Thomas J. Webb

On the Heritability of Geographic Range Sizes

Within taxonomic groups, most species are restricted in their geographic range sizes, with only a few being widespread. The possibility that species‐level selection on range sizes contributes to the characteristic form of such species–range size distributions has previously been raised. This would require that closely related species have similar range sizes, an indication of “heritability” of range sizes at the species level. Support for this view came from a positive correlation between the range sizes of closely related pairs of fossil mollusc species. We extend this analysis by considering the relationship between the geographic range sizes of 103 pairs of contemporary avian sister species. Range sizes in these sister species show no evidence of being more similar to each other than expected by chance. A reassessment of the mollusc data also suggests that the high correlation was probably overestimated because of the skewed nature of range size data. The fact that sister species tend to have similar life histories and ecologies suggests that any relationship between range sizes and biology is likely to be complicated and will be influenced by historical factors, such as mode of speciation and postspeciation range size transformations.

Biodiversity's Big Wet Secret: The Global Distribution of Marine Biological Records Reveals Chronic Under-Exploration of the Deep Pelagic Ocean

Background Understanding the distribution of marine biodiversity is a crucial first step towards the effective and sustainable management of marine ecosystems. Recent efforts to collate location records from marine surveys enable us to assemble a global picture of recorded marine biodiversity. They also effectively highlight gaps in our knowledge of particular marine regions. In particular, the deep pelagic ocean – the largest biome on Earth – is chronically under-represented in global databases of marine biodiversity. Methodology/Principal Findings We use data from the Ocean Biogeographic Information System to plot the position in the water column of ca 7 million records of marine species occurrences. Records from relatively shallow waters dominate this global picture of recorded marine biodiversity. In addition, standardising the number of records from regions of the ocean differing in depth reveals that regardless of ocean depth, most records come either from surface waters or the sea bed. Midwater biodiversity is drastically under-represented. Conclusions/Significance The deep pelagic ocean is the largest habitat by volume on Earth, yet it remains biodiversitys big wet secret, as it is hugely under-represented in global databases of marine biological records. Given both its value in the provision of a range of ecosystem services, and its vulnerability to threats including overfishing and climate change, there is a pressing need to increase our knowledge of Earths largest ecosystem.

Only half right: species with female-biased sexual size dimorphism consistently break Rensch's rule.

Background Most animal species display Sexual Size Dimorphism (SSD): males and females consistently attain different sizes, most frequently with females being larger than males. However the selective mechanisms driving patterns of SSD remain controversial. ‘Renschs rule’ proposes a general scaling phenomenon for all taxa, whereby SSD increases with average body size when males are larger than females, and decreases with body size when females are larger than males. Renschs rule appears to be general in the former case, but there is little evidence for the rule when females are larger then males. Methodology/Principal Findings Using comprehensive data for 1291 species of birds across 30 families, we find strong support for Renschs rule in families where males are typically larger than females, but no overall support for the rule in families with female-biased SSD. Reviewing previous studies of a broad range of taxa (arthropods, reptiles, fish and birds) showing predominantly female-biased SSD, we conclude that Renschs conjecture is the exception rather than the rule in such species. Conclusions/Significance The absence of consistent scaling of SSD in taxa with female-biased SSD, the most prevalent direction of dimorphism, calls into question previous general evolutionary explanations for Renschs rule. We propose that, unlike several other ecological scaling relationships, Renschs rule does not exist as an independent scaling phenomenon.

Distributions of Habitat Suitability and the Abundance‐Occupancy Relationship

Positive abundance‐occupancy relationships (a relationship between the number of sites a species occupies and the average density of individuals in occupied sites) are widespread through a range of taxa. The simplest model for this is the “vital rates” model, which proposes that habitat suitability varies spatially; increasing average habitat quality thus leads to simultaneous increases in average densities within occupied areas, as well as the total area that is habitable. This model has not been tested. We develop a general analytical version of this model and show that it predicts that the skewness of population size or aggregation of individuals within sites should vary systematically with density and occupancy, depending on the distribution of habitat suitability, and that the variance in occupancy should be highest at low densities. We compare these predictions with data from the British Trust for Ornithology’s Common Birds Census, and we find systematic changes in both variance and skewness of density, both intra‐ and interspecifically.

Does double-blind review benefit female authors?

Peer review is widely held to be essential for enhancing the quality of scientific communications [1]. Opinions differ, however, as to how to ensure that reviews are as fair and objective as possible. Most ecology and evolution journals employ a single-blind system, which conceals reviewer, but not author, identity. An alternative is double-blind review (both author and reviewer identity is concealed), which, surveys of authors and reviewers suggested, is popular [1] despite the fact that many of those surveyed actually had not experienced the system and that reviewers often like to know the identity of an author so that new work can be placed in context [1,2].

Fewer invited talks by women in evolutionary biology symposia

Lower visibility of female scientists, compared to male scientists, is a potential reason for the under‐representation of women among senior academic ranks. Visibility in the scientific community stems partly from presenting research as an invited speaker at organized meetings. We analysed the sex ratio of presenters at the European Society for Evolutionary Biology (ESEB) Congress 2011, where all abstract submissions were accepted for presentation. Women were under‐represented among invited speakers at symposia (15% women) compared to all presenters (46%), regular oral presenters (41%) and plenary speakers (25%). At the ESEB congresses in 2001–2011, 9–23% of invited speakers were women. This under‐representation of women is partly attributable to a larger proportion of women, than men, declining invitations: in 2011, 50% of women declined an invitation to speak compared to 26% of men. We expect invited speakers to be scientists from top ranked institutions or authors of recent papers in high‐impact journals. Considering all invited speakers (including declined invitations), 23% were women. This was lower than the baseline sex ratios of early‐mid career stage scientists, but was similar to senior scientists and authors that have published in high‐impact journals. High‐quality science by women therefore has low exposure at international meetings, which will constrain Evolutionary Biology from reaching its full potential. We wish to highlight the wider implications of turning down invitations to speak, and encourage conference organizers to implement steps to increase acceptance rates of invited talks.

FOREST COVER–RAINFALL RELATIONSHIPS IN A BIODIVERSITY HOTSPOT: THE ATLANTIC FOREST OF BRAZIL

It is now generally accepted that the relationship between vegetation and climate is dynamic: vegetation is influenced by climate, but feedbacks between terrestrial ecosystems and the atmosphere mean that vegetation also affects climate. From this it follows that land-use changes may have climatic consequences. Specifically, it is widely believed that forest clearance may inhibit rainfall. Although models often support this view, this is not universally the case, and empirical evidence is scarce. We have compiled a database of forest cover and precipitation for the state of Sao Paulo, which lies within the diverse and highly endangered Atlantic forest region of Brazil. We do not find a strong relationship between forest cover and total rainfall, which appears to be influenced primarily by factors such as distance to the coast; but significant positive relationships between tree cover and the number of rain days consistently emerge. The degree of forest fragmentation seems to influence this relationship, w...

What is macroecology

The symposium ‘What is Macroecology?’ was held in London on 20 June 2012. The event was the inaugural meeting of the Macroecology Special Interest Group of the British Ecological Society and was attended by nearly 100 scientists from 11 countries. The meeting reviewed the recent development of the macroecological agenda. The key themes that emerged were a shift towards more explicit modelling of ecological processes, a growing synthesis across systems and scales, and new opportunities to apply macroecological concepts in other research fields.

Heritability of Geographic Range Sizes Revisited: A Reply to Hunt et al.

Hunt et al.(2005) revisit the issue of range size heritability following our recent article on this topic (Webb and Gaston 2003). In that article, we showed that the range sizes of closely related species tend to be highly dissimilar and argued that this provided evidence to counter Jablonski’s (1987) claim that range size was a heritable species-level trait. Hunt et al. do not dispute the fact that the species pairs that we examined have highly asymmetric range sizes; however, they claim that the statistical technique that we used to assess the significance of this asymmetry is flawed. They then return to correlation analyses to support their assertion that range size is indeed heritable. While some points of technical interest are raised, we disagree with their conclusions and feel that the analyses that they present provide little insight into the ultimate questions.

Global patterns of extinction risk in marine and non-marine systems.

Despite increasing concern over the effects of human activities on marine ecosystems, extinction in the sea remains scarce: 19-24 out of a total of >850 recorded extinctions implies a 9-fold lower marine extinction rate compared to non-marine systems. The extent of threats faced by marine systems, and their resilience to them, receive considerable attention, but the detectability of marine extinctions is less well understood. Before its extinction or threat status is recorded, a species must be both taxonomically described and then formally assessed; lower rates of either process for marine species could thus impact patterns of extinction risk, especially as species missing from taxonomic inventories may often be more vulnerable than described species. We combine data on taxonomic description with conservation assessments from the International Union for Conservation of Nature (IUCN) to test these possibilities across almost all marine and non-marine eukaryotes. We find that the 9-fold lower rate of recorded extinctions and 4-fold lower rate of ongoing extinction risk across marine species can be explained in part by differences in the proportion of species assessed by the IUCN (3% cf. 4% of non-marine species). Furthermore, once taxonomic knowledge and conservation assessments pass a threshold level, differences in extinction risk between marine and non-marine groups largely disappear. Indeed, across the best-studied taxonomic groups, there is no difference between marine and non-marine systems, with on average between 20% and 25% of species being threatened with extinction, regardless of realm.