Do larvae of species in macrolepidopteran assemblages share traits that influence susceptibility to parasitism?

Research on how morphology, behavior, and life histories of insects determine their susceptibility to parasitism has primarily focused on the traits of single host species. Very little research has been conducted attempting to determine if similarities or differences in the traits of co-occurring species, on a single plant or in a habitat, influence levels of parasitism imposed on any member of an assemblage. In this study, we use categorical and regression tree analyses to determine which traits of the larvae of macrolepidopteran species are associated with highest levels of parasitism. Of a variety of morphological, behavioral, and ecological traits of 72 species (representing eight families), caterpillar color was the trait that had the greatest influence on susceptibility to parasitism. The highest levels of parasitism were associated primarily with green larvae. These results suggest that the herbivore species composition and, specifically, the traits possessed by the species may influence community or assemblagewide patterns of parasitism. That is, sharing of traits that enhance host finding and successful parasitism may result in associational susceptibility to parasitism, whereas co-occurrence with species that differ morphologically, behaviorally, or ecologically may reduce the likelihood of parasitism and thus result in associational resistance. The concepts of associational resistance and susceptibility have historically been restricted to plant-plant interactions. The extension of these concepts to herbivores is novel. If found to be widespread, these interactions can have significant impacts on our expectations of the effectiveness of biological control agents.     

Top predator fish assemblages in Northern Patagonia,Argentina. What factors regulate their patterns of distribution and abundance?

According to assemblage theory, three factors regulate fish biogeography: restriction of dispersion, environmental restrictions and biotic interactions. The first two factors act on a regional scale and delimit the area of action of the third, which operates on a local scale. Salmonid introductions began in Patagonia in 1904, and this has led to a restructuring of trophic webs and an increase in the number of top predators. This situation allowed us to evaluate, in a natural setting, how communities are formed on different geographic scales. We studied two large basins in Patagonia, situated close to each other but with different assemblages of top predatory fish. We hypothesized that differences in the structuring of the top predator assemblages between and within the basins are due to 1) environmental factors and dispersion processes facilitated by connectivity on a regional scale; and 2) biotic interaction (internal dynamics) between native perch and salmonids, the former acting as a modulator of the top predator assemblages on a local scale. To test these hypotheses, we analysed the top predator assemblages of 16 lakes and one reservoir, as well as their environmental characteristics. We performed a cluster analysis and related the resulting assembly groups to environmental factors by means of a tree model. We also analysed fish diets, using a similarities test to study biotic interactions. On regional and local scales, water basin, degree of connectivity, area, temperature and Zoogeographic integrity coefficient (ZIC) were important factors in the structuring of top predator assemblages. On a local scale, creole perch modulates the salmonid populations through feeding and the consequent distribution of resources. Our work showed that the structure of top predator assemblages was determined by a combination of local and regional factors acting in synergy, as postulated by the assemblage theory.     

Is there an ecological basis for species abundance distributions?

Community ecologists have attempted to explain species abundance distribution (SAD) shape for more than 80 years, but usually without relating SAD shape explicitly to ecological variables. We explored whether the scale (total assemblage abundance) and shape (assemblage evenness) of avifaunal SADs were related to ecological covariates. We used data on avifaunas, in-site habitat structure and landscape context that were assembled from previous studies; this amounted to 197 transects distributed across 16,000 km² of the box-ironbark forests of southeastern Australia. We used Bayesian conditional autoregressive models to link SAD scale and shape to these ecological covariates. Variation in SAD scale was relatable to some ecological covariates, especially to landscape vegetation cover and to tree height. We could not find any relationships between SAD shape and ecological covariates. SAD shape, the core component in SAD theory, may hold little information about how assemblages are governed ecologically and may result from statistical processes, which, if general, would indicate that SAD shape is not useful for distinguishing among theories of assemblage structure.     

Do species of invaded communities differ in their vulnerability to being eliminated by the dominant alien plants?

Invasions are associated with loss of diversity and changes in species composition. This study aims to provide evidence if this loss happens at random or if the loss is related to functional traits of native species. Traits of species in communities dominated by 13 plants alien to Central Europe were compared to those found in the adjacent uninvaded vegetation. There is a weak but significant non-random pattern in the distribution of traits between the invaded and adjacent uninvaded vegetation. For example, species possessing a taproot, annuals but also juveniles of trees tend to be proportionally more abundant in the invaded vegetation, suggesting they are impacted less than species with high clonal index, perennial polycarpic species and species without a taproot, which are proportionally more represented in the uninvaded vegetation. Fast laterally spreading species, trees’ juveniles and woody species in general are proportionally more frequent in the invaded vegetation, while biennials, slow laterally spreading species but also shrubs are proportionally more frequent in the uninvaded vegetation. Juveniles of trees may compete successfully with the aliens due to being adapted to thrive in low light conditions. Annuals may thrive in the invaded communities by possessing a life strategy different from most of the selected aliens. Possessing a taproot appears to be another trait important for the successful coexistence with the dominant invasive aliens, possibly pointing to the importance of underground competition. Clonal perennial polycarpic herbs are species functionally most similar to most of the selected aliens, and these species were found to be most underrepresented in the invaded vegetation.     

Is the abundance of species determined by their functional traits? A new method with a test using plant communities

The relation between functional traits and abundance of species has the potential to provide evidence on the mechanisms that structure local ecological communities. The niche-limitation/limiting-similarity hypothesis, derived from MacArthur and Levins’ original concept, predicts that species that are similar to others in terms of functional traits will suffer greater competition and hence be less abundant. On the other hand, the environment-filtering/habitat-optimum hypothesis predicts that groups of species with functional traits that are close to the optimum for that environment, and are therefore similar to other species, will be more abundant. We propose a new niche-assembly model for predicting the relative abundance of species in communities from their functional traits, which can detect the patterns that would be expected from either of these hypotheses. The model was fitted to eight plant communities sampled in the Lake Ohau district of New Zealand. For seven of the sites, the patterns could not be distinguished from that expected under a null model. However, in one site there was highly significant departure from the null model in the direction expected from the niche-limitation hypothesis. The site was probably the most productive of those examined. It is possible that competition for light rather than belowground resources, or faster recovery from disturbance, allowed greater predictability. Surprisingly, the predictability was seen when just the presences of a species’ neighbours in trait space were taken into account, but not when the potential effects of those neighbours were weighted by their abundance. For three of the four model types, the effects of species on each other were consistently negative: a significant trend. These results contradict the various neutral models of ecological communities.     

Is abundance a species attribute? An example with haematophagous ectoparasites

Population density is a fundamental property of a species and yet it varies among populations of the same species. The variation comes from the interplay between intrinsic features of a species that tend to produce repeatable density values across all populations of the same species and extrinsic environmental factors that differ among localities and thus tend to produce spatial variation in density. Is inter-population variation in density too large for density to be considered a true species character? We addressed this question using data on abundance (number of parasites per individual host, i.e. equivalent to density) of fleas ectoparasitic on small mammals. The data included samples of 548 flea populations, representing 145 flea species and obtained from 48 different geographical regions. Abundances of the same flea species on the same host species, but in different regions, were more similar to each other than expected by chance, and varied significantly among flea species, with 46% of the variation among samples accounted by differences between flea species. Thus, estimates of abundance are repeatable within the same flea species. The same repeatability was also observed, but to a lesser extent, across flea genera, tribes and subfamilies. Independently of the identity of the flea species, abundance values recorded on the same host species, or in the same geographical region, also showed significant statistical repeatability, though not nearly as strong as that associated with abundance values from the same flea species. There were also no strong indications that regional differences in abiotic variables were an important determinant of variation in abundance of a given flea species on a given host species. Abundance thus appears to be a true species trait in fleas, although it varies somewhat within bounds set by species-specific life history traits.     

Is orchid species richness and abundance related to the conservation status of oak forest?

The response of organisms to anthropogenic or natural modification of the environment is one of the most important questions in conservation biology and ecological theory. In spite of the fact that orchids are one of the most studied groups of plants, little information exists regarding their response to habitat alteration. The few existing studies are biased toward European orchid species and no consensus exists with regard to the response of orchids to human and natural disturbance. In this study, we sampled 30 transects (0.1 ha each) of oak forest located in Morelos, Central Mexico, and measured 13 variables related to forest aging and stump abundance, and six variables of orchid species richness and abundance. Neither abundance nor the richness and specific abundance of orchid genus or species were related to timber extraction. The abundance of dead standing trees in the forest, a surrogate variable of forest age, was positively related to abundance of orchids of the genus Malaxis, orchid richness and orchid abundance. This finding suggests that the conservation of all facets of the studied forest orchid community is dependent on natural processes (such as self-thinning) and the maintenance of older areas of the forest, and concurs with previous studies that suggest that natural disturbance is a key process for orchid survival.     

Is evenness altered by fire in natural assemblages of soil arthropods?

We studied evenness and species richness in two assemblages of soil arthropods at six contiguous study plots in Mediterranean ecosystems of central Italy, three of these plots being burnt and three unburnt. We analysed these aspects of community structure by diversity–dominance diagrams comparisons made through analysis of covariance on respective slopes and ordinate intercepts. We observed consistent patterns in both Collembola and Oniscidea assemblages, either in burnt and unburnt plots. Evenness did not change among study plots and across habitats, either before or after fire, whereas species' composition was significantly altered by fire. Results from our study implied that evenness and species diversity are clearly affected in a different and independent way by fire. Hence, it is not acceptable to focus on only the evenness when looking at the effects of controlled fires for environmental management reasons.     

Why do species vary in their rate of molecular evolution?

Despite hopes that the processes of molecular evolution would be simple, clock-like and essentially universal, variation in the rate of molecular evolution is manifest at all levels of biological organization. Furthermore, it has become clear that rate variation has a systematic component: rate of molecular evolution can vary consistently with species body size, population dynamics, lifestyle and location. This suggests that the rate of molecular evolution should be considered part of life-history variation between species, which must be taken into account when interpreting DNA sequence differences between lineages. Uncovering the causes and correlates of rate variation may allow the development of new biologically motivated models of molecular evolution that may improve bioinformatic and phylogenetic analyses.     

Conservation targets for viable species assemblages?

Estimates of minimum areas required for effective biodiversity conservation differ substantially. Scientific reserve design and placement procedures indicate that between 30 and 75% of any region may be required to sample biodiversity features. These estimates do not routinely incorporate measures for sampling viable populations of species or explore the area requirements of sampling viable populations of species assemblages. To determine the area requirements for sampling viable populations of a herbivore assemblage, spatially explicit abundance data from the Kruger National Park, South Africa, were analyzed. Area requirements were consistently above 50% and were unaffected by selected target population sizes. In addition, area requirements appeared to be insensitive to selection unit size (analytical grain), habitat quality, the coarseness of the land classification system used or the presence of low-density species. Thus, traditional conservation area targets of 10–15% appear inadequate for representing viable populations of a herbivore assemblage from African savanna regions. This suggests that conservation targets of at least 50% of land classification units may represent a more appropriate conservation rule of thumb, or alternatively, that the use of data independent conservation targets may need to be abandoned.     

Is parasitism of metazoa “a one-way ticket”?

Various phenomena interpreted as possible cases of metazoans returning from obligate parasitism to the free-living state (a violation of the ecological interpretation of Dollo’s law) are critically considered. It is shown that among temporary and phase parasites, reversal to the free-living state is a very rare but not exceptional phenomenon. Such cases occur only among the temporary ectoparasites whose ancestors were predators. The only case of violation of Dollo’s law among permanent parasites, although an incompletely proved one, was detected in acariform mites of the family Pyroglyphidae (Acariformes: Psoroptoidea).     

Is Aeromonas hydrophila the dominant motile Aeromonas species that causes disease outbreaks in aquaculture production in the Zhejiang Province of China?

The significance of Aeromonas hydrophila in association with disease outbreaks in aquaculture production in the Zhejiang province of China was investigated. Bacteriological examination of moribund fish and crabs resulted in 95 bacterial isolates: 88 bacterial isolates from fish and 7 isolates from crabs. PCR and traditional biochemical methods were used for identification of A. hydrophila. Out of 69 motile aeromonads, 35 isolates were identified as A. hydrophila by biochemical tests. However, 6 of those were not identified as A. hydrophila by a species specific PCR method. Serotyping revealed 2 dominant serotypes (O9 and O97) among A. hydrophila isolates. The data presented show that approximately 42% of the motile aeromonads isolated from disease outbreaks among various fish species were A. hydrophila. It is noteworthy that A. hydrophila accounted for more than 50% of the isolated aeromonands isolated from crucian carp Carassius carassius and Wuchang bream Megalobrama amblycephala with haemorrhagic septicaemia. Although this species was the most frequently isolated organism from internal organs of diseased fish and crabs in the present study, other motile Aeromonas spp. were also found. The PCR assay was useful in preventing misidentification of A. hydrophila, which may occur when only phenotypic tests are employed.     

How does variation in total and relative abundance contribute to gradients of species diversity?

Patterns of biodiversity provide insights into the processes that shape biological communities around the world. Variation in species diversity along biogeographical or ecological gradients, such as latitude or precipitation, can be attributed to variation in different components of biodiversity: changes in the total abundance (i.e., more‐individual effects) and changes in the regional species abundance distribution (SAD). Rarefaction curves can provide a tool to partition these sources of variation on diversity, but first must be converted to a common unit of measurement. Here, we partition species diversity gradients into components of the SAD and abundance using the effective number of species (ENS) transformation of the individual‐based rarefaction curve. Because the ENS curve is unconstrained by sample size, it can act as a standardized unit of measurement when comparing effect sizes among different components of biodiversity change. We illustrate the utility of the approach using two data sets spanning latitudinal diversity gradients in trees and marine reef fish and find contrasting results. Whereas the diversity gradient of fish was mostly associated with variation in abundance (86%), the tree diversity gradient was mostly associated with variation in the SAD (59%). These results suggest that local fish diversity may be limited by energy through the more‐individuals effect, while species pool effects are the larger determinant of tree diversity. We suggest that the framework of the ENS‐curve has the potential to quantify the underlying factors influencing most aspects of diversity change.     

Is vascular plant species diversity a predictor of bryophyte species diversity in Mediterranean forests?

This study aimed to (i) investigate the congruence among the species composition and diversity of bryophytes and vascular plants in forests; (ii) test if site prioritization for conservation aims by the maximization of the pooled number of vascular plant species is effective to maximize the pooled number of bryophyte species. The study was performed in six forests in Tuscany, Italy. Four-hundred and twenty vascular plant species (61 of which were woody) and 128 bryophyte species were recorded in 109 plots. Despite the good predictive value of the compositional patterns of both woody plants and total vascular with respect to the compositional pattern of bryophytes, the species richness of the latter was only marginally related to the species richness of the former two. Bryophyte rare species were not spatially related to rare plant species and neither coincided with the sites of highest plant species richness. The species accumulation curves of bryophytes behaved differently with respect to those of woody plants or total vascular plants. Reserve selection analysis based on the maximization of the pooled species richness of either woody plants or total vascular plants were not effective in maximizing the pooled species richness of bryophytes. This study indicates that species diversity of vascular plants is not likely to be a good indicator of the bryophyte species diversity in Mediterranean forests.     

Evaluating detectability of freshwater fish assemblages in tropical streams: Is hand-seining sufficient?

Unprecedented threats to natural ecosystems mean that accurate quantification of biodiversity is a priority, particularly in the tropics which are underrepresented in monitoring schemes. Data from a freshwater fish assemblage in Trinidad were used to evaluate the effectiveness of hand-seining as a survey method in tropical streams. We uncovered large differences in species detectability when hand-seining was used alone, in comparison with when hand-seining and electrofishing were used together. The addition of electrofishing increased the number of individuals caught threefold, and increased the biomass fivefold. Some species were never detected using hand-seining, resulting in significant underestimates of species richness; rarefaction curves suggest that even when hand-seining effort increases, species richness is still underestimated. Diversity indices (Shannon and Simpson index) reveal that diversity was also significantly lower for hand-seined samples. Furthermore, the results of multivariate analyses investigating assemblage structure also differed significantly depending on whether they were based on hand-seined data alone, or a combination of hand-seining and electrofishing. Despite the extra equipment and maintenance required, these findings underline the value of including electrofishing when sampling tropical freshwater streams.     

Do generalized scaling laws exist for species abundance distribution in mountains?

Knowing the global pattern of species diversity is a central goal of the science of ecology, and scaling laws can be useful for analysis of cross-scale biodiversity patterns. An elevational gradient in a warm temperate zone of the Donglingshan mountains (China) is used to test the scaling laws of species abundance distribution using multifractal analysis. We show that the power law scaling relationship holds for not just the classical SAR (species–area relationship for richness), but also for Shannon and Simpson diversity. In fact, we find power-laws in the generalized species abundance distribution at all stratal levels of the forest (trees, shrubs and herbs). The fact that these laws exist across a heterogeneous landscape representing a strong bioclimatic gradient suggests that biodiversity scaling laws may be more robust than previously thought.