Rarity value and species extinction: the anthropogenic Allee effect

Standard economic theory predicts that exploitation alone is unlikely to result in species extinction because of the escalating costs of finding the last individuals of a declining species. We argue that the human predisposition to place exaggerated value on rarity fuels disproportionate exploitation of rare species, rendering them even rarer and thus more desirable, ultimately leading them into an extinction vortex. Here we present a simple mathematical model and various empirical examples to show how the value attributed to rarity in some human activities could precipitate the extinction of rare species—a concept that we term the anthropogenic Allee effect. The alarming finding that human perception of rarity can precipitate species extinction has serious implications for the conservation of species that are rare or that may become so, be they charismatic and emblematic or simply likely to become fashionable for certain activities.     

‘Inordinate Fondness’: A Threat to Beetles in South East Asia?

A recent report on trade in stag beetles and rhinoceros beetles in Japan highlights a number of issues of considerable importance for beetle conservation resulting from such trade over much of south east Asia. The popularity of these beetles has both positive and negative effects, and there is need for more effective control and monitoring of this trade to enhance positive values and reduce likely harm to species and habitats.     

A multidimensional characterization of rarity applied to the Aegean tenebrionid beetles (Coleoptera Tenebrionidae)

This paper attempts to use museum collection data to estimate measures of species rarity and then to relate these measures to extinction risk. For this purpose, 170 taxa (138 species and 32 subspecies) of tenebrionid beetles from 32 Aegean Islands (Greece) were considered. For each taxon, rarity was evaluated as geographic distribution (mean incidence on islands in the archipelago), potential habitat exploitation (total area of the islands occupied on the total area of the study system) and contactability (number of decades of taxon’s records on the total number of decades of assumed persistence from 1870 to 2000). All of these indices were correlated to each other. Whether expressed in terms of range size or habitat exploitation rarity was a major determinant of a species’ risk of extinction (evaluated as extinction decade). Thus, the designation of rarity provides a good basis for identifying species that are most in need of conservation at a particular scale.     

The spatial variability of rare and common species in a gall-inhabiting Lepidoptera community

Determining the spatial variability in abundance structure of rare species is necessary to assess the validity of the often clarmed properties of rare species, I e as being both vulnerable to extinction and good indicators of environmental change The spatial concordance of the Lepidoptera species that inhabit a fungus-induced gall on Acacia karroo was examined across South Africa A positive relationship was found between species distribution and abundance The common and moderately common species in the community were highly concordant, although the rare species were diffusive As such, the vulnerability of the rare species in this community is difficult to assess and they are unlikely to make useful indicators of environmental change Although preliminary results suggest that the community is temporally concordant, establishing the level of temporal, in addition to spaual, concordance of rarity is necessary to determine the mechanisms responsible for the abundance structure of rare species in communities     

Patterns and correlates of plant diversity differ between common and rare species in a neotropical dry forest

Determining which factors affect species richness is important for conservation theory and practice. However, richness of common and rare species may be affected by different factors. We use an extensive inventory of woody plants from a tropical dry forest landscape in Yucatan, Mexico to assess the unique effects of environmental variables, spatial dependence of sampling sites, forest stand age and the combined effect of all groups of variables on species richness of woody plants with different levels of rarity (common, intermediate, rare, very rare)—according to their abundance, habitat specificity and spatial distribution range in the landscape. Analyzing separately common species and those with different levels of rarity uncovered contrasting patterns and correlates of species richness that were not apparent when focusing on all woody plants. In particular, richness of common and intermediate species was influenced mainly by environmental factors, whereas richness of very rare species was affected mostly by the unique effect of spatial dependence of sampling sites, suggesting a main role of environmental filtering and dispersal limitation, respectively. However, common and very rare species also responded inversely to some landscape metrics, revealing contrasting environmental preferences of these groups of species. These contrasting results suggest different underlying mechanisms and the need for very different conservation strategies. Therefore, basic and applied research on tropical forest biodiversity should consider separately species with different levels of rarity, focusing on which factors control variation in each level, and paying special attention to very rare species, generally the most specious and vulnerable to local extinction.     

Frugivorous butterfly species in tropical forest fragments: correlates of vulnerability to extinction

Insects exhibit a variety of population-level responses to forest fragmentation, ranging from population increase to extinction. However, the biological attributes that underlie differences in extinction vulnerability among insects have been little-studied. Using the frugivorous butterfly community of tropical dry forest in Venezuela, we studied body size, population density and colonization ability as attributes that might underlie the range of responses of insects to forest fragmentation. The study was carried out in a set of forest fragments in the reservoir Lago Guri, formed by the damming of the Caroni River in eastern Venezuela. Results show that larger butterfly species were more vulnerable to extinction from habitat fragments than smaller ones. Rarer species were not more vulnerable to extinction, showing that rarity may not be an important correlate of vulnerability to extinction amongst insects. Contrary to expectation, faster-flying species were more and not less vulnerable to extinction from small habitat fragments. We speculate on the possible reasons for the observed patterns in extinction vulnerability using additional observations on behavioural patterns and larval host plant distributions of some of the butterfly species.     

Long-term differences in extinction risk among the seven forms of rarity

Rarity is widely used to predict the vulnerability of species to extinction. Species can be rare in markedly different ways, but the relative impacts of these different forms of rarity on extinction risk are poorly known and cannot be determined through observations of species that are not yet extinct. The fossil record provides a valuable archive with which we can directly determine which aspects of rarity lead to the greatest risk. Previous palaeontological analyses confirm that rarity is associated with extinction risk, but the relative contributions of different types of rarity to extinction risk remain unknown because their impacts have never been examined simultaneously. Here, we analyse a global database of fossil marine animals spanning the past 500 million years, examining differential extinction with respect to multiple rarity types within each geological stage. We observe systematic differences in extinction risk over time among marine genera classified according to their rarity. Geographic range played a primary role in determining extinction, and habitat breadth a secondary role, whereas local abundance had little effect. These results suggest that current reductions in geographic range size will lead to pronounced increases in long-term extinction risk even if local populations are relatively large at present.     

Using rarity to infer how dendritic network structure shapes biodiversity in riverine communities

Dispersal of organisms connects physical localities, but the strength of connection varies widely. Variability in the influence of dispersal can be predictable in sharply defined networks like river systems because some sections of the network are more isolated, leading to different balances of local (i.e. environmental filtering, species interactions) and regional (i.e. dispersal‐driven) processes in structuring communities. We examined the influence of spatial isolation on the relative contributions of α‐ and β‐diversity to regional (γ) diversity, and examined how that influence differed between common and rare species in stream macroinvertebrate communities. One explanation for rarity on a regional scale is that common species are habitat generalists while rare species are specialists. Therefore, common species should be influenced more by dispersal‐driven processes while rare species should be more influenced by local processes. We predicted that for rare taxa, β‐diversity should represent a higher fraction of γ‐diversity in isolated headwaters but that differences between rare and common taxa with regard to the contribution of β‐diversity to γ‐diversity should be less distinct in well‐connected mainstem habitats. To test these predictions, we used macroinvertebrate communities from 634 sites across 22 watersheds. Regardless of rarity, β‐ and γ‐diversity were higher in headwaters compared to mainstems. However, α‐diversity was similar regardless of isolation for rare assemblages. But contrary to our predictions, common assemblages of predators and herbivores did exhibit differences in α‐diversity between locations. Our predictions were strongly supported for two guilds of consumers, the detritivores and collectors, but less so for herbivores and predators. However, these results make sense considering differences in life histories between the groups. For detritivores and collectors, species turnover (β‐diversity) was higher in isolated regions in river networks, and rarity exacerbated this effect, resulting in higher regional diversity of rare species, supporting the general theory that rarity reflects habitat specialization.     

Parthenogenesis is self-destructive for scaled reptiles

Parthenogenesis is rare in nature. With 39 described true parthenogens, scaled reptiles (Squamata) are the only vertebrates that evolved this reproductive strategy. Parthenogenesis is ecologically advantageous in the short term, but the young age and rarity of parthenogenetic species indicate it is less advantageous in the long term. This suggests parthenogenesis is self-destructive: it arises often but is lost due to increased extinction rates, high rates of reversal or both. However, this role of parthenogenesis as a self-destructive trait remains unknown. We used a phylogeny of Squamata (5388 species), tree metrics, null simulations and macroevolutionary scenarios of trait diversification to address the factors that best explain the rarity of parthenogenetic species. We show that parthenogenesis can be considered as self-destructive, with high extinction rates mainly responsible for its rarity in nature. Since these parthenogenetic species occur, this trait should be ecologically relevant in the short term.     

人文世界里的锹甲

锹甲作为一类观赏昆虫在人文世界里受到长久的关注,文章对人文世界里的锹甲进行回顾：综述不同国家和地区中锹甲的多种称谓;从历史文化角度追溯锹甲学名的由来、锹甲与天牛科学名的关系、欧洲宗教中的锹甲、民间故事与风俗中的锹甲;从艺术欣赏角度介绍锹甲与绘画、锹甲与邮票、锹甲与装饰;着眼与现实生活,对锹甲的综合现状进行评述,并总结锹甲作为物种正面临的问题,呼吁人们在欣赏锹甲的同时,更要关注锹甲的物种多样性保护。     

How local extinction changes rarity: an example with Sonoran Desert fishes

That spatially rare species may be predisposed to extinction is a common tenet of ecology. However, the opposite side of the relationship – how extinction alters spatial rarity – remains little explored. We used an extensive biodiversity database to contrast patterns of spatial rarity of a biogeographic assemblage of native Sonoran fishes before and after an extensive, decades-long wave of extirpations. Focusing on 25 fish species native to the Lower Basin of the Colorado River, we analyzed two key aspects of spatial rarity: 1) species range sizes (expressed as kilometers of stream reach occupied) and 2) species' co-occurrence patterns. Native fish species that were spatially rare historically suffered disproportionate losses in occurrences. However, endemic species did not suffer increased losses relative to non-endemic (but still native) species of comparable rarity. Species' geographic range sizes were concordant through time, with spatially rare species remaining rare after extensive extirpations relative to species that were historically more widespread. In contrast, extirpations greatly disrupted patterns of species co-occurrence on both local and regional scales. Over 50% of the species pairs that historically co-occurred (in the same 5  km reach) no longer co-occur anywhere in the Lower Basin, and species pairs that infrequently co-occurred in historic times suffered greater proportional losses than did more widely co-occurring pairs. Such changes in the relationship between spatial rarity and species richness deserve attention because they inhibit conservation planning (decreasing the efficiency of reserve design) and reduce interaction diversity altering opportunities for long-term co-evolutionary change.     

Potential impacts on Japanese fauna of canestriniid mites (Acari: Astigmata) accidentally introduced with pet lucanid beetles from Southeast Asia

To develop a risk-assessment system for small organisms accidentally introduced with imported organisms, we investigated as a first case study parasitic canestriniid mites, which have been imported into Japan via pet lucanid beetles from Southeast Asia. We collected mites from pinned specimens of Japanese lucanids collected before 1999—when the Japanese government lifted a ban on the import of the beetles—and living mites from imported and native lucanid beetles collected after that. No foreign canestriniid was found on any of the native Japanese beetles. Because the mites collected from imported beetles were different from Japanese species, we conclude that the foreign mites have not yet established wild populations in Japan. However, because the Japanese mites migrate between hosts without host physical contact, introduced mites are assumed to be able to migrate from a foreign to Japanese host. In fact, possible contamination was observed in pet shops. We observed host switching in only one direction: Southeast Asian Canestrinia nr spectanda switched to Japanese Dorcus rectus, but Japanese Coleopterophagus berlesei never switched to Indonesian D. titanus. The foreign mites reproduced between 15°C and 25°C, suggesting that the mites could survive in mountainous sites in southern Japan and at low elevations in northern Japan. The ability of foreign parasitic canestriniids to infect and survive on Japanese hosts at temperatures characteristic of much of Japan leads us to conclude that these mites present a potential risk to Japanese endemic canestriniids as well as to native Japanese lucanids.     

Rarity and persistence

Rarity is a population characteristic that is usually associated with a high risk of extinction. We argue here, however, that chronically rare species (those with low population densities over many generations across their entire ranges) may have individual‐level traits that make populations more resistant to extinction. The major obstacle to persistence at low density is successful fertilisation (union between egg and sperm), and chronically rare species are more likely to survive when (1) fertilisation occurs inside or close to an adult, (2) mate choice involves long‐distance signals, (3) adults or their surrogate gamete dispersers are highly mobile, or (4) the two sexes are combined in a single individual. In contrast, external fertilisation and wind‐ or water‐driven passive dispersal of gametes, or sluggish or sedentary adult life habits in the absence of gamete vectors, appear to be incompatible with sustained rarity. We suggest that the documented increase in frequency of these traits among marine genera over geological time could explain observed secular decreases in rates of background extinction. Unanswered questions remain about how common chronic rarity actually is, which traits are consistently associated with chronic rarity, and how chronically rare species are distributed among taxa, and among the world's ecosystems and regions.     

Multiple measures are necessary to assess rarity in macro-molluscs: a case study from southeastern Australia

Our knowledge of suitable criteria to determine rarity in most marine invertebrates is lacking, thus hindering targeted impact studies, long-term monitoring programs, and associated conservation strategies. Standardized definitions of rarity are required to enable comparisons of different assemblages and taxa. Gaston (Rarity, Chapman and Hall, Melbourne, 1994) has recommended that rare species are defined as the lowest quartile of species in the assemblage. In this study, the 25% ‘cut-off’ was applied to intertidal macro-molluscs along the Illawarra Coast, Australia from 200 surveys of 13 reefs, using three measures of population structure; (1) local abundance (numerical rarity); (2) number of locations (spatial rarity) and; (3) percent of surveys (temporal rarity). Rare species were consequently defined as those species with no more than; (1) a local abundance of two individuals; (2) a regional occurrence at two reefs and/or; (3) a temporal occurrence in 2% of all surveys. These cut-off values increased when only intertidal specialists were analysed. Using a combination of all three measures, 62 species (42%) were classified as regionally rare, but only four of these were true intertidal specialists. Most species were rare by only one or two definitions of rarity; illustrating the importance of considering multiple measures of rarity and the need to design specifically targeted survey methods for future monitoring. Many species that are rare by all three definitions are likely to be temporary immigrants, as subtidal species were significantly more likely to be classified as rare. Clearly many factors can influence the rarity of marine invertebrates on intertidal reefs, and these must all be considered to set appropriate conservation priorities.     

Taxon size predicts rates of rarity in vascular plants

We surveyed rarity in the vascular plants of the continental U.S.A. and Canada and the vascular plants of Hawaii to test the hypothesis that rates of rarity are independent of taxonomic group size. We demonstrated that taxonomic groups of plants with few species consistently contained fewer than the expected numbers of rare species. This pattern was apparent at the levels of genus, family, order and class. We also found that the pattern remained when we examined rates of rarity by comparing sister taxa that share a common ancestor. This pattern may arise from either differential speciation and extinction patterns or taxonomic bias in species designations (lumping and splitting). The pattern of lineages with few species demonstrating reduced rates of rarity is opposite to that previously observed in mammals and birds. If the protection of representatives from a diversity of lineages is a conservation objective, plant conservation is facilitated by the fact that relatively few species-poor lineages contain rare species.     

Where the rare species are

Prioritizing geographic areas for conservation attention is important – time and money are in short supply but endangered species are not – and difficult. One popular perspective highlights areas with many species found nowhere else ( Myers et al. 2000 ). Another identifies areas that contain species with fewer close relatives elsewhere ( Faith 1992 ). One might characterize the first as focusing on geographic, and the second on phylogenetic, rarity. To the extent that geographically rare species are at greater risk of extinction ( Gaston & Fuller 2009 ), and that phylogenetically rare species contribute disproportionally to overall biodiversity ( Crozier 1997 ), it would seem reasonable to formally integrate the two approaches. In this issue, Rosauer et al. (2009) do just that; their elegant combined metric pinpoints areas missed out when the two types of rarity are looked at in isolation.     

The ecological drivers and consequences of wildlife trade

Wildlife trade is a key driver of extinction risk, affecting at least 24% of terrestrial vertebrates. The persistent removal of species can have profound impacts on species extinction risk and selection within populations. We draw together the first review of characteristics known to drive species use – identifying species with larger body sizes, greater abundance, increased rarity or certain morphological traits valued by consumers as being particularly prevalent in trade. We then review the ecological implications of this trade-driven selection, revealing direct effects of trade on natural selection and populations for traded species, which includes selection against desirable traits. Additionally, there exists a positive feedback loop between rarity and trade and depleted populations tend to have easy human access points, which can result in species being harvested to extinction and has the potential to alter source–sink dynamics. Wider cascading ecosystem repercussions from trade-induced declines include altered seed dispersal networks, trophic cascades, long-term compositional changes in plant communities, altered forest carbon stocks, and the introduction of harmful invasive species. Because it occurs across multiple scales with diverse drivers, wildlife trade requires multi-faceted conservation actions to maintain biodiversity and ecological function, including regulatory and enforcement approaches, bottom-up and community-based interventions, captive breeding or wildlife farming, and conservation translocations and trophic rewilding. We highlight three emergent research themes at the intersection of trade and community ecology: (1) functional impacts of trade; (2) altered provisioning of ecosystem services; and (3) prevalence of trade-dispersed diseases. Outside of the primary objective that exploitation is sustainable for traded species, we must urgently incorporate consideration of the broader consequences for other species and ecosystem processes when quantifying sustainability.     

Stag beetle fauna of Cambodia (Coleoptera: Lucanidae)

To date, no species catalogue of stag beetles (Lucanidae) has been compiled for Cambodia. According to the available literature, we assembled the checklist based on the previously recorded and recognized Cambodian lucanid species in the country. In the present paper, we newly record four species from Cambodia: Falcicornis axisopsis (Séguy, 1954); Neolucanus similis Bomans & Ratti, 1976; Prosopocoilus suturalis (Olivier, 1789); and Prosopocoilus jenkinsi (Westwood, 1848). An updated checklist of the Cambodian stag beetles is given. The total number of the Cambodian lucanid species has now reached 29, but this species count is considerably less diverse than those in neighboring countries. Our study suggested that this poor diversity is not primarily due to biogeography or small country size but to a lack of research effort.     

Drivers and interrelationships among multiple dimensions of rarity for freshwater fishes

Species can be rare or common in three different dimensions: geographic range size, habitat breadth, and local abundance. Understanding drivers of rarity are not only fundamentally interesting; it is also pertinent for their conservation. We addressed this challenge by analyzing the rarity of 291 native freshwater fishes occurring in ca 3500 independent stream reaches that span a broad environmental gradient across continental USA. Using phylogenetic regression and path analysis, we examined the concordance among the three rarity dimensions, and identified possible mechanisms by which species life‐history, habitat affinities, and biogeography drive variation in rarity. Weak double extinction jeopardies were driven by weakly positive correlations between habitat breadth and local abundance, and between habitat breadth and geographic range size. However, a triple extinction jeopardy was averted as local abundance and range size were not positively linked in our study. This is because large‐river and lacustrine habitat use mediated a trade‐off between local abundance and range size. Large rivers and lacustrine habitats represent important dispersal pathways and refugia that enabled fishes to acquire wide ranges; however, species using these habitats are less abundant overall because they are less adapted to small lotic channels, which comprise the majority of stream habitats in the US. Life‐history traits were key in governing the relationship between abundance and range size as large‐river and lacustrine habitat use were driven by body size, egg size, and parental care. Our analysis contributes novel insights into mechanisms that underlie multiple dimensions of rarity in freshwater fish and informs the prioritization of multiply rare species for conservation.