Search

The fundamental ecological niche is determined by individuals' ability to cope with abiotic conditions; however, biotic interactions (e.g., competition) can also influence species' distribution ranges, reducing the fundamental niche to the realized niche. Several species of the genera Clibanarius and Calcinus overlap in their distributions. The agonistically dominant Calcinus species inhabits mostly lower intertidal levels, while Clibanarius is more abundant in the abiotically demanding upper strata. Additionally, evidence of microhabitat competitive exclusion shows that the superior competitor, Ca. californiensis, causes the vertical displacement of Cl. albidigitus. However, it is unknown whether competitive exclusion between species of these genera has influenced their distributions at the macroecological scale. We used ecological niche models to compare the distribution and the habitat suitability of species of these genera. We used databases of species occurrences and bioclimatic and geophysical variables to model and map the species' niches. Species of the two hermit crab genera showed strong overlap in their habitat suitability. Calcinus and Clibanarius species occur in broad sympatry at the regional scale without regions of partial overlap that would indicate competitive exclusion. Therefore, competitive exclusion among species of these genera seems to act only on a microhabitat scale in the most dynamic shoreline areas. [ABSTRACT FROM AUTHOR]

When invasive tubenose gobies (Proterorhinus semilunaris) and round gobies (Neogobius melanosotmus) occur in the same invaded ecosystem, the first is almost always displaced by the latter. Here, we report on a series of habitat-oriented laboratory experiments and field surveys aimed at revealing mechanisms that allowed coexistence of both species along the River Dyje (Danube basin). The experiments suggested that (i) both gobiids prefer the same habitat type, i.e., interstitial shelters between rocks, (ii) round goby is stronger, more aggressive competitor and (iii) round goby presence results in shift in tubenose goby habitat use. Field sampling indicated that round and tubenose gobies tended to occupy different microhabitats both along the longitudinal and lateral profile. Tubenose goby was found most often in shallow, near-bank rip-rap composed of smaller rocks, while round goby occurred most often in deeper areas with gravel substrates, larger rocks and faster current. Both species avoided the faster-flowing stretch in the middle of the river. Similar complementarity was also noted in temporal activity patterns, with round goby least active during the night and tubenose goby during the day. Our findings suggest that fine-scale niche separation facilitates the coexistence of these two invasive species, despite large 'broad-scale' niche overlap. [ABSTRACT FROM AUTHOR]

Invasive alien anurans are introduced worldwide in freshwater ecosystems where they can have a strong impact on native organisms such as amphibians. The risk for natives is dependent on the degree of niche overlap and co-occurrence in pond-breeding sites. In the present study, we focused on alien marsh frogs (Pelophylax ridibundus) that are invading nationwide areas in Western Europe and which prey on both caudates and anurans. We assessed aquatic habitat preferences, pond use and environmental niche overlap between invasive populations of marsh frogs and five species of native amphibian prey of the Larzac plateau (southern France). Due to their large environmental niche, marsh frogs have become the most ubiquitous amphibians in the area. Occupancy models revealed that they had aquatic habitat preferences (e.g., water depth and aquatic vegetation) similar to most species of native amphibians. This resulted in a large overlap between the environmental niche of the invader and its potential prey. The frequent coexistence in ponds therefore exposed native species to predation risk and other potential disturbances caused by marsh frogs. Altogether, these results highlight on the risks posed by such opportunist invaders for native amphibians that occur in their wide invasion range. [ABSTRACT FROM AUTHOR]

Small nearshore fishes are an important part of lacustrine and functional diversity and link pelagic and benthic habitats by serving as prey for larger nearshore and offshore fishes. However, the trophic complexity of these small nearshore fishes is often unrecognized and detailed studies of their role in food webs are lacking. Here, we examined niche space patterns of small nearshore fish species using Bayesian analyses of carbon and nitrogen stable isotope data in nine freshwater lakes that are among the largest lakes in Minnesota. We found considerable variability in niche areas within species and high variability in niche overlap across species. At the assemblage level, niche overlap (average diet overlap of all species pairs at a lake) decreased as whole-lake species richness increased, possibly indicating a greater degree of resource specialization in more speciose lakes. Overall fish niche space was weakly but significantly related to niche space of their invertebrate prey. Although nearshore benthic resources contributed to fish diets in all lakes, all fish species also had non-negligible and variable contributions from pelagic zooplankton. This inter- and intraspecific variability in trophic niche space likely contributes to the multi-level trophic complexity, functional diversity, and potentially food web resilience to ecosystem changes. [ABSTRACT FROM AUTHOR]

Despite the importance of shredders in organic matter processing in streams, information about the habitat specificities of different taxa is scarce. Herein, we evaluated the habitat preferences of invertebrate shredders in tropical forest streams. A total of 72 leaf patches were sampled in three Atlantic Forest streams (SE Brazil). For each sample, 20 environmental variables were measured, including water properties and characteristics of the leaf patch. We used an Outlying Mean Index analysis to evaluate the niche breadth and overlap of each taxon found as well as habitat preferences. In total, we found 14 shredder taxa in 68 leaf patches, and the gradient of environmental conditions influenced the distribution of most taxa. Considering taxa that occurred in atypical habitats in the study sites, Blaberidae (semiaquatic cockroaches) and Trichodactylus fluviatilis (Decapoda) showed niche segregation, while Macrobrachium potiuna (Decapoda), Tupiperla (Plecoptera), and Nectopsyche (Trichoptera) showed niche overlap. On the other hand, Heterelmis (Coleoptera), Stenochironomus (Diptera), Phylloicus major, and Triplectides gracilis (Trichoptera) occurred in typical habitats. These results showed that shredder taxa had different habitat preferences. The observed differences in niche breadths and habitat specificities among taxa probably result in different leaf processing rates across leaf patches in Atlantic Forest streams. [ABSTRACT FROM AUTHOR]

Invasive species may affect the equilibrium of natural communities, competing for resources and occupying niches of the native biota. Dendrocephalus brasiliensis (DEN) has potential to aquaculture, although its use is concerning, since DEN is allochthone in some regions of Brazil. Here, we aimed to study the possible effects of DEN on three cladocerans Moina micrura (MOI), Macrothrix flabelligera (MAC) and Daphnia laevis (DAPH). We performed microcosm experiments combining different cladoceran species in mono- and polycultures in the presence and absence of DEN by evaluating density, biomass, production, stages of development and turnover. MOI was competitive excluded when in 2-species polycultures with MAC and DAPH, and in 4-species polycultures with MAC, DAPH and DEN together. Since MOI survived when cultured with MAC and DAPH in 3-species polycultures, DEN possibly played a role on MOI suppression. Regarding density, DAPH had a slightly suppression when exposed separately with MOI, although MAC had higher production in the presence of MOI. Development stages with similar body size apparently competed more intensely for resources. Our results indicate that DEN has potential to invade ecosystems, destabilizing native zooplankton communities, since it affected MAC and DAPH, thus altering their competitive advantage, besides contributing to MOI exclusion. [ABSTRACT FROM AUTHOR]

In the Amazon Basin, several species of herbivorous serrasalmid fishes inhabit rapids, but it is unknown if they partition food resources during the annual low-water period when fish densities are high within greatly reduced volume of aquatic habitat. We investigated the trophic ecology of juveniles and adults of three species, Myleus setiger, Ossubtus xinguense, and Tometes kranponhah, common in rapids of the Xingu River during the low-water period. Diets, stable isotope ratios of muscle tissue, and functional traits were analyzed for 59 specimens of M. setiger, 175 of O. xinguense and 215 of T. kranponhah. The three species overlapped in dietary and isotopic space, with adult O. xinguense being most divergent. Juvenile and adult T. kranponhah and juvenile O. xinguense, two groups with broad diets, had lowest trophic positions estimated from isotopic data. Adult O. xinguense had the highest trophic position despite having large amounts of Podostemaceae in the diet. High trophic overlap during the low-water period suggests that either food resources are not limiting, or niches are partitioned by other means. Differences in functional traits of the three serrasalmids could be associated with differential efficiencies of swimming and feeding within microhabitats that vary according to water velocity and/or structural complexity. [ABSTRACT FROM AUTHOR]

We aim to test the hypothesis that an assemblage of characid fishes coexist by partitioning food resources. We calculated dietary niche overlap of four syntopic species of the Characidae using gut content analysis. Secondly, we used a carbon (C) and nitrogen (N) isotope Bayesian mixing model to estimate relative assimilation. All characids consumed large proportions of plant material and aquatic insects; however, Pianka's index indicated low dietary overlap among species throughout most of the sampling period. The low degrees of dietary overlap were due to discrepancies in the relative consumption of Ephemeroptera and aquatic insect remains. Secondly, there was high correspondence between the gut content analyses and isotope mixing model estimates. Astyanax xiru and Bryconamericus iheringii were the only species that ingested and assimilated large fractions of aquatic plants and algae, respectively. Astyanax procerus consumed and assimilated large fractions of terrestrial invertebrates, whereas Bryconamericus sp. assimilated mainly aquatic invertebrates. Therefore, we demonstrate that the assimilated nutrients were consistent with the relative consumption of food items. These results are consistent with the hypothesis that this characid assemblage may coexist via resource partitioning. [ABSTRACT FROM AUTHOR]

Habitat suitability indices indicate how fish species respond to different habitat types. We assessed effects of habitat characteristics on fish distribution in an equatorial lake, Lake Naivasha, Kenya, where habitats vary according to substrate, depth and turbidity. Using monthly data between 2008 and 2010 using multi-mesh gill nets, catch per unit effort was used as a relative abundance measure to identify how habitat variables drive fish distribution. The focus was on commercial fishes: two introduced species ( Cyprinus carpio and Micropterus salmoides) and two naturalised species ( Oreochromis leucostictus and Tilapia zillii). Analyses revealed distinct preferences for different habitat variables by all commercial species except for C. carpio. For example, O. leucostictus preferred shallow waters with silt-clay substrates whilst M. salmoides preferred deeper waters with sandy/rocky substrates. Conversely, C. carpio showed no specialised habitat requirements. Niche overlaps were significantly lower between O. leucostictus and its respective sympatric species than between other species, a likely result of its territorial behaviour. The continued environmental degradation of Lake Naivasha may imperil the preferred habitats of the niche restricted M. salmoides, O. leucostictus and T. zillii. By contrast, the ubiquity of C. carpio may facilitate their invasion, and consequently sustain their dominance in the lake's commercial fishery. [ABSTRACT FROM AUTHOR]

Seagrass meadows provide both habitats and a range of food sources for macrofaunal communities. These functions facilitate the coexistence of less mobile invertebrates (in comparison with mysids, such as amphipods) that are associated with seagrass leaves, and may also enhance the coexistence of highly mobile invertebrates such as mysid. We investigated the function of seagrass in supporting the coexistence of two mysid species, Neomysis awatschensis and N. mirabilis. These taxa are dominant in seagrass ecosystems of temperate coastal areas. We compared patterns of habitat use between the two species at mesoscales (among seagrass patches) and microscales (among seagrass leaves) by performing field surveys and laboratory experiments. The field survey results showed positive correlations in the abundance of the two mysid species, indicating that both species select similar habitats at the mesoscale level. In the laboratory experiments, the pattern of microhabitat selection (fundamental habitat) was similar for both species, even at increased densities and with the presence of an immobile habitat-competitor (the gastropod Barleeia angustata) on the leaves. However, this pattern changed significantly when a food source (epiphytic microalgae) was present on the leaves. This result indicates that (i) inter- and intraspecific interference competition does not affect microhabitat selection in these two mysids and (ii) both Neomysis species use similar habitats at the feeding stage. Although these two closely related mysids species may have similar requirements for microhabitat and food, the evidence that they did not act as competitors is attributable to unrestricted microhabitat and food (e.g., epiphytic algae) in the presence of seagrass vegetation. [ABSTRACT FROM AUTHOR]

This research characterized the feeding ecology of the fish community of the upper-middle course of Paraitinga River, located within the Upper Tietê River Basin, a peculiar Atlantic Forest area, regarded as a hotspot for fish conservation. Considering the several anthropogenic modifications, knowledge of the trophic structure might contribute to a better understanding of the factors that maintain the present fish community. Fish were collected with electrofishing equipment at 16 sites with different riparian vegetation, including native forest, secondary forest, pasture, and Eucalyptus, during the dry and rainy season of 2004/2005. Results obtained for 15 species indicated a predominance of insectivores and herbivore-detritivores along the course and an increase of total biomass, specifically of the herbivores-detritivores at the pasture sites, which seemed to be mediated by specific habitat features, which included open canopy, high water speed, and deeper areas. Strategies of resource use indicated that 47% of total combination pairs showed high overlap, but competition seemed to be minimized through low co-occurrence, spatial segregation, and abundance of food resources. Niche width was broad for all species, with no significant differences occurring among sites, seasons, and upper and lower course. With regard to the ongoing modifications in riparian zone conditions in this area, the implications of these findings for regional biodiversity conservation are discussed. [ABSTRACT FROM AUTHOR]

Spatial resource overlap by benthic invertebrates was investigated between stones in 11 freshwater habitats (10 streams and a wind-swept lake shore) of similar physicochemical nature but different thermal and hydrologic stability in the Cass-Craigieburn region, New Zealand. Both overlap and breadth of stone use by the invertebrate taxa decreased as stability declined, in part because of the lower number of species available with which to share resources at unstable sites. Although there was no evidence for resource partitioning of stones, communities at stable sites and on more stable substrates differed from those that would have been expected to accumulate by chance colonisation alone. Stone assemblages at unstable sites are dominated by the same general suite of species well suited to surviving disturbances, while conditions at stable sites allow more specialised taxa to colonise individual stones differentially. [ABSTRACT FROM AUTHOR]

Between January 1993 and January 1995, the number of Great Cormorants (Phalacrocorax carbo) using Lake Naivasha, Kenya (00° 45' S, 36° 20' B) for foraging and resting increased 56%, while the number of sympatric Long-tailed Cormorants (Phalacrocorax africanus) decreased 64%. In 1995 and 1996, we documented habitat changes and conducted monthly population and resource-use surveys of the two species in an attempt to discover the most likely reasons for these changes. The increase in Great Cormorants was probably the result of immigration from nearby Lake Nakuru due to extreme water level reductions there. Lake Naivasha also experienced falling water levels and transparency during this period, but these changes were not as severe and are not considered likely reasons for the decline in Long-tailed Cormorant numbers. Despite some probable dietary overlap, the two species were well separated in terms of foraging locations, foraging methods, resting habitats and breeding timing. The decline in Long-tailed Cormorant numbers may be connected with increased disturbance by fishermen along the lake littoral, this species' primary feeding location. [ABSTRACT FROM AUTHOR]