Historical Extinction Research Articles

Geographic differences in body size distributions underlie food web connectance of tropical forest mammals

Understanding variation in food web structure over large spatial scales is an emerging research agenda in food web ecology. The density of predator–prey links in a food web (i.e., connectance) is a key measure of network complexity that describes the mean proportional dietary breadth of species within a food web. Connectance is a critical component of food web robustness to species loss: food webs with lower connectance have been shown to be more susceptible to secondary extinctions. Identifying geographic variation in food web connectance and its drivers may provide insight into community robustness to species loss. We investigated the food web connectance of ground-dwelling tropical forest mammal communities in multiple biogeographic regions to test for differences among regions in food web connectance and to test three potential drivers: primary productivity, contemporary anthropogenic pressure, and variation in mammal body mass distributions reflective of historical extinctions. Mammal communities from fifteen protected forests throughout the Neo-, Afro-, and Asian tropics were identified from systematic camera trap arrays. Predator–prey interaction data were collected from published literature, and we calculated connectance for each community as the number of observed predator–prey links relative to the number of possible predator–prey links. We used generalized linear models to test for differences among regions and to identify the site level characteristics that best predicted connectance. We found that mammal food web connectance varied significantly among continents and that body size range was the only significant predictor. More possible predator–prey links were observed in communities with smaller ranges in body size and therefore sites with smaller body size ranges had higher mean proportional dietary breadth. Specifically, mammal communities in the Neotropics and in Madagascar had significantly higher connectance than mammal communities in Africa. This geographic variation in contemporary mammalian food web structure may be the product of historical extinctions in the Late Quaternary, which led to greater losses of large-bodied species in the Neotropics and Madagascar thus contributing to higher average proportional dietary breadth among the remaining smaller bodied species in these regions.

Coupled social and ecological change drove the historical extinction of the California grizzly bear (Ursus arctos californicus).

Large carnivores (order Carnivora) are among the world's most threatened mammals due to a confluence of ecological and social forces that have unfolded over centuries. Combining specimens from natural history collections with documents from archival records, we reconstructed the factors surrounding the extinction of the California grizzly bear (Ursus arctos californicus), a once-abundant brown bear subspecies last seen in 1924. Historical documents portrayed California grizzlies as massive hypercarnivores that endangered public safety. Yet, morphological measurements on skulls and teeth generate smaller body size estimates in alignment with extant North American grizzly populations (approx. 200 kg). Stable isotope analysis (δ13C, δ15N) of pelts and bones (n = 57) revealed that grizzlies derived less than 10% of their nutrition from terrestrial animal sources and were therefore largely herbivorous for millennia prior to the first European arrival in this region in 1542. Later colonial land uses, beginning in 1769 with the Mission era, led grizzlies to moderately increase animal protein consumption (up to 26% of diet), but grizzlies still consumed far less livestock than otherwise claimed by contemporary accounts. We show how human activities can provoke short-term behavioural shifts, such as heightened levels of carnivory, that in turn can lead to exaggerated predation narratives and incentivize persecution, triggering rapid loss of an otherwise widespread and ecologically flexible animal.

Biogeography and evolutionary history of Puntius sensu lato (Teleostei: Cyprinidae) in Sri Lanka

Sri Lanka’s biota is derived largely from Southeast Asian lineages which immigrated via India following its early-Eocene contact with Laurasia. The island is now separated from southeastern India by the 30 km wide Palk Strait which, during sea-level low-stands, was bridged by the 140 km-wide Palk Isthmus. Consequently, biotic ingress and egress were mediated largely by the climate of the isthmus. Because of their dependence on perennial aquatic habitats, freshwater fish are useful models for biogeographic studies. Here we investigate the timing and dynamics of the colonization of—and diversification on—Sri Lanka by a group of four closely-related genera of cyprinid fishes (Puntius sensu lato). We construct a molecular phylogeny based on two mitochondrial and two nuclear gene markers, conduct divergence timing analyses and ancestral-range estimations to infer historical biogeography, and use haplotype networks to discern phylogeographic patterns. The origin of Puntius s.l. is dated to ~ 20 Ma. The source of diversification of Puntius s.l. is Sri Lanka-Peninsular India. Species confined to perhumid rainforests show strong phylogeographic structure, while habitat generalists show little or no such structure. Ancestral range estimations for Plesiopuntius bimaculatus and Puntius dorsalis support an ‘Out of Sri Lanka’ scenario. Sri Lankan Puntius s.l. derive from multiple migrations across the Palk Isthmus between the early Miocene and the late Pleistocene. Species dependent on an aseasonal climate survived aridification in rainforest refugia in the island’s perhumid southwest and went on to recolonize the island and even southern India when pluvial conditions resumed. Our results support an historical extinction of Sri Lanka’s montane aquatic fauna, followed by a recent partial recolonization of the highlands, showing also that headwater stream capture facilitated dispersal across basin boundaries.

Conservation implications of a new fossil species of hopping-mouse, Notomys magnus sp. nov. (Rodentia: Muridae), from the Broken River Region, northeastern Queensland

The Australian hopping-mouse Notomys includes 10 species, eight of which are considered extinct, vulnerable, near-threatened or endangered. Here we report a new fossil species from the Broken River Region, northeastern Queensland. Notomys magnus sp. nov. is represented by craniodental material from late Quaternary cave deposits. It was a relatively large-bodied species of Notomys with a mass estimated to be ca 83 g. Notomys magnus sp. nov. is immediately distinguishable from the spinifex hopping-mouse (Notomys alexis), the northern hopping-mouse (Notomys aquilo), the fawn hopping-mouse (Notomys cervinus), the dusky hopping-mouse (Notomys fuscus), Mitchell’s hopping-mouse (Notomys mitchellii) and the big-eared hopping-mouse (Notomys macrotis) by its larger size (especially its longer upper molar crown length). Notomys magnus sp. nov. differs from the large-bodied Darling Downs hopping-mouse (Notomys mordax), long-tailed hopping-mouse (Notomys longicaudatus), short-tailed hopping-mouse (Notomys amplus) and broad-cheeked hopping-mouse (Notomys robustus) by possessing a unique first upper molar (M1) morphology including relatively well-developed buccal cusps, cusp T1 prominently isolated from T4, a relatively narrow posterior loph and an incipient anterior accessory cusp. Fossils of N. magnus sp. nov. are found in association with remains of several arid-adapted taxa, including the plains mouse (Pseudomys australis), the northern pig-footed bandicoot (Chaeropus yirratji), and N. longicaudatus, possibly indicating that N. magnus sp. nov. was also arid-adapted. Dating of fossil deposits containing N. magnus sp. nov. demonstrates that it was extant in the mid-Holocene (ca 8.5 ka) so it may have been still extant at the time of European colonization but suffered extinction soon after, mirroring the fate of similarly arid-adapted contemporaneous taxa (Chaeropus yirratji and N. longicaudatus). Historical extinctions in Notomys are biased towards larger species (N. amplus, N. longicaudatus and N. robustus), and the discovery of N. magnus sp. nov. adds further to that list. Given the already high number of extinct and endangered species within Notomys, the discovery of another member that suffered geologically recent extinction has conservation implications for modern critical weight range mammals (including other species of rodents) that are particularly susceptible to extinction. Most historical extinctions of critical weight range mammals were in southern and central Australia, but the discovery of N. magnus sp. nov. suggests that species in the tropical north also were detrimentally affected.Vikram Vakil [vikram.vakil@uqconnect.edu.au], School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia;Jonathan Cramb [jonathan.cramb@qm.qld.gov.au], Queensland Museum, Brisbane, Australia;Gilbert J. Price [g.price1@uq.edu.au], School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia;Gregory E. Webb [g.webb@uq.edu.au], School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia;Julien Louys [j.louys@griffith.edu.au], Australian Research Centre for Human Evolution, Griffith University, Brisbane, Queensland 4101, Australia.

Extinction in Public

AbstractThis essay argues that the concept of extinction, polysemous if not overdetermined, is becoming an emergent keyword of contemporary public life as it faces the climate crisis. To make this argument the essay critically considers the ways in which extinction is currently being made public—within and by the environmental humanities but also in the wider public sphere of political and cultural contestation. The essay begins by problematizing the concept of extinction itself, positing that it makes sense to think of the Sixth Extinction as the first historical extinction event—that is, as a social articulation of an organic process in which the causes and impacts are at once natural and social. Then the essay discusses the different extinction imaginaries that have operated across modernity, before finally turning to the writings of the Extinction Studies Working Group, whose conception of extinction as a process rather than event, and whose arguments that mass extinction presents an ethical call to responsibility, have become a template for how extinction is thought about within the field of the environmental humanities. The essay ends by posing some companionly criticisms of the extinction studies project.

Scott's Ghost-Seeing

Episodes of ghost-seeing radicalize a key device of Walter Scott’s historical novels, in which cultural difference submits to a developmental logic of historical difference. The spectral apparition signals not only the ghost-seer’s imminent death but also a historical extinction, that of the life-world in which supernatural phenomena count as real. This essay considers the complication of this historicist logic in The Bride of Lammermoor (1819) and The Monastery (1820). In the former, ghostliness is endemic to a time of pure liminality, unmoored from historical purpose: the suspension of the present between a past that fails to pass and a future that fails to arrive empties it of ontological substance. In The Monastery, the ghost rudely resists exorcism by rational explanation. Scott’s White Lady indexes the severity of the historical breach inflicted by the Protestant Reformation: a discontinuity more violent, in its impact upon knowledge, belief and the imagination, than revolutions of dynasties or political systems.

The ghost of hosts past: impacts of host extinction on parasite specificity.

A growing body of research is focused on the extinction of parasite species in response to host endangerment and declines. Beyond the loss of parasite species richness, host extinction can impact apparent parasite host specificity, as measured by host richness or the phylogenetic distances among hosts. Such impacts on the distribution of parasites across the host phylogeny can have knock-on effects that may reshape the adaptation of both hosts and parasites, ultimately shifting the evolutionary landscape underlying the potential for emergence and the evolution of virulence across hosts. Here, we examine how the reshaping of host phylogenies through extinction may impact the host specificity of parasites, and offer examples from historical extinctions, present-day endangerment, and future projections of biodiversity loss. We suggest that an improved understanding of the impact of host extinction on contemporary host–parasite interactions may shed light on core aspects of disease ecology, including comparative studies of host specificity, virulence evolution in multi-host parasite systems, and future trajectories for host and parasite biodiversity.This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.

Dark extinction: the problem of unknown historical extinctions.

The extinction of species before they are discovered and named (dark extinction, DE) is widely inferred as a significant part of species loss in the 'pre-taxonomic' period (approx. 1500-1800 CE) and, to some extent, in the 'taxonomic period' (approx. 1800-present) as well. The discovery of oceanic islands and other pristine habitats by European navigators and the consequent introduction of destructive mammals, such as rats and goats, started a process of anthropogenic extinction. Much ecosystem change happened before systematic scientific recording, so has led to DE. Statistical methods are available to robustly estimate DE in the 'taxonomic period'. For the 'pre-taxonomic period', simple extrapolation can be used. The application of these techniques to world birds, for example, suggests that approximately 56 DEs occurred in the 'taxonomic period' (1800-present) and approximately 180 in the 'pre-taxonomic period' (1500-1800). Targeting collection activities in extinction hotspots, to make sure organisms are represented in collections before their extinction, is one way of reducing the number of extinct species without a physical record (providing that collection efforts do not themselves contribute to species extinction).

Extinction Dynamics Under Extreme Conservation Threat: The Flora of St Helena

The flora of the island of St Helena provides an amplified system for the study of extinction by reason of the island’s high endemism, small size, vulnerable biota, length of time of severe disturbance (since 1502) and severity of threats. Endemic plants have been eliminated from 96.5% of St Helena by habitat loss. There are eight recorded extinctions in the vascular flora since 1771 giving an extinction rate of 581 extinctions per million species per year (E/MSY). This is considerably higher than background extinction rates, variously estimated at 1 or 0.1 E/MSY. We have no information for plant extinctions prior to 1771 but applying the same extinction rate to the period 1502 to 1771 suggests that there may be around ten unrecorded historical extinctions. We use census data and population decline estimates to project likely extinction forward in time. The projected overall extinction rate for the next 200 years is somewhat higher at 625 E/MSY. However, our data predict an extinction crunch in the next 50 years with 4 species out of the remaining 48 likely to become extinct during this period. It is interesting that during a period when the native plant areas dropped to 3.5% of the original, the extinction rate appears to have remained shallowly linear with under 30% of the endemic flora becoming extinct.

Exhibiting Extinction: Martha and the Monument, Two Modes of Remembering Nature

Whether stuffed remains in a museum case, inscribed tombstone, or stone wall perched on a cliff, memorials to extinct animals are timestamps representing human-animal relationships at particular moments in time. This essay analyzes the rhetoric and imagery of historical extinctions as seen in these memorials to understand the ways people struggled to understand the loss. Through examination of memorials to extinct species in U.S. museums, parks, and zoos my research has revealed a continuous struggle to identify the personhood of animals, define human-animal interactions, and locate human responsibility for environmental change.
 
 While each memorial mimics remembrance practices used for humans and human events, they differ in their acknowledgement of the individuality and the agency of its extinction which, in turn, often denies agency to the animal. Steeped as they are in Romantic-era notions of wildness, these memorials can be read as parables of environmentalism, but in their conceptualization of the animal, they instruct us in the varieties of human-animal interactions and representations within the environmental movement at different times and places, making them more complex spaces than their simplicity suggests. While memorials present only a slice of the story, the memories they create and reinforce become part of the cultural ways of dealing with extinction that is often more popular and more poignant than historical narratives documenting their declines. At its core, my research adds to the literature on constructions of Nature in American culture by connecting 19th-century declension narratives with 20th-century extinctions, and problematizes the American ideology of abundance.

Research applications of primary biodiversity databases in the digital age.

Our world is in the midst of unprecedented change—climate shifts and sustained, widespread habitat degradation have led to dramatic declines in biodiversity rivaling historical extinction events. At the same time, new approaches to publishing and integrating previously disconnected data resources promise to help provide the evidence needed for more efficient and effective conservation and management. Stakeholders have invested considerable resources to contribute to online databases of species occurrences. However, estimates suggest that only 10% of biocollections are available in digital form. The biocollections community must therefore continue to promote digitization efforts, which in part requires demonstrating compelling applications of the data. Our overarching goal is therefore to determine trends in use of mobilized species occurrence data since 2010, as online systems have grown and now provide over one billion records. To do this, we characterized 501 papers that use openly accessible biodiversity databases. Our standardized tagging protocol was based on key topics of interest, including: database(s) used, taxa addressed, general uses of data, other data types linked to species occurrence data, and data quality issues addressed. We found that the most common uses of online biodiversity databases have been to estimate species distribution and richness, to outline data compilation and publication, and to assist in developing species checklists or describing new species. Only 69% of papers in our dataset addressed one or more aspects of data quality, which is low considering common errors and biases known to exist in opportunistic datasets. Globally, we find that biodiversity databases are still in the initial stages of data compilation. Novel and integrative applications are restricted to certain taxonomic groups and regions with higher numbers of quality records. Continued data digitization, publication, enhancement, and quality control efforts are necessary to make biodiversity science more efficient and relevant in our fast-changing environment.

Insights from 180 years of mitochondrial variability in the endangered Mediterranean monk seal (Monachus monachus)

AbstractMediterranean monk seals (MMS) are among the most endangered marine mammals on Earth. We screened mitochondrial variability (control region [CR1] and mitogenomes) of the species through a 180‐yr timeframe and extended by 20% (n = 205) the number of samples from a previous investigation, including historical specimens from 1833 to 1975. Although we detected two new, rare CR1 haplotypes, genetic diversity remained extremely low. Fully resolved haplotype median network and rarefaction analysis both suggested low probability for further unscreened haplotypes. There was no clear phylogeographic structure across the 12 marine subdivisions covered by the species’ range. Haplotypes previously considered diagnostic of the extant North Atlantic and eastern Mediterranean populations had their distributions extended into the western Mediterranean and the North Atlantic, respectively, by both historical and recent samples. Our study suggests that MMS have been genetically depauperate since at least the mid‐19th century, and that the massive 1997 die‐off in Western Sahara (North Atlantic) could have caused local haplotype extinctions. Our results support the hypothesis of past metapopulation dynamics across the species range, where the current segregation into geographically distant and genetically depauperate breeding populations (i.e., North Atlantic and eastern Mediterranean Sea) derives from the combined effects of historical extinctions, genetic drift on small breeding groups, and persistently low levels of genetic diversity.

Local extinctions of insular avifauna on the most remote inhabited island in the world

The overwhelming majority of avian extinctions have occurred on islands, where introduced predators, habitat loss, disease, and human persecution have resulted in the loss of over 160 species in the last 500 years. Understanding the timing and causes of these historical extinctions can be beneficial to identifying and preventing contemporary biodiversity loss, as well as understanding the nature of island ecosystems. Tristan da Cunha (henceforth “Tristan”), the most remote inhabited island in the world, has lost three species from the main island since permanent human settlement in 1811—the Tristan Moorhen (Gallinula nesiotis), Inaccessible Finch (Nesospiza acunhae acunhae), and Tristan Albatross (Diomedea dabbenena). We used recently developed Bayesian methods, and sightings of mixed certainty compiled from historical documents, to estimate the extinction date of these three species from Tristan based on specimens. We estimate that all three species were likely extirpated from Tristan between 1869 and 1880 following a period of significant habitat alteration and human overexploitation, and only the albatross had a high probability of persistence when Black Rats (Rattus rattus) arrived in 1882, the previously assumed cause of extinction for all three species. Better estimates of extinction dates are essential for understanding the causes of historical biodiversity loss, and the combination of historical ecology with modern statistical methods has given us novel insights into the timing and therefore the causes of extinctions on one of the most isolated islands in the world.

Long-term archives reveal shifting extinction selectivity in China's postglacial mammal fauna

Ecosystems have been modified by human activities for millennia, and insights about ecology and extinction risk based only on recent data are likely to be both incomplete and biased. We synthesize multiple long-term archives (over 250 archaeological and palaeontological sites dating from the early Holocene to the Ming Dynasty and over 4400 historical records) to reconstruct the spatio-temporal dynamics of Holocene–modern range change across China, a megadiverse country experiencing extensive current-day biodiversity loss, for 34 mammal species over three successive postglacial time intervals. Our combined zooarchaeological, palaeontological, historical and current-day datasets reveal that both phylogenetic and spatial patterns of extinction selectivity have varied through time in China, probably in response both to cumulative anthropogenic impacts (an ‘extinction filter’ associated with vulnerable species and accessible landscapes being affected earlier by human activities) and also to quantitative and qualitative changes in regional pressures. China has experienced few postglacial global species-level mammal extinctions, and most species retain over 50% of their maximum estimated Holocene range despite millennia of increasing regional human pressures, suggesting that the potential still exists for successful species conservation and ecosystem restoration. Data from long-term archives also demonstrate that herbivores have experienced more historical extinctions in China, and carnivores have until recently displayed greater resilience. Accurate assessment of patterns of biodiversity loss and the likely predictive power of current-day correlates of faunal vulnerability and resilience is dependent upon novel perspectives provided by long-term archives.

Biodiversity and conservation of Cuban mammals: past, present, and invasive species

Land mammals of the Caribbean Islands biodiversity hotspot have suffered a high rate of extinction since human arrival, principally in the last 500 years since colonialism began. Here, we present an extensive review and bibliography of this topic in Cuba, including details regarding the surviving endemic species of volant and terrestrial mammals and locations of species on 121 protected areas. We analyzed patterns of species richness, endemism, body mass, diet, habitat, geographic distribution of the observed richness, conservation threats, and possible causes and threats to future extinction. Cuban mammal biodiversity is comprised of 59 native species, 24 extinct species and 35 extant species, most of which are endemic to the Cuban archipelago. We compared the threats of habitat destruction and hunting, with emphasis on invasive mammal species as drivers of historical extinction in Cuba. A total of 44 mammal species have been introduced since 1509, with 33 invasive species living in the wild and exerting differing degrees of impact, principally by predation and competition. Additionally, we evaluated interactions among invasive and native mammals, emphasizing predation of feral cats upon Solenodon cubanus, Capromys pilorides, and other small endemic vertebrates as determined from analyses of scat contents. We found that black rats (Rattus rattus) reach densities of 147–322 individuals/ha in Solenodon habitat, thus likely are major competitors for food and refuges to these evolutionarily distinct and endangered Cuban mammals.Version of Record, with fixed content and layout in compliance with Art. 8.1.3.2 ICZN.

Diversification of the rainfrog Pristimantis ornatissimus in the lowlands and Andean foothills of Ecuador.

Geographic barriers and elevational gradients have long been recognized as important in species diversification. Here, we illustrate an example where both mechanisms have shaped the genetic structure of the Neotropical rainfrog, Pristimantis ornatissimus, which has also resulted in speciation. This species was thought to be a single evolutionary lineage distributed throughout the Ecuadorian Chocó and the adjacent foothills of the Andes. Based on recent sampling of P. ornatissimus sensu lato, we provide molecular and morphological evidence that support the validity of a new species, which we name Pristimantis ecuadorensis sp. nov. The sister species are elevational replacements of each other; the distribution of Pristimantis ornatissimus sensu stricto is limited to the Ecuadorian Chocó ecoregion (< 1100 m), whereas the new species has only been found at Andean localities between 1450–1480 m. Given the results of the Multiple Matrix Regression with Randomization analysis, the genetic difference between P. ecuadorensis and P. ornatissimus is not explained by geographic distance nor environment, although environmental variables at a finer scale need to be tested. Therefore this speciation event might be the byproduct of stochastic historic extinction of connected populations or biogeographic events caused by barriers to dispersal such as rivers. Within P. ornatissimus sensu stricto, morphological patterns and genetic structure seem to be related to geographic isolation (e.g., rivers). Finally, we provide an updated phylogeny for the genus, including the new species, as well as other Ecuadorian Pristimantis.

Stephen Jay Gould and the Value of Neutrality of Science During the Cold War

Stephen Jay Gould was a paleontologist and scientific celebrity at the close of the twentieth century, most famous for his popular writings on evolution and his role in the American creationist controversies of that era. In the early 1980s, Gould was drawn into the "nuclear winter" episode through his friendship with Carl Sagan, an astronomer and popular science celebrity. Sagan helped develop the theory of nuclear winter and subsequently used the theory as evidence to petition the United States government to scale back its nuclear armament. The theory of nuclear winter claimed that even a small nuclear exchange could result in a atmospheric blackening akin to the extinction event of the late Cretaceous. Gould was not a climate scientist but he testified before the U.S. House of Representatives as an expert on historical extinction events. Gould's insistence on the value-neutrality of nuclear winter reveals much about the moral politics of science in late Cold War America. Coming at the heels of leftist scientific activism of the 1980s, the nuclear winter episode demonstrates how value-neutrality emerged the salient feature of scientific involvement in American politics in this period.

The changing role of mammal life histories in Late Quaternary extinction vulnerability on continents and islands.

Understanding extinction drivers in a human-dominated world is necessary to preserve biodiversity. We provide an overview of Quaternary extinctions and compare mammalian extinction events on continents and islands after human arrival in system-specific prehistoric and historic contexts. We highlight the role of body size and life-history traits in these extinctions. We find a significant size-bias except for extinctions on small islands in historic times. Using phylogenetic regression and classification trees, we find that while life-history traits are poor predictors of historic extinctions, those associated with difficulty in responding quickly to perturbations, such as small litter size, are good predictors of prehistoric extinctions. Our results are consistent with the idea that prehistoric and historic extinctions form a single continuing event with the same likely primary driver, humans, but the diversity of impacts and affected faunas is much greater in historic extinctions.

Millennial-scale faunal record reveals differential resilience of European large mammals to human impacts across the Holocene.

The use of short-term indicators for understanding patterns and processes of biodiversity loss can mask longer-term faunal responses to human pressures. We use an extensive database of approximately 18 700 mammalian zooarchaeological records for the last 11 700 years across Europe to reconstruct spatio-temporal dynamics of Holocene range change for 15 large-bodied mammal species. European mammals experienced protracted, non-congruent range losses, with significant declines starting in some species approximately 3000 years ago and continuing to the present, and with the timing, duration and magnitude of declines varying individually between species. Some European mammals became globally extinct during the Holocene, whereas others experienced limited or no significant range change. These findings demonstrate the relatively early onset of prehistoric human impacts on postglacial biodiversity, and mirror species-specific patterns of mammalian extinction during the Late Pleistocene. Herbivores experienced significantly greater declines than carnivores, revealing an important historical extinction filter that informs our understanding of relative resilience and vulnerability to human pressures for different taxa. We highlight the importance of large-scale, long-term datasets for understanding complex protracted extinction processes, although the dynamic pattern of progressive faunal depletion of European mammal assemblages across the Holocene challenges easy identification of ‘static’ past baselines to inform current-day environmental management and restoration.

The colonisation of exotic species does not have to trigger faunal homogenisation: lessons from the assembly patterns of arthropods on oceanic islands.

Human-caused disturbances can lead to the extinction of indigenous (endemic and native) species, while facilitating and increasing the colonisation of exotic species; this increase can, in turn, promote the similarity of species compositions between sites if human-disturbed sites are consistently invaded by a regionally species-poor pool of exotic species. In this study, we analysed the extent to which epigean arthropod assemblages of four islands of the Azorean archipelago are characterised by nestedness according to a habitat-altered gradient. The degree of nestedness represents the extent to which less ubiquitous species occur in subsets of sites occupied by the more widespread species, resulting in an ordered loss/gain of species across environmental or ecological gradients. A predictable loss of species across communities while maintaining others may lead to more similar communities (i.e. lower beta-diversity). In contrast, anti-nestedness occurs when different species tend to occupy distinct sites, thus characterising a replacement of species across such gradients. Our results showed that an increase in exotic species does not promote assemblage homogenisation at the habitat level. On the contrary, exotic species were revealed as habitat specialists that constitute new and well-differentiated assemblages, even increasing the species compositional heterogeneity within human-altered landscapes. Therefore, contrary to expectations, our results show that both indigenous and exotic species established idiosyncratic assemblages within habitats and islands. We suggest that both the historical extinction of indigenous species in disturbed habitats and the habitat-specialised character of some exotic invasions have contributed to the construction of current assemblages.