Revealing uncertainty in the status of biodiversity change

Biodiversity faces unprecedented threats from rapid global change1. Signals of biodiversity change come from time-series abundance datasets for thousands of species over large geographic and temporal scales. Analyses of these biodiversity datasets have pointed to varied trends in abundance, including increases and decreases. However, these analyses have not fully accounted for spatial, temporal and phylogenetic structures in the data. Here, using a new statistical framework, we show across ten high-profile biodiversity datasets2-11 that increases and decreases under existing approaches vanish once spatial, temporal and phylogenetic structures are accounted for. This is a consequence of existing approaches severely underestimating trend uncertainty and sometimes misestimating the trend direction. Under our revised average abundance trends that appropriately recognize uncertainty, we failed to observe a single increasing or decreasing trend at 95% credible intervals in our ten datasets. This emphasizes how little is known about biodiversity change across vast spatial and taxonomic scales. Despite this uncertainty at vast scales, we reveal improved local-scale prediction accuracy by accounting for spatial, temporal and phylogenetic structures. Improved prediction offers hope of estimating biodiversity change at policy-relevant scales, guiding adaptive conservation responses.

Survival rates of tropical and temperate passerines: a Trinidadian perspective

Mark-recapture data collected using mist nets over a 10-yr period in Trinidad were used to estimate adult survival rates for 17 species of forest passerines. Trinidadian survival rates (mean 65%, range 45%-85%) were significantly higher than published estimates for European (mean survival 52%, range 32%-71%) and North American (mean survival 53%, range 29%-63%) passerines of similar body size (equivalent to 45% higher mean life expectancy in Trinidad). These findings were confirmed after controlling for phylogeny using a method of independent contrasts. Transient and/or young birds were an important feature of the Trinidad data, and studies that fail to allow for the presence of such birds risk underestimating adult survival. This study lends support to the hypothesis that avian survival rates are higher in the humid tropics, although the magnitude of the difference may be smaller than previously suggested.

Using presence-absence data to establish reserve selection procedures that are robust to temporal species turnover

Previous studies suggest that a network of nature reserves with maximum efficiency (obtained by selecting the minimum area such that each species is represented once) is likely to be insufficient to maintain species in the network over time. Here, we test the performance of three selection strategies which require presence-absence data, two of them previously proposed (multiple representations and selecting an increasing percentage of each species' range) and a novel one based on selecting the site where each species has exhibited a higher permanence rate in the past. Multiple representations appear to be a safer strategy than selecting a percentage of range because the former gives priority to rarer species while the latter favours the most widespread. The most effective strategy was the one based on the permanence rate, indicating that the robustness of reserve networks can be improved by adopting reserve selection procedures that integrate information about the relative value of sites. This strategy was also very efficient, suggesting that the investment made in the monitoring schemes may be compensated for by a lower cost in reserve acquisition.

Association of osteopontin with calcification in human mitral valves

BACKGROUND

Little is known about the long-standing inflammation leading to calcification within heart valves. Osteopontin, a phosphorylated glycoprotein, is present within atheromatous calcific plagues in response to vascular endothelial injury. The purpose of the study was to investigate whether osteopontin exists in calcific mitral valve leaflets in human beings, and to determine a link between chronic inflammation leading to mitral stenosis and the osteopontin status of mitral valvular tissue.

MATERIALS AND METHODS

We reviewed the case histories of 17 patients who underwent mitral valve replacement therapy for mitral stenosis between 1995 and 1997 (8 men and 9 women, mean age 61 years). Hybrid mouse monoclonal immunoglobulin G1 antibodies were used for immunohistochemical detection of osteopontin in the acetone-fixed specimen. The control group consisted of normal mitral valve tissue from cardiomyopathy patients who underwent cardiac transplantation.

RESULTS

A weak osteopontin immunoreactivity was present in apparently normal mitral valve tissue obtained from cardiomyopathy patients. All mitral stenosis patients had immunoreactivity (17/17) for osteopontin within calcific deposits of mitral valve tissue. The intensity of osteopontin activity had a strong association with increasing macrophage and calcium aggregations in the mitral valvular tissue. We found no correlation between osteopontin status and clinical features on the prognosis of calcific mitral stenosis.

CONCLUSIONS

We conclude that osteopontin coexists with intimal macrophages in calcific human mitral valve tissue. Demonstration of such association between the presence of osteopontin and calcification in human mitral valves is consistent with the hypothesis that calcification in this tissue is, at least in part, an actively mediated phenomenon.

Robustness of reserve selection procedures under temporal species turnover

Complementarity-based algorithms for the selection of reserve networks emphasize the need to represent biodiversity features efficiently, but this may not be sufficient to maintain those features in the long term. Here, we use data from the Common Birds Census in Britain as an exemplar data set to determine guidelines for the selection of reserve networks which are more robust to temporal turnover in features. The extinction patterns found over the 1981-1991 interval suggest that two such guidelines are to represent species in the best sites where they occur (higher local abundance) and to give priority to the rarer species. We tested five reserve selection strategies, one which finds the minimum representation set and others which incorporate the first or both guidelines proposed. Strategies were tested in terms of their efficiency (inversely related to the total area selected) and effectiveness (inversely related to the percentage of species lost) using data on eight pairs of ten-year intervals. The minimum set strategy was always the most efficient, but suffered higher species loss than the others, suggesting that there is a trade-off between efficiency and effectiveness. A desirable compromise can be achieved by embedding the concerns about the long-term maintenance of the biodiversity features of interest in the complementarity-based algorithms.

Of mice and wrens: the relation between abundance and geographic range size in British mammals and birds

We examine the relation between population size and geographic range size for British breeding birds and mammals. As for most other assemblages studied, a strong positive interspecific correlation is found in both taxa. The relation is also recovered once the phylogenetic relatedness of species has been controlled for using an evolutionary comparative method. The slope of the relation is steeper for birds than for mammals, but this is due in large part to two species of mammals that have much higher population sizes than expected from their small geographic ranges. These outlying mammal species are the only ones in Britain to be found only on small offshore islands, and so may be exhibiting density compensation effects. With them excluded, the slope of the abundance–range size relation for mammals is not significantly different to that for birds. However, the elevation of the relation is higher for mammals than for birds, indicating that mammals are approximately 30 times more abundant than birds of equivalent geographic range size. An earlier study of these assemblages showed that, for a given body mass, bats had abundances more similar to birds than to non–volant mammals, suggesting that the difference in abundance between mammals and birds might be due to constraints of flight. Our analyses show that the abundance–range size relation for bats is not different for that from other mammals, and that the anomalously low abundance of bats for their body mass may result because they have smaller than expected geographic extents for their size. Other reasons why birds and mammals might have different elevations for the relation between population size and geographic range size are discussed, together with possible reasons for why the slopes of these relations might be similar.

Sampling Effort and Parasite Species Richness

Comparative studies of parasite species richness among host taxa can be confounded by uneven sampling effort. Sampling ceases to be a confounding factor when extrapolation methods are used to estimate true species richness. Here, Bruno Walther and colleagues review examples of sampling bias and the use of extrapolation methods for circumventing it. They also discuss the confounding effects of phylogenetic association of estimates of species richness.

Quantification of parasite aggregation: a simulation study

A simulation study is used to examine the statistical behaviour of estimators of parameters of parasite infection in relation to variation in sample size, the degree of parasite aggregation, and mean parasite burden. The most important patterns to emerge are the associations between estimates of parameters and sample size (= number of host individuals). As sample size decreases values of sample mean parasite burden, its associated variance, and the level of parasite aggregation are all systematically underestimated. The geometric mean of parasite burden and the prevalence of infection appear to be independent of associations with other parasite parameters. Estimates of parameter values may also depend on the underlying frequency distribution, but appear insensitive to variation in the population mean parasite burden. Results are discussed in relation to the interpretation of data derived from field-based studies. In particular, establishing the form of the relationship between host age and mean parasite burden and/or the degree of parasite aggregation. It is typical for sample size to decline as a function of host age within cross-sectional field data. This may give rise to artefactual patterns in the shape of age-aggregation curves in which sample sizes are unequal among host age classes.

Parasite prevalence and host sample size

Parasite prevalence is a summary statistic familiar to biologists. However, that there is an interspecific relationship between prevalence and sample size (the number of host individuals examined for parasites) is not widely appreciated. In this article, Richard Gregory and Tim Blackburn present some examples of this negative relationship, explain the mechanisms that underlie this pattern and discuss the potential problems this association might create for biological studies.