Summary1. Policy-makers increasingly demand robust measures of biodiversity change over short time periods. Longterm monitoring schemes provide high-quality data, often on an annual basis, but are taxonomically and geographically restricted. By contrast, opportunistic biological records are relatively unstructured but vast in quantity. Recently, these data have been applied to increasingly elaborate science and policy questions, using a range of methods. At present, we lack a firm understanding of which methods, if any, are capable of delivering unbiased trend estimates on policy-relevant time-scales. 2. We identified a set of candidate methods that employ data filtering criteria and/or correction factors to deal with variation in recorder activity. We designed a computer simulation to compare the statistical properties of these methods under a suite of realistic data collection scenarios. We measured the Type I error rates of each method-scenario combination, as well as the power to detect genuine trends. 3. We found that simple methods produce biased trend estimates, and/or had low power. Most methods are robust to variation in sampling effort, but biases in spatial coverage, sampling effort per visit, and detectability, as well as turnover in community composition, all induced some methods to fail. No method was wholly unaffected by all forms of variation in recorder activity, although some performed well enough to be useful. 4. We warn against the use of simple methods. Sophisticated methods that model the data collection process offer the greatest potential to estimate timely trends, notably Frescalo and occupancy-detection models. 5. The potential of these methods and the value of opportunistic data would be further enhanced by assessing the validity of model assumptions and by capturing small amounts of information about sampling intensity at the point of data collection.

A massive enlargement of the gill surface proved to be an important factor in the hypoxia survival of young cichlids. Because the heads of cichlids are densely packed with structures related to both feeding and breathing, we hypothesized that the extra space needed for gill enlargement requires such large structural reorganizations that outer head shape is affected. We used a three-dimensional model to describe changes in the outer head shape of cichlids. Broods of cichlids of different phylogenetic lineages, habitats, and trophic specialization were split and raised at either 10% or 80-90% air saturation. Despite the above-mentioned differences between the species that were used, all hypoxia raised groups showed similar volume enlargements. Volume increases were most prominent in the ventral suspensorial and ventral opercular subcompartments. A relation with the enlarged gills of hypoxia raised fish is likely because the gills are mainly located in these compartments. The differences in ventral width correspond to those found in other studies comprising a wide variety of genotypic and phenotypic variations. The present study shows that such variation in the ventral width is conceivable by phenotypic plasticity alone.

1. Policy-makers increasingly demand robust measures of biodiversity change over short time periods. Long-term monitoring schemes provide high-quality data, often on an annual basis, but are taxonomically and geographically restricted. By contrast, opportunistic biological records are relatively unstructured but vast in quantity. Recently, these data have been applied to increasingly elaborate science and policy questions, using a range of methods. At present we lack a firm understanding of which methods, if any, are capable of delivering unbiased trend estimates on policy-relevant timescales. 2. We identified a set of candidate methods that employ either selection criteria or correction factors to deal with variation in recorder activity. We designed a computer simulation to compare the statistical properties of these methods under a suite of realistic data collection scenarios. We measured the Type I error rates of each method-scenario combination, as well as the power to detect genuine trends. 3. We found that simple methods produce biased trend estimates, and/or had low power. Most methods are robust to variation in sampling effort, but biases in spatial coverage, sampling effort per visit, and detectability, as well as turnover in community composition all induced some methods to fail. No method was robust to all forms of variation in recorder activity. 4. We warn against the use of simple methods. We identify three methods with complementary strengths and weaknesses that are useful for estimating timely trends. Sophisticated correction factor methods, including Occupancy and Frescalo, offer the greatest potential in the long-term. Methods based solely on selection criteria are inherently limited, but a combination or ensemble of approaches may be required to generate trends that are both robust and powerful. Small amounts of information about sampling intensity, captured at the point of data collection, would greatly enhance the utility of opportunistic data and make future trend estimates more reliable

Two new species of zooplanktivorous haplochromine cichlids from Lake Victoria, Tanzania, are described and illustrated. These species closely resemble each other. Their affinities to other zooplanktivorous haplochromines from Lake Victoria are discussed. Haplochromis argens sp. n., which featured under nicknames (mainly Haplochromis “argens”) in more than 50 papers, was caught both in the Mwanza Gulf and the Emin Pasha Gulf, whereas Haplochromis goldschmidti sp. n. was only found in the Emin Pasha Gulf. Of the latter species only males are available, but it seems unlikely that it represents a case of male colour polymorphism as several presumably unrelated characters differ in sympatry between the two species, suggesting that there is no gene flow. Statistical analysis revealed that the overall difference between the two species is greater than that between the populations from the two locations. Body depth of the two species in sympatry in the Emin Pasha Gulf was more similar than that of Haplochromis goldschmidti sp. n. and the allopatric population of Haplochromis argens sp. n. from the Mwanza Gulf,which mayindicate an overall environmental effect. However, several measurements related to the width of snout and mouth differed more between the populations of the two species in sympatry than between the allopatric populations. In contrast to a group of zooplanktivorous species that recovered successfully after environmental changes in the lake, Haplochromis argens sp. n. is among a group that became extremely rare and probably is in danger of extinction; the conservation status of Haplochromis goldschmidti sp. n. is currently unknown.