Use of trophic ecology of omnivorous fish and abiotic factors as supporting tools for assessing environmental impacts in a neotropical river.

The study of diet is one of the mechanisms by which competition for resources between species that cohabit in the same ecosystem can be inferred. Therefore, the relationships of the indices that measure specialization in the diet of fish species are necessary to characterize the nutritional quality of these populations and the ecosystem's environmental health. Three species of catfish were selected: one invasive (Clarias gariepinus) and two natives (Trachelyopterus striatulus and Rhamdia quelen), with similar distribution along the Guapi-Macacu River, in the Guapimirim Protection Area (Rio de Janeiro). Fifty-nine catfish of the three species were collected in total, along 32 collection points in the Guapi-Macacu River in two periods (dry and rainy) in 2018. Non-parametric statistics showed the partition of resources between species and the influence of abiotic factors (temperature, pH, transparency, and dissolved oxygen) contributing to the selection of available resources in the environment. Diet-related indices-repletion index (RI), condition factor (K), niche width, and trophic position (TP) of the specimens collected-contributed to measuring the nutritional status of each of these catfish species, showing that R. quelen has a relationship between RI and K, tending to absorb and metabolize nutrients faster than other species. In addition, the invasive species occupies a wide range of TPs compared to native species, confirming its feeding plasticity. On the contrary, T. striatulus needs large amounts of terrestrial insects to maintain its poor condition factor. Also, the RI showed direct influences of abiotic variables, with the temperature being the most prominent. Our results suggest that the invasive species can benefit from this environment that shows signs of environmental degradation.

Bridging macroecology and macroevolution in the radiation of sigmodontine rodents.

Investigations of phenotypic disparity across geography often ignore macroevolutionary processes. As a corollary, the random null expectations to which disparity is compared and interpreted may be unrealistic. We tackle this issue by representing, in geographical space, distinct processes of phenotypic evolution underlying ecological disparity. Under divergent natural selection, assemblages in a given region should have empirical disparity higher than expected under an evolutionarily oriented null model, whereas the opposite may indicate constraints on phenotypic evolution. We gathered phylogenies, biogeographic distributions, and data on the skull morphology of sigmodontine rodents to discover which regions of the Neotropics were more influenced by divergent, neutral, or constrained phenotypic evolution. We found that regions with higher disparity than expected by the evolutionary-oriented null model, in terms of both size and shape, were concentrated in the Atlantic Forest, suggesting a larger role for divergent natural selection there. Phenotypic disparity in the rest of South America, mainly the Amazon basin, northeastern Brazil, and Southern Andes, was constrained-lower than predicted by the evolutionary model. We also demonstrated equivalence between the disparity produced by randomization-based null models and constrained-evolution null models. Therefore, including evolutionary simulations into the null modeling framework used in ecophylogenetics can strengthen inferences on the processes underlying phenotypic evolution.

Random placement models explain species richness and dissimilarity of frog assemblages within Atlantic Forest fragments.

Understanding the effects of random versus niche-based processes on biodiversity patterns is a central theme in ecology, and an important tool for predicting effects of habitat loss and fragmentation on biodiversity. We investigated the predictive power of random processes to explain species richness and species dissimilarity of amphibian assemblages in a fragmented tropical landscape of the Atlantic Forest of South America. We analyzed a large database of amphibian abundance and occupancy, sampled in 21 forest fragments ranging in size from 1.9 to 619 ha. We compared observed species richness and species dissimilarity with the outcomes of two null (random placement) models: 1- the traditional Coleman's area-based model and 2- an abundance-based model (based on the number of individuals observed in each fragment). We applied these models for all species combined, and separately for forest-dependent and habitat-generalist species. The abundance-based model fitted the observed species richness data better than the area-based model for all species, forest-dependent species, and generalist species. The area-based and the abundance-based models were also able to significantly explain species dissimilarity for all species and for generalists, but not for forest dependent species. The traditional area-based model assigned too many individuals to large fragments, thus failing to accurately explain species richness within patches across the landscape. Although niche-based processes may be important to structuring the regional pool of species in fragmented landscapes, our results suggest that part of the variation in species richness and species dissimilarity can be successfully explained by random placement models, especially for generalist species. Evaluating which factors cause variation in the number of individuals among patches should be a focus in future studies aiming to understand biodiversity patterns in fragmented landscapes.

Compreender os efeitos de processos aleatórios versus processos baseados em nicho nos padrões de biodiversidade é um tema central em ecologia e uma ferramenta importante para prever os efeitos da perda e fragmentação de habitat na biodiversidade. Nós investigamos o poder preditivo de processos aleatórios para explicar a riqueza e a dissimilaridade de espécies de assembleias de anfíbios em uma paisagem fragmentada tropical da Mata Atlântica da América do Sul. Analisamos um grande conjunto de dados de abundância e ocupação de anfíbios, amostrados em 21 fragmentos florestais com tamanhos de 1.9 a 619 ha. Comparamos a riqueza e a dissimilaridade de espécies observadas com os resultados de dois modelos nulos (posicionamento aleatório): 1- o modelo tradicional baseado em área de Coleman e 2 - um modelo baseado em abundância (com base no número de indivíduos observados em cada fragmento). Aplicamos esses modelos para todas as espécies combinadas e separadamente para espécies dependentes de floresta e espécies generalistas de habitat. O modelo baseado em abundância ajustou-se melhor aos dados observados de riqueza de espécies do que o modelo baseado em área para todas as espécies, espécies dependentes de floresta e espécies generalistas. Os modelos baseados em área e em abundância também foram capazes de explicar significativamente a dissimilaridade de espécies para todas as espécies e para generalistas, mas não para espécies dependentes de floresta. O modelo tradicional baseado em área atribuiu muitos indivíduos a grandes fragmentos, falhando assim em explicar com precisão a riqueza de espécies dentro de manchas na paisagem. Embora processos baseados em nicho possam ser importantes para estruturar o conjunto regional de espécies em paisagens fragmentadas, nossos resultados sugerem que parte da variação na riqueza e dissimilaridade de espécies pode ser explicada com sucesso por modelos de posicionamento aleatório, especialmente para espécies generalistas. Avaliar quais fatores causam variação no número de indivíduos entre manchas deve ser um foco em estudos futuros que visem compreender os padrões de biodiversidade em paisagens fragmentadas.

Using lizards to evaluate the influence of average abundance on the variance of endoparasites in semiarid areas: dispersion and assemblage structure.

The distribution of parasites within host populations and communities, and the mechanisms responsible for these patterns, are poorly understood aspects of wildlife parasitology. Here, we evaluate the influence of the average abundance of endoparasite variance, using endoparasites of lizards from the Caatinga domain (semiarid region), north-eastern Brazil. We hypothesized that, due to the high number of generalist endoparasite species, they may occur randomly throughout host populations in an aggregate pattern. In addition, we evaluated the degree to which sample variance is influenced by the average abundance of endoparasite species, patterns of co-occurrence and dominance among endoparasite species and similarities between abundance and the richness of endoparasite infracommunities in several host species. Between September 2015 and February 2016, 2141 lizards (1233 infected) from 16 species were collected from six Caatinga areas. In total, 25,687 endoparasites were collected, which belonged to 13 species including nematodes, pentastomids, cestodes, trematodes and acanthocephalans. Parasite-host associations documented here included 39 newly identified interactions. Endoparasites occurred in a typical aggregate pattern of distribution within their hosts; there was no measurable preference related to the acquisition of hosts by endoparasites. Despite the new records, endoparasites found were commonly associated with lizards in Caatinga environments, which may reflect fauna composed of generalist endoparasite species.

Interaction frequency, network position, and the temporal persistence of interactions in a plant-pollinator network.

Ecological interactions are highly dynamic in time and space. Previous studies of plant-animal mutualistic networks have shown that the occurrence of interactions varies substantially across years. We analyzed interannual variation of a quantitative mutualistic network, in which links are weighted by interaction frequency. The network was sampled over six consecutive years, representing one of the longest time series for a community-wide mutualistic network. We estimated the interannual similarity in interactions and assessed the determinants of their persistence. The occurrence of interactions varied greatly among years, with most interactions seen in only one year (64%) and few (20%) in more than two years. This variation was associated with the frequency and position of interactions relative to the network core, so that the network consisted of a persistent core of frequent interactions and many peripheral, infrequent interactions. Null model analyses suggest that species abundances play a substantial role in generating these patterns. Our study represents an important step in the study of ecological networks, furthering our mechanistic understanding of the ecological processes driving the temporal persistence of interactions.

Herbivore exclusion promotes a more stochastic plant community assembly in a natural grassland.

Both bottom-up (e.g., nutrients) and top-down (e.g., herbivory) forces structure plant communities, but it remains unclear how they affect the relative importance of stochastic and deterministic processes in plant community assembly. Moreover, different-sized herbivores have been shown to have contrasting effects on community structure and function, but their effects on the processes governing community assembly (i.e., how they generate the impacts on structure) remain largely unknown. We evaluated the influence of bottom-up and top-down forces on the relative importance of deterministic and stochastic processes during plant community assembly. We used the data of a 7-yr factorial experiment manipulating nutrient availability (ambient and increased) and the presence of vertebrate herbivores (>1 kg) of different body size in a floodplain grassland in The Netherlands. We used a null model that describes a community composition expected by chance (i.e., stochastic assembly) and compared the plant community composition in the different treatments with this null model (the larger the difference, the more deterministically assembled). Our results showed that herbivore exclusion promoted a more stochastic plant community assembly, whereas increased nutrients played a relatively minor role in determining the relative importance of stochasticity in community assembly. Large herbivores facilitated intermediate-sized mammal herbivores, resulting in synergistic effects of enhanced grazing pressure and a more deterministic and convergent plant community assembly. We conclude that herbivores can act as strong deterministic forces during community assembly in natural systems. Our results also reveal that although large- and intermediate-sized mammal herbivores often have contrasting effects on many community and ecosystem properties, they can also synergistically homogenize plant communities.

Higher ß-diversity observed for herbs over woody plants is driven by stronger habitat filtering in a tropical understory.

Herbaceous plants are a key component of tropical forests. Previous work indicates that herbs contribute substantially to the species richness of tropical plant communities. However, the processes structuring tropical herb diversity, and how they contrast with woody communities, have been underexplored. Within the understory of a 50-ha forest dynamics plot in central Panama, we compared the diversity, distribution, and abundance of vascular herbaceous plants with woody seedlings (i.e., tree and lianas <1 cm DBH and ≥20 cm tall). Beta-diversity was calculated for each community using a null model approach. We then assessed the similarity in alpha and beta-diversity among herbs, tree seedlings, and liana seedlings. Strengths of habitat associations were measured using permutational ANOVA among topographic habitat-types. Variance partitioning was then used to quantify the amount of variation in species richness and composition explained by spatial and environmental variables (i.e., topography, soils, and shade) for each growth form. Species richness and diversity were highest for tree seedlings, followed by liana seedlings and then herbs. In contrast, beta-diversity was 16-127% higher for herbs compared to woody seedlings, indicating higher spatial variation in this stratum. We observed no correlation between local richness or compositional uniqueness of herbs and woody seedlings across sites, indicating that different processes control the spatial patterns of woody and herbaceous diversity and composition. Habitat associations were strongest for herbs, as indicated by greater compositional dissimilarity among habitat types. Likewise, environmental variables explained a larger proportion of the variation in species richness and composition for herbs than for woody seedlings (richness = 25%, 14%, 12%; composition = 25%, 9%, 6%, for herbs, trees, and lianas, respectively). These differences between strata did not appear to be due to differences in lifespan alone, based on data from adult trees. Our results point to contrasting assembly mechanisms for herbaceous and woody communities, with herbs showing stronger niche-derived structure. Future research on tropical herbaceous communities is likely to yield new insights into the many processes structuring diverse plant communities.

Nestedness patterns of sand fly (Diptera: Psychodidae) species in a neotropical semi-arid environment.

A common pattern in neotropical Leishmania spp. transmission is the co-occurrence of several sand fly (SF) species at endemic foci. We collected 13 SF spp. by direct aspiration in natural resting places (NRP) and 10 SF spp. with Shannon traps (ST), totaling 15 spp. with both methods, at 6 locations within a semi-arid region with endemic visceral leishmaniasis transmission in Falcón State, Northwestern Venezuela. We used null model testing of species co-occurrence and nestedness metrics estimated with our field data to ask whether SF species composition was segregated/aggregated, and if aggregated whether there was nestedness, i.e., whether species composition across sampling locations could be described by ordered subsets of species from the most species rich location in a landscape. Results showed that SF species were aggregated (P<0.05), i.e., most species were present in species rich locations. Similarly, SF species were significantly nested (P<0.05). Differences in pairwise Sørensen and Simpson indices, estimated with the ST data and the combined ST and NRP data, were positively associated with the distance between sampling locations, suggesting that species nestedness might be partially shaped by dispersal limitation. Our data showed that three species of medical importance were common across the sampling locations: Lutzomyia gomezi, Lutzomyia panamensis and Lutzomyia evansi, suporting that vector species do not turnover in the studied setting.

Edge effects and geometric constraints: a landscape-level empirical test.

Edge effects are pervasive in landscapes yet their causal mechanisms are still poorly understood. Traditionally, edge effects have been attributed to differences in habitat quality along the edge-interior gradient of habitat patches, under the assumption that no edge effects would occur if habitat quality was uniform. This assumption was questioned recently after the recognition that geometric constraints tend to reduce population abundances near the edges of habitat patches, the so-called geometric edge effect (GEE). Here, we present the first empirical, landscape-level evaluation of the importance of the GEE in shaping abundance patterns in fragmented landscapes. Using a data set on the distribution of small mammals across 18 forest fragments, we assessed whether the incorporation of the GEE into the analysis changes the interpretation of edge effects and the degree to which predictions based on the GEE match observed responses. Quantitative predictions were generated for each fragment using simulations that took into account home range, density and matrix use for each species. The incorporation of the GEE into the analysis changed substantially the interpretation of overall observed edge responses at the landscape scale. Observed abundances alone would lead to the conclusion that the small mammals as a group have no consistent preference for forest edges or interiors and that the black-eared opossum Didelphis aurita (a numerically dominant species in the community) has on average a preference for forest interiors. In contrast, incorporation of the GEE suggested that the small mammal community as a whole has a preference for forest edges, whereas D. aurita has no preference for forest edges or interiors. Unexplained variance in edge responses was reduced by the incorporation of GEE, but remained large, varying greatly on a fragment-by-fragment basis. This study demonstrates how to model and incorporate the GEE in analyses of edge effects and that this incorporation is necessary to properly interpret edge effects in landscapes. It also suggests that geometric constraints alone are unlikely to explain the variability in edge responses of a same species among different areas, highlighting the need to incorporate other ecological factors into explanatory models of edge effects.

A new dynamic null model for phylogenetic community structure.

Phylogenies are increasingly applied to identify the mechanisms structuring ecological communities but progress has been hindered by a reliance on statistical null models that ignore the historical process of community assembly. Here, we address this, and develop a dynamic null model of assembly by allopatric speciation, colonisation and local extinction. Incorporating these processes fundamentally alters the structure of communities expected due to chance, with speciation leading to phylogenetic overdispersion compared to a classical statistical null model assuming equal probabilities of community membership. Applying this method to bird and primate communities in South America we show that patterns of phylogenetic overdispersion - often attributed to negative biotic interactions - are instead consistent with a species neutral model of allopatric speciation, colonisation and local extinction. Our findings provide a new null expectation for phylogenetic community patterns and highlight the importance of explicitly accounting for the dynamic history of assembly when testing the mechanisms governing community structure.

An integrated framework to improve the concept of resource specialisation.

Resource specialisation, although a fundamental component of ecological theory, is employed in disparate ways. Most definitions derive from simple counts of resource species. We build on recent advances in ecophylogenetics and null model analysis to propose a concept of specialisation that comprises affinities among resources as well as their co-occurrence with consumers. In the distance-based specialisation index (DSI), specialisation is measured as relatedness (phylogenetic or otherwise) of resources, scaled by the null expectation of random use of locally available resources. Thus, specialists use significantly clustered sets of resources, whereas generalists use over-dispersed resources. Intermediate species are classed as indiscriminate consumers. The effectiveness of this approach was assessed with differentially restricted null models, applied to a data set of 168 herbivorous insect species and their hosts. Incorporation of plant relatedness and relative abundance greatly improved specialisation measures compared to taxon counts or simpler null models, which overestimate the fraction of specialists, a problem compounded by insufficient sampling effort. This framework disambiguates the concept of specialisation with an explicit measure applicable to any mode of affinity among resource classes, and is also linked to ecological and evolutionary processes. This will enable a more rigorous deployment of ecological specialisation in empirical and theoretical studies.

A comparison of computer-generated and naturally occurring foraging patterns in route-network-constrained spider monkeys.

The attribution of goal-directed behavior to observations of primate foraging and ranging requires that simpler explanations for observed behavior patterns be eliminated. Computer-generated simulations of non-goal-directed foraging behavior can be used as null models for higher complexity cognitive foraging, and can provide quantifiable data against which to compare the observed behavioral patterns in wild primates. In this paper, we compare the results of two variations of computer simulated null models with observed foraging behavior of wild spider monkeys (Ateles belzebuth). One model simulates monkeys searching using a modified random-walk model in which monkeys alternate 100-m steps with turn angles derived from observed behavior. The second model constrains travel to an observed route system derived from observations of wild spider monkeys. Simulated monkeys in each model searched among increasing densities of feeding trees ranging from 10 to 1,000. We compared travel distance, travel directness, and accuracy of starting direction for each feeding tree discovered for the two models. We then compared these results with those derived from observations of wild spider monkeys. Route-model monkeys traveled shorter distances and more directly to feeding trees than did randomly foraging monkeys, and discovered trees in the direction they started more often. Observed spider monkeys outperformed simulated monkeys from both models in all variables, allowing us to reject the null hypothesis that observed foraging and ranging behavior could be explained by non-goal-directed travel.

Bird species diversity in the Atlantic Forest of Brazil is not explained by the Mid-domain Effect

The Atlantic Forest is an excellent case study for the elevational diversity of birds, and some inventories along elevational gradients have been carried out in Brazil. Since none of these studies explain the patterns of species richness with elevation, we herein review all Brazilian studies on bird elevational diversity, and test a geometric constraint null model that predicts a unimodal species-altitude curve, the Mid-domain Effect (MDE). We searched for bird inventories in the literature and also analysed our own survey data using limited-radius point counts along an 800 m elevational gradient in the state of São Paulo, Brazil. We found 10 investigations of elevational diversity of Atlantic Forest birds and identified five different elevational patterns: monotonic decreasing diversity, constant at low elevations, constant at low elevations but increasing towards the middle, and two undescribed patterns for Atlantic Forest birds, trough-shaped and increasing diversity. The average MDE fit was low (r² = 0.31) and none of the MDE predictions were robust across all gradients. Those studies with good MDE model fits had obvious sampling bias. Although it has been proposed that the MDE may be positively associated with the elevational diversity of birds, it does not fit the Brazilian Atlantic Forest bird elevational diversity.

Bird species diversity in the Atlantic Forest of Brazil is not explained by the Mid-domain Effect

The Atlantic Forest is an excellent case study for the elevational diversity of birds, and some inventories along elevational gradients have been carried out in Brazil. Since none of these studies explain the patterns of species richness with elevation, we herein review all Brazilian studies on bird elevational diversity, and test a geometric constraint null model that predicts a unimodal species-altitude curve, the Mid-domain Effect (MDE). We searched for bird inventories in the literature and also analysed our own survey data using limited-radius point counts along an 800 m elevational gradient in the state of São Paulo, Brazil. We found 10 investigations of elevational diversity of Atlantic Forest birds and identified five different elevational patterns: monotonic decreasing diversity, constant at low elevations, constant at low elevations but increasing towards the middle, and two undescribed patterns for Atlantic Forest birds, trough-shaped and increasing diversity. The average MDE fit was low (r² = 0.31) and none of the MDE predictions were robust across all gradients. Those studies with good MDE model fits had obvious sampling bias. Although it has been proposed that the MDE may be positively associated with the elevational diversity of birds, it does not fit the Brazilian Atlantic Forest bird elevational diversity.

Bird species diversity in the Atlantic Forest of Brazil is not explained by the Mid-domain Effect

The Atlantic Forest is an excellent case study for the elevational diversity of birds, and some inventories along elevational gradients have been carried out in Brazil. Since none of these studies explain the patterns of species richness with elevation, we herein review all Brazilian studies on bird elevational diversity, and test a geometric constraint null model that predicts a unimodal species-altitude curve, the Mid-domain Effect (MDE). We searched for bird inventories in the literature and also analysed our own survey data using limited-radius point counts along an 800 m elevational gradient in the state of São Paulo, Brazil. We found 10 investigations of elevational diversity of Atlantic Forest birds and identified five different elevational patterns: monotonic decreasing diversity, constant at low elevations, constant at low elevations but increasing towards the middle, and two undescribed patterns for Atlantic Forest birds, trough-shaped and increasing diversity. The average MDE fit was low (r² = 0.31) and none of the MDE predictions were robust across all gradients. Those studies with good MDE model fits had obvious sampling bias. Although it has been proposed that the MDE may be positively associated with the elevational diversity of birds, it does not fit the Brazilian Atlantic Forest bird elevational diversity.

Assembly rules in Muscid Fly assemblages in the grasslands Biome of Southern Brazil

The distribution of muscid species (Diptera) in grasslands fragments of southern Brazil was assessed using null models according to three assembly rules: (a) negatively-associated distributions; (b) guild proportionality; and (c) constant body-size ratios. We built presence/absence matrices and calculated the C-score index to test negatively-associated distributions and guild proportionality based on the following algorithms: total number of fixed lines (F L), total number of fi xed columns (F C), and the effect of the average size of the populations along lines (W) for 5000 randomizations. We used null models to generate random communities that were not structured by competition and evaluated the patterns generated using three models: general, trophic guilds, and taxonomic guilds. All three assembly rules were tested in each model. The null hypothesis was corroborated in all F L X F C co-occurrence analyses. In addition, 11 analyses of the models using the W algorithm showed the same pattern observed previously. Three analyses using the W algorithm indicated that species co-occurred more frequently than expected by chance. According to analyses of co-occurrence and guild proportionality, the coexistence of muscid species is not regulated by constant body size ratios. In fl ies of the grasslands, no rule was identified. Yet, a consensus did emerge from our analyses: species co-occur more frequently than expected by chance, indicating that aggregation is a recurring phenomenon among flies with saprophagous adults and predatory larvae. Therefore, competition does not seem to play an important role in the determination of muscid assemblages in the grasslands in Southern Brazil.

Species assemblages of zooplanktonic crustaceans in mountain shallow ponds of Chile (Parque Cañi)

Even though the Chilean lakes are characterized by their oligotrophy, a transition from oligotrophy to mesotrophy, due human intervention, has been reported in some lakes. Nevertheless, there are still some pristine and unpolluted small lakes and ponds in mountain zones, free of human intervention and surrounded by native forests. Nine unpolluted, oligotrophic and pristine water bodies located in Cañi Park, a mountain zone with altitudes between 1000 to 1500 m a.s.l and forests where Nothofagus dombeyi, N. pumilio and Araucaria araucana predominate, were studied. For each sampled lake, zooplankton was collected and environmental parameters were obtained (conductivity, total dissolved solids, and chlorophyll concentration). A null model of species co-occurrence was applied to determine randomness in species associations. All sites revealed low species richness ( 6); the calanoid copepod Boeckella gracilis Daday, 1902 was present in all sites. The results of the null model indicated randomness or absence of regulatory factors in species associations. Only few species occur in practically all localities. Also, a significant inverse association between chlorophyll concentration with percentage of calanoid copepods and a weak direct association between chlorophyll concentration and percentages of cladocerans were found.

Species assemblages of zooplanktonic crustaceans in mountain shallow ponds of Chile (Parque Cañi)

Even though the Chilean lakes are characterized by their oligotrophy, a transition from oligotrophy to mesotrophy, due human intervention, has been reported in some lakes. Nevertheless, there are still some pristine and unpolluted small lakes and ponds in mountain zones, free of human intervention and surrounded by native forests. Nine unpolluted, oligotrophic and pristine water bodies located in Cañi Park, a mountain zone with altitudes between 1000 to 1500 m a.s.l and forests where Nothofagus dombeyi, N. pumilio and Araucaria araucana predominate, were studied. For each sampled lake, zooplankton was collected and environmental parameters were obtained (conductivity, total dissolved solids, and chlorophyll concentration). A null model of species co-occurrence was applied to determine randomness in species associations. All sites revealed low species richness ( 6); the calanoid copepod Boeckella gracilis Daday, 1902 was present in all sites. The results of the null model indicated randomness or absence of regulatory factors in species associations. Only few species occur in practically all localities. Also, a significant inverse association between chlorophyll concentration with percentage of calanoid copepods and a weak direct association between chlorophyll concentration and percentages of cladocerans were found.

Species assemblages of zooplanktonic crustaceans in mountain shallow ponds of Chile (Parque Cañi)

Even though the Chilean lakes are characterized by their oligotrophy, a transition from oligotrophy to mesotrophy, due human intervention, has been reported in some lakes. Nevertheless, there are still some pristine and unpolluted small lakes and ponds in mountain zones, free of human intervention and surrounded by native forests. Nine unpolluted, oligotrophic and pristine water bodies located in Cañi Park, a mountain zone with altitudes between 1000 to 1500 m a.s.l and forests where Nothofagus dombeyi, N. pumilio and Araucaria araucana predominate, were studied. For each sampled lake, zooplankton was collected and environmental parameters were obtained (conductivity, total dissolved solids, and chlorophyll concentration). A null model of species co-occurrence was applied to determine randomness in species associations. All sites revealed low species richness ( 6); the calanoid copepod Boeckella gracilis Daday, 1902 was present in all sites. The results of the null model indicated randomness or absence of regulatory factors in species associations. Only few species occur in practically all localities. Also, a significant inverse association between chlorophyll concentration with percentage of calanoid copepods and a weak direct association between chlorophyll concentration and percentages of cladocerans were found.