Taxonomic and geographic bias in 50 years of research on the behaviour and ecology of galagids

Identifying knowledge gaps and taxonomic and geographic bias in the literature is invaluable for guiding research towards a more representative understanding of animal groups. Galagids are nocturnal African primates and, for many species, detailed information on their behaviour and ecology is unavailable. To identify gaps and bias in the literature we reviewed published peer-reviewed research articles on galagid behaviour and ecology over a 50-year period from January 1971 to December 2020. Using the Web of Science and Google Scholar databases, we identified 758 articles, assessed 339 full texts for eligibility and included 211 in the review. Species of Otolemur have been extensively researched in comparison to other genera (78.2% of studies; Euoticus: 13.3% of studies; Galago: 66.4% of studies; Galagoides: 20.9% of studies; Paragalago: 22.3% of studies; Sciurocheirus: 15.2% of studies). The most common category of research was physiology (55.0% of studies), followed by behavioural ecology (47.4% of studies), and fewer studies were on genetics and taxonomy (16.1% of studies) and habitat and distribution (14.2% of studies). Text mining revealed that the word ‘behaviour’ was the most common word used in abstracts and keywords, and few words were related to ecology. Negative binomial regression revealed that mean body mass and geographic range size were significant positive predictors of the total number of scientific outputs on each species. Research on wild populations was carried out in only 24 (60%) of the 40 countries galagids are thought to inhabit. Studies were undertaken in locations with lower mean annual temperatures and higher human population densities over warmer and less populated areas. We encourage a more equal sampling effort both taxonomically and geographically that in particular addresses the paucity of research on smaller species and those with restricted ranges. Research on in situ populations, especially in warmer and remote areas, is urgently needed, particularly in West, Central and some Southern African countries.

Fungi in soil and understory have coupled distribution patterns

Ecological processes that control fungal distribution are not well understood because many fungi can persist in a wide variety of dissimilar habitats which are seldom sampled simultaneously. Geographic range size is reflective of species’ resource usage, and for plants and animals, there is a robust positive correlation between niche-breadth and range-size. It remains unknown whether this pattern is true for fungi. To investigate the fungal niche breadth–range size relationship we identified habitat specialists and generalists from two habitats (plant leaves and soil) and asked whether habitat specialization influenced fungal biogeography. We sampled fungi from the soil and phylloplane of tropical forests in Vanuatu and used DNA metabarcoding of the fungal ITS1 region to examine rarity, range size, and habitat connectivity. Fungal communities from the soil and phylloplane are spatially autocorrelated and the spatial distribution of individual fungal OTU are coupled between habitats. Habitat breadth (generalist fungi) did not result in larger range sizes but did correlate positively with occurrence frequency. Fungi that were frequently found were also found in high abundance, a common observation in similar studies of plants and animals. Fungal abundance-occupancy relationships differed by habitat and habitat-specificity. Soil specialists were found to be locally abundant but restricted geographically. In contrast, phylloplane generalists were found to be abundant over a large range in multiple habitats. These results are discussed in the context of differences between habitat characteristics, stability and spatial distribution. Identifying factors that drive spatial variation is key to understanding the mechanisms that maintain biodiversity in forests.

A latitudinal signal in the relationship between species geographic range size and climatic niche area

Species with broader niches may have the opportunity to occupy larger geographic areas, assuming no limitations on dispersal and a relatively homogeneous environmental space. While there is general support for positive \textit{geographic range size – climatic niche area} relationships, a great deal of variation exists across taxonomic and spatial gradients. Here, we use data on a large set of mammal ($n$ = 1225), bird ($n$ = 1829), and tree ($n$ = 341) species distributed across the Americas to examine the \textbf{1}) relationship between geographic range size and climatic niche area, \textbf{2}) influence of species traits on species departures from the best fit geographic range size – climatic niche area relationship, and \textbf{3}) how detection of these relationships is sensitive to how species range size and climatic niche area are estimated. We find positive \textit{geographic range size – climatic niche area} relationships for all taxa. Residual variation in this relationship contained a strong latitudinal signal. Subsampling the occurrence data to create a null expectation, we found that residual variation did not strongly deviate from the null expectation. Together, we provide support for the generality of \textit{geographic range size – climatic niche area} relationships, which may be constrained by latitude but are agnostic to species identity, suggesting that species traits are far less responsible than geographic barriers and the distribution of land area and available environmental space.

Dimensions of invasiveness: Links between local abundance, geographic range size, and habitat breadth in Europe’s alien and native floras

Understanding drivers of success for alien species can inform on potential future invasions. Recent conceptual advances highlight that species may achieve invasiveness via performance along at least three distinct dimensions: 1) local abundance, 2) geographic range size, and 3) habitat breadth in naturalized distributions. Associations among these dimensions and the factors that determine success in each have yet to be assessed at large geographic scales. Here, we combine data from over one million vegetation plots covering the extent of Europe and its habitat diversity with databases on species’ distributions, traits, and historical origins to provide a comprehensive assessment of invasiveness dimensions for the European alien seed plant flora. Invasiveness dimensions are linked in alien distributions, leading to a continuum from overall poor invaders to super invaders—abundant, widespread aliens that invade diverse habitats. This pattern echoes relationships among analogous dimensions measured for native European species. Success along invasiveness dimensions was associated with details of alien species’ introduction histories: earlier introduction dates were positively associated with all three dimensions, and consistent with theory-based expectations, species originating from other continents, particularly acquisitive growth strategists, were among the most successful invaders in Europe. Despite general correlations among invasiveness dimensions, we identified habitats and traits associated with atypical patterns of success in only one or two dimensions—for example, the role of disturbed habitats in facilitating widespread specialists. We conclude that considering invasiveness within a multidimensional framework can provide insights into invasion processes while also informing general understanding of the dynamics of species distributions.

Pollinator habitat plantings benefit wild, native bees, but do not necessarily favor rare species

Installing pollinator habitat is a ubiquitous conservation tool, but little is known about which pollinator taxa require support, or which benefit from habitat installations. We studied the response of rare and common bees to pollinator habitat enhancement. We used independent regional datasets to designate bee species as common or rare based on their rank according to one of three metrics: a) site occurrence frequency, b) local relative abundance, and c) geographic range size. We asked whether the abundance or richness of rare and common bees were greater in pollinator habitat, relative to old-field controls. Because we used an arbitrary, quantile-based cutoff to categorize species rarity, we conducted sensitivity analysis and controlled for rarity classification errors with a null model. With this null model, we determined whether rare and/or common species responded to pollinator habitat disproportionately, compared to the expectation for "typical" bee species. We found that the number of individuals and of species designated as rare based on local relative abundance was greater in pollinator habitat enhancements. The number of individuals from bee species designated as rare based on site occurrence was lower in pollinator habitat enhancements, but the number of species was not clearly different between habitat types. We did not find a clear positive nor negative effect of habitat enhancement for species designated rare based on geographic range size. For all three rarity metrics, common species increased in abundance and richness in pollinator habitat relative to controls. Null models indicated that in most cases, neither rare nor common species disproportionately benefited from pollinator habitat. Synthesis and Applications: Our results suggest that pollinator habitat can lead to an increase in the abundance and richness of bees, including species that are rare and that are common. However, rare species appeared to respond differently than typical species, and depending on how species were classified as rare, could display muted or even negative responses to habitat enhancement. Targeting rare species with specific floral resources or unique habitat types may lead to better outcomes for rare and threatened species.

Relation between the habitat niche breadth and the geographic range size: A case study on palearctic voles (Mammalia: Rodentia: Arvicolinae)

Habitat niche breadth for Palearctic Arvicolinae species was estimated at both local (α- niche) and global (the entire geographic range, γ-niche) scales using occurrence records of species and environmental (climate, topography, and vegetation) data. Niche breadth was estimated in the space of the first two principal components of environmental variables using kernel smoothing of the densities of species occurrence points. The breadth of α-niches was estimated for a set of random points inside the geographic range in a series of buffers of increasing size around these points. Within each buffer, we calculated the overlap between the distribution of environment values for the kernel smoothed densities of species occurrence points and the distribution of environment values in the background environment. The α-niche breadth was calculated as the slope of the linear regression of the niche breadth for buffers of different size by the ln area of these buffers with a zero intercept. The γ-niche breadth was calculated as the overlap between the distributions of environmental values for the kernel smoothed densities of species occurrence points over the whole geographic range and the distribution of environmental values in the background environment and also approximated by linear regression of the species’ average α-niche to the geographic range area of this species. The results demonstrated that the geographic range size was significantly related with the α- and γ-niche breadth. The γ-niche breadth was significantly positively correlated with the α-niche breadth. Finally, the differences between the γ-niche breadth values that were directly estimated and extrapolated from the α-niche breadth (Δ) values were positively correlated with the geographic range size. Thus, we conclude that the species occupy larger geographic ranges because they have broader niches. Our estimations of the γ-niche breadth increase with the geographic range size not due to a parallel increase of the environmental diversity (spatial autocorrelation in the environment).

Comparing Genetic Diversity in Three Threatened Oaks

Genetic diversity is a critical resource for species’ survival during times of environmental change. Conserving and sustainably managing genetic diversity requires understanding the distribution and amount of genetic diversity (in situ and ex situ) across multiple species. This paper focuses on three emblematic and IUCN Red List threatened oaks (Quercus, Fagaceae), a highly speciose tree genus that contains numerous rare species and poses challenges for ex situ conservation. We compare the genetic diversity of three rare oak species—Quercus georgiana, Q. oglethorpensis, and Q. boyntonii—to common oaks; investigate the correlation of range size, population size, and the abiotic environment with genetic diversity within and among populations in situ; and test how well genetic diversity preserved in botanic gardens correlates with geographic range size. Our main findings are: (1) these three rare species generally have lower genetic diversity than more abundant oaks; (2) in some cases, small population size and geographic range correlate with genetic diversity and differentiation; and (3) genetic diversity currently protected in botanic gardens is inadequately predicted by geographic range size and number of samples preserved, suggesting non-random sampling of populations for conservation collections. Our results highlight that most populations of these three rare oaks have managed to avoid severe genetic erosion, but their small size will likely necessitate genetic management going forward.

Geographic contingency, not species sorting, dominates macroevolutionary dynamics in an extinct clade of neogastropods (Volutospina; Volutidae)

Rates of speciation and extinction are often linked to many ecological factors, traits (emergent and nonemergent) such as environmental tolerance, body size, feeding type, and geographic range. Marine gastropods in particular have been used to examine the role of larval dispersal in speciation. However, relatively few studies have been conducted placing larval modes in species-level phylogenetic context. Those that have, have not incorporated fossil data, while landmark macroevolutionary studies on fossil clades have not considered both phylogenetic context and net speciation (speciation–extinction) rates. This study utilizes Eocene volutid Volutospina species from the U.S. Gulf Coastal Plain and the Hampshire Basin, U.K., to explore the relationships among larval mode, geographic range, and duration. Based on the phylogeny of these Volutospina, we calculated speciation and extinction rates in order to compare the macroevolutionary effects of larval mode. Species with planktotrophic larvae had a median duration of 9.7 Myr, which compared significantly to 4.7 Myr for those with non-planktotrophic larvae. Larval mode did not significantly factor into geographic-range size, but U.S. and U.K. species do differ, indicating a locality-specific component to maximum geographic-range size. Non-planktotrophs (NPTs)were absent among the Volutospina species during the Paleocene–early Eocene. The relative proportions of NPTs increased in the early middle Eocene, and the late Eocene was characterized by disappearance of planktotrophs (PTs). The pattern of observed lineage diversity shows an increasing preponderance of NPTs; however, this is clearly driven by a dramatic extinction of PTs, rather than higher NPT speciation rates during the late Eocene. This study adds nuance to paleontology's understanding of the macroevolutionary consequences of larval mode.

Consistent replacement of small- by large-ranged plant species across habitats

The direction and magnitude of long-term changes in local plant species richness are highly variable among studies, while species turnover is ubiquitous. However, it is unknown whether the nature of species turnover is idiosyncratic or whether certain types of species are consistently gained or lost across different habitats. To address this question, we analyzed the trajectories of 1,827 vascular plant species over time intervals of up to 78 years at 141 sites in three habitats in Europe – mountain summits, forests, and lowland grasslands. Consistent across all habitats, we found that plant species with small geographic ranges tended to be replaced by species with large ranges, despite habitat-specific trends in species richness. Our results point to a predictable component of species turnover, likely explained by aspects of species’ niches correlated with geographic range size. Species with larger ranges tend to be associated with nutrient-rich sites and we found community composition shifts towards more nutrient-demanding species in all three habitats. Global changes involving increased resource availability are thus likely to favor large-ranged, nutrient-demanding species, which are typically strong competitors. Declines of small-ranged species could reflect not only abiotic drivers of global change, but also biotic pressure from increased competition. Our study highlights the need to consider the traits of species such as the geographic range size when predicting how ecological communities will respond to global change.