Species richness is a fundamental measurement of community and regional diversity, and it underlies many ecological models and conservation strategies. In spite of its importance, ecologists have not always appreciated the effects of abundance and sampling effort on richness measures and comparisons. We survey a series of common pitfalls in quantifying and comparing taxon richness. These pitfalls can be largely avoided by using accumulation and rarefaction curves, which may be based on either individuals or samples. These taxon sampling curves contain the basic information for valid richness comparisons, including category‐subcategory ratios (species-to-genus and species-toindividual ratios). Rarefaction methods ‐ both sample-based and individual-based ‐ allow for meaningful standardization and comparison of datasets. Standardizing data sets by area or sampling effort may produce very different results compared to standardizing by number of individuals collected, and it is not always clear which measure of diversity is more appropriate. Asymptotic richness estimators provide lower-bound estimates for taxon-rich groups such as tropical arthropods, in which observed richness rarely reaches an asymptote, despite intensive sampling. Recent examples of diversity studies of tropical trees, stream invertebrates, and herbaceous plants emphasize the importance of carefully quantifying species richness using taxon sampling curves.

/pdf/quantifying-biodiversity-procedures-and-pitfalls-in-the-2ut2f3nw4g.pdf

Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness

Although the effects of invasive alien species (IAS) on native species are well documented, the many ways in which such species impact ecosystem services are still emerging. Here we assess the costs and benefits of IAS for provisioning, regulating and cultural services, and illustrate the synergies and tradeoffs associated with these impacts using case studies that include South Africa, the Great Lakes and Hawaii. We identify services and interactions that are the least understood and propose a research and policy framework for filling the remaining knowledge gaps. Drawing on ecology and economics to incorporate the impacts of IAS on ecosystem services into decision making is key to restoring and sustaining those life-support services that nature provides and all organisms depend upon.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(09)00176-1.pdf

Invasive species, ecosystem services and human well-being.

Marine microbial communities are engines of globally important processes, such as the marine carbon, nitrogen and sulphur cycles. Recent data on the structures of these communities show that they adhere to universal biological rules. Co-occurrence patterns can help define species identities, and systems-biology tools are revealing networks of interacting microorganisms. Some microbial systems are found to change predictably, helping us to anticipate how microbial communities and their activities will shift in a changing world.

/pdf/microbial-community-structure-and-its-functional-3mrgmclufe.pdf

Microbial community structure and its functional implications

/pdf/an-introduction-to-the-aquatic-insects-of-north-america-20i7stzjkw.pdf

An Introduction to the Aquatic Insects of North America

We describe here the ecological and evolutionary processes that modulate the effects of invasive species over time, and argue that such processes are so widespread and important that ecologists should adopt a long-term perspective on the effects of invasive species. These processes (including evolution, shifts in species composition, accumulation of materials and interactions with abiotic variables) can increase, decrease, or qualitatively change the impacts of an invader through time. However, most studies of the effects of invasive species have been brief and lack a temporal context; 40% of recent studies did not even state the amount of time that had passed since the invasion. Ecologists need theory and empirical data to enable prediction, understanding and management of the acute and chronic effects of species invasions.

/pdf/understanding-the-long-term-effects-of-species-invasions-2o20y8wczj.pdf

Understanding the long-term effects of species invasions.

J. M. Diamond's assembly rules model predicts that competitive interactions between species lead to nonrandom co-occurrence patterns. We conducted a meta-analysis of 96 published presence–absence matrices and used a realistic “null model” to generate patterns expected in the absence of species interactions. Published matrices were highly nonrandom and matched the predictions of Diamond's model: there were fewer species combinations, more checkerboard species pairs, and less co-occurrence in real matrices than expected by chance. Moreover, nonrandom structure was greater in homeotherm vs. poikilotherm matrices. Although these analyses do not confirm the mechanisms of Diamond's controversial assembly rules model, they do establish that observed co-occurrence in most natural communities is usually less than expected by chance. These results contrast with previous analyses of species co-occurrence patterns and bridge the apparent gap between experimental and correlative studies in community ecology.

/pdf/species-co-occurrence-a-meta-analysis-of-j-m-diamond-s-30nul58uk2.pdf

Species co-occurrence: a meta-analysis of j. m. diamond's assembly rules model

Disturbance frequency, intensity, and areal extent may influence the effects of disturbance on biological communities. Furthermore, these three factors may have interacting effects on biological diversity. We manipulated the frequency, intensity, and area of disturbance in a full-factorial design on artificial substrates and measured responses of benthic macroinvertebrates in a northern Vermont stream. Macroinvertebrate abundance was lower in all disturbance treatments than in the undisturbed control. As in most other studies in streams, species density (number of species/sample) was lower in disturbed treatments than in undisturbed controls. However, species density is very sensitive to total abundance of a sample, which is usually reduced by disturbance. We used a rarefaction method to compare species richness based on an equivalent number of individuals. In rarefied samples, species richness was higher in all eight disturbed treatments than in the undisturbed control, with significant increases in species richness for larger areas and greater intensities of disturbance. Increases in species richness in response to disturbance were consistent within patches, among patches with similar disturbance histories, and among patches with differing disturbance histories. These results provide some support for Huston’s dynamic-equilibrium model but do not support the intermediate-disturbance hypothesis. Our analyses demonstrate that species richness and species density can generate opposite patterns of community response to disturbance. The interplay of abundance, species richness, and species density has been neglected in previous tests of disturbance models.

Effects of disturbance frequency, intensity, and area on assemblages of stream macroinvertebrates

Adult zebra mussels are generally thought of as sessile animals. However, when detached from their byssus, adult mussels exhibit creeping behavior similar to that of other bivalve species. Our study examined the effects of size, light, water hardness, temperature, and the presence of injured conspecifics on the movement of adult zebra mussels. Mussels were placed in aquaria and their movement was recorded after a 2-h interval. Mussels left visible trails in a thin layer of sand on the aquarium floor that allowed for accurate measurements of distance and direction of movement. The tendency to move and distance moved by the mussels was inversely proportional to size of the individual mussels. There was no significant effect of temperature on movement, though smaller mussels tended to move more at higher temperatures. Although distance traveled was not significantly different in light versus dark conditions, there was a significant effect of light on direction traveled. Zebra mussels were strongly ne...

Factors affecting the movement of adult zebra mussels (Dreissena polymorpha)

Summary

1. We examined the effect of zebra mussel colonisation on invertebrate communities inhabiting soft sediments in two bays along the Vermont shoreline of Lake Champlain, U.S.A.



2. In summer 2001, we conducted manipulative experiments (addition and removal of zebra mussel colonies) with respective controls to assess the effect of colonies on invertebrate abundance, richness, and position within sediments (within colony versus underlying colony) and compared these data to comparative studies of natural communities in summer 2002.



3. Split core samples were taken two months after the manipulation and the following year so that we could quantify individuals and species inhabiting zebra mussel colonies separately from those in sediments underlying zebra mussel colonies and adjacent sediments lacking zebra mussels.



4. Zebra mussel-covered sediments supported more abundant and richer invertebrate communities than adjacent sediments lacking zebra mussels.



5. Abundance and richness patterns in zebra mussel-addition and removal treatments closely paralleled those in natural communities.



6. Despite severe oxygen depletion at the interface of underlying sediments and overlying zebra mussel colonies, most infaunal invertebrates responded positively to zebra mussel colonisation either by remaining in sediments underlying zebra mussel colonies or by migrating into zebra mussel colonies.

http://faculty.sacredheart.edu/beekeym/Beekey%20files/Beekey_zebcomm%20copy.pdf

Zebra mussel colonisation of soft sediments facilitates invertebrate communities

The introduction of zebra mussels (Dreissena spp.) to North America has resulted in dramatic changes to the complexity of benthic habitats. Changes in habitat complexity may have profound effects on predator-prey interactions in aquatic communities. Increased habitat complexity may affect prey and predator dynamics by reducing encounter rates and foraging success. Zebra mussels form thick contiguous colonies on both hard and soft substrates. While the colonization of substrata by zebra mussels has generally resulted in an increase in both the abundance and diversity of benthic invertebrate communities, it is not well known how these changes affect the foraging efficiencies of predators that prey on benthic invertebrates. We examined the effect of zebra mussels on the foraging success of four benthic predators with diverse prey-detection modalities that commonly forage in soft substrates: slimy sculpin (Cottus cognatus), brown bullhead (Ameirus nebulosus), log perch (Percina caprodes), and crayfish (Orconectes propinquus). We conducted laboratory experiments to assess the impact of zebra mussels on the foraging success of predators using a variety of prey species. We also examined habitat use by each predator over different time periods. Zebra mussel colonization of soft sediments significantly reduced the foraging efficiencies of all predators. However, the effect was dependent upon prey type. All four predators spent more time in zebra mussel habitat than in either gravel or bare sand. The overall effect of zebra mussels on benthic-feeding fishes is likely to involve a trade-off between the advantages of increased density of some prey types balanced against the reduction in foraging success resulting from potential refugia offered in the complex habitat created by zebra mussels.

http://faculty.sacredheart.edu/beekeym/Beekey%20files/Beekey_zebforaging%20copy.pdf

Declan J. McCabe

Papers

Species co-occurrence: a meta-analysis of j. m. diamond's assembly rules model

Effects of disturbance frequency, intensity, and area on assemblages of stream macroinvertebrates

Factors affecting the movement of adult zebra mussels (Dreissena polymorpha)

Zebra mussel colonisation of soft sediments facilitates invertebrate communities

Zebra mussels affect benthic predator foraging success and habitat choice on soft sediments