge patterns were investigated to examine the role of flow permanence and habitat structure on macroinvertebrate community composition. Clear physical differences were identified between perennial and intermittent springs and individual sampling stations. However, flow permanence, water temperature and the input of leaf litter exerted a greater influence on the aquatic invertebrate community than habitat structure. Perennial sites were characterised by a greater abundance of macroinvertebrates and greater Ephemeroptera, Plecoptera and Trichoptera (EPT) richness than intermittent sites. The fauna of all of the springbrook systems examined were dominated by relatively common and ubiquitous taxa (e.g. Gammarus pulex) although a number of taxa displaying life cycle adaptations to ephemeral aquatic habitats (e.g. Limnephilus auricula and Stenophylax permistus) were recorded at intermittent sites.     

Home Range,Movement, and Distribution Patterns of the Threatened Dragonfly Sympetrum depressiusculum (Odonata: Libellulidae): A Thousand Times Greater Territory to Protect?

Dragonflies are good indicators of environmental health and biodiversity. Most studies addressing dragonfly ecology have focused on the importance of aquatic habitats, while the value of surrounding terrestrial habitats has often been overlooked. However, species associated with temporary aquatic habitats must persist in terrestrial environments for long periods. Little is known about the importance of terrestrial habitat patches for dragonflies, or about other factors that initiate or influence dispersal behaviour. The aim of this study was to reveal the relationship between population dynamics of the threatened dragonfly species Sympetrum depressiusculum at its natal site and its dispersal behaviour or routine movements within its terrestrial home range. We used a mark–release–recapture method (marking 2,881 adults) and exuviae collection with the Jolly–Seber model and generalized linear models to analyse seasonal and spatial patterns of routine movement in a heterogeneous Central European landscape. Our results show that utilisation of terrestrial habitat patches by adult dragonflies is not random and may be relatively long term (approximately 3 mo). Adult dragonflies were present only in areas with dense vegetation that provided sufficient resources; the insects were absent from active agricultural patches (p = 0.019). These findings demonstrate that even a species tightly linked to its natal site utilises an area that is several orders of magnitude larger than the natal site. Therefore, negative trends in the occurrence of various dragonfly species may be associated not only with disturbances to their aquatic habitats, but also with changes in the surrounding terrestrial landscape.     

Responses to River Inundation Pressures Control Prey Selection of Riparian Beetles

Background

Riparian habitats are subjected to frequent inundation (flooding) and are characterised by food webs that exhibit variability in aquatic/terrestrial subsidies across the ecotone. The strength of this subsidy in active riparian floodplains is thought to underpin local biodiversity. Terrestrial invertebrates dominate the fauna, exhibiting traits that allow exploitation of variable aquatic subsidies while reducing inundation pressures, leading to inter-species micro-spatial positioning. The effect these strategies have on prey selection is not known. This study hypothesised that plasticity in prey choice from either aquatic or terrestrial sources is an important trait linked to inundation tolerance and avoidance.

Method/Principal Findings

We used hydrological, isotopic and habitat analyses to investigate the diet of riparian Coleoptera in relation to inundation risk and relative spatial positioning in the floodplain. The study examined patch scale and longitudinal changes in utilisation of the aquatic subsidy according to species traits. Prey sourced from terrestrial or emerging/stranded aquatic invertebrates varied in relation to traits for inundation avoidance or tolerance strategies. Traits that favoured rapid dispersal corresponded with highest proportions of aquatic prey, with behavioural traits further predicting uptake. Less able dispersers showed minimal use of aquatic subsidy and switched to a terrestrial diet under moderate inundation pressures. All trait groups showed a seasonal shift in diet towards terrestrial prey in the early spring. Prey selection became exaggerated towards aquatic prey in downstream samples.

Conclusions/Significance

Our results suggest that partitioning of resources and habitat creates overlapping niches that increase the processing of external subsidies in riparian habitats. By demonstrating functional complexity, this work advances understanding of floodplain ecosystem processes and highlights the importance of hydrological variability. With an increasing interest in reconnecting rivers to their floodplains, these invertebrates represent a key functional element in ensuring that such reconnections have demonstrable ecological value.