Peak In Richness Research Articles

Bat diversity along an altitudinal gradient in the Itabapoana drainage basin, Espírito Santo state, Brazil

Entre os mamíferos que ocorrem ao longo de todo gradiente altitudinal em montanhas no sudeste do Brasil (i.e. Mata Atlântica), os morcegos podem ser um excelente modelo de análise, porque são abundantes e apresentam todas as guildas. Nas cadeias de montanhas ao redor do mundo, a comunidade de morcegos pode apresentar dois padrões de riqueza e diversidade de espécies: 1) declínio progressivo na riqueza e diversidade de espécies à medida que a altitude aumenta; ou 2) um pico de riqueza e diversidade no nível altitudinal intermediário. Nesse contexto, o presente estudo teve como objetivo realizar um levantamento das espécies de morcegos ocorrentes nos fragmentos localizados na bacia do rio Itabapoana verificando a influência do gradiente altitudinal nas taxas de capturas dos morcegos. Para a captura dos morcegos, utilizamos redes de neblina, armadas no nível do solo, totalizando um esforço amostral de 1.500 m2/ha para cada localidade. A região do rio Itabapoana apresentou uma elevada riqueza de espécies de morcegos (26 espécies), abrigando 44% das espécies já registradas no Espírito Santo. Nosso estudo mostrou que existe uma variação nas taxas de captura de morcegos e riqueza de espécies, com uma reposição de algumas espécies, ao longo do gradiente altitudinal na região do rio Itabapoana. As mudanças na heterogeneidade do habitat ao longo desse gradiente são provavelmente um dos fatores ecológicos fortes que afetam esses parâmetros. Além disso, os dados desse estudo permitem a expansão do conhecimento das espécies de morcegos que ocorrem na região do Itabapoana. A diversidade de espécies encontrada, juntamente com a ocorrência de espécies raras, destaca a importância da região para a conservação ajudando a entender os padrões de distribuição das espécies.

If Higher Pay Is Profitable, Why Is It So Rare? Modeling Competing Strategies in Mass Market Services

Several case studies suggest that firms targeting mass market services can align profitability with jobs offering a living wage, stable schedules, and engaging work. Yet, few do. To understand this puzzle, we draw on theories of firms as systems of interdependent choices. Building on a few cases, we map the processes connecting managerial choice to performance and formalize the resulting performance landscape. In a strategy space defined by two dimensions—task richness and compensation—two local profitability peaks emerge: one with low compensation and low task richness and one with high compensation and high task richness. The bimodal landscape results from complementarity among choices and is robust when the strategy space is expanded from two to six dimensions and under many alternative parameterizations. Exploring how firms discover, move to, and remain at the high-compensation–high-task richness peak, we find three challenges to this strategy: (a) contextuality—adoption, imitation, and replication are harder for strategies that rely on interdependences among components and thus, require significant customization for each context; (b) temporal complexity—strategies depending on long-term and synergistic investments and slow-moving reinforcing feedbacks are hard to learn owing to misleading performance feedback; and (c) variable demand with no inventory buffers—efforts to adjust labor supply to highly variable demand in services often lead to unstable schedules given with short notice that drive quality employees away and compromise the strategy. These mechanisms can undermine promising strategies even if the actual performance landscape includes a small number of local peaks.

Least speciose among the most speciose: Natural history correlates of monospecific and bispecific genera of Rodentia and Soricomorpha.

Monospecific and bispecific genera are of special concern as they represent unique phylogenetic/evolutionary trajectories within larger clades. In addition, as phylogenetically older taxa are supposed to be exposed to higher rarity and extinction risk, monospecific and bispecific genera may be intrinsically more prone to extinction risks than multispecies genera, although extinction risks also depend on the ecological and biological strategy of the species. Here, the distribution across biogeographical zones and the levels of threat to 2 speciose orders of mammals (monospecific and bispecific genera of Rodentia and Soricomorpha) are investigated in order to highlight major patterns at the worldwide scale. In Rodentia, 39.7% of the genera (n = 490) were monospecific and 17.9% were bispecific. In Soricomorpha, 44.4% of the total genera (n = 45) were monospecific and 15% were bispecific. There was a positive correlation between the number of monospecific genera and the total number of genera per family. Peaks of monospecific and bispecific genera richness were observed in Neotropical, Oriental and Afrotropical regions in rodents and in the Palearctic region in soricomorphs. Range size was significantly uneven across biogeographic region in rodents (with larger ranges in Nearctic and Oriental regions and smaller ranges in the Australian region), but there was no difference across biogeographic regions in terms of range size in soricomorphs. Most of the monospecific and bispecific genera occurred in forest habitat in both taxa. The frequency distribution of the monospecific and bispecific genera across IUCN categories did not differ significantly from the expected pattern using the total rodent genera and the multispecies genera.

Eocene ctenodactyloid rodent assemblages and diversification from Erden Obo, Nei Mongol, China

New ctenodactyloid occurrences (Yuomys magnus sp. nov., Gobiomys neimongolensis and Gobiomys exiguus) from the ‘Lower Red’ to the ‘Upper Red’ beds of the Erden Obo section in Nei Mongol, China are reported. Here, we present an updated review of the ctenodactyloid rodents from the Erden Obo section. We have recognised eight species and one indeterminate species belonging to six genera: Advenimus, Chenomys, Gobiomys, Tamquammys, Simplicimys, and Yuomys. The ctenodactyloids show an initial burst in diversification in the upper part of the ‘Basal Red’ of the early Eocene. A maximum richness peak is present at the lower part of the ‘Basal White’ which falls near the boundary of early and middle Eocene. Gobiomys, the only surviving genus from the ‘Middle Red’ to the ‘Upper Red’ beds, shows that the diversity of ctenodactyloids declined rapidly after late middle Eocene. Based on the study of the abundant ctenodactyloid rodents, we recognise some evolutionary tendencies among Eocene ctenodactyloids.http://www.zoobank.org/urn:lsid:zoobank.org:act:33D2442E-DA27-494A-80CB-2DB9DA9E4E1A

Patterns and underlying mechanisms of non-volant small mammal richness along two contrasting mountain slopes in southwestern China

The species richness patterns of small mammals and the processes shaping them in two gradients of a mountain with different spatial and climatic characteristics were examined using standard sampling scheme. We trapped 2,006 small mammals representing 37 species, along elevational gradients on both western and eastern slopes of the Ailao Mountains, Southwest China. Using mid-domain effect model, model selection and model averaging, we examined the effects of slope, area, mean annual temperature (MAT), mean annual humidity (MAH), productivity, plant species richness (PSR) and the mid-domain effect (MDE) on the patterns of small mammal diversity. The hump-shaped patterns were favored along the elevational gradient, but shapes of diversity curves were different on the contrasting slopes. Area and productivity were the most important factors in explaining the variation of total species richness. However, for each specific group of small mammals (i.e. insectivores vs. rodents, large-ranged vs. small-ranged species, endemic vs. non-endemic species), the peaks of species richness and their primary drivers varied. The major explanatory factors for richness pattern of each small mammal group were not significantly different between the slopes, suggesting the existence of the general underlying mechanisms on two slopes of a mountain.

Contrasting patterns of altitudinal distribution between parasitoid wasps of the subfamilies Braconinae and Doryctinae (Hymenoptera: Braconidae)

Abstract Many tropical organisms have narrow altitudinal ranges and therefore may be especially vulnerable to climate change. Parasitoid wasps are no exception, so baseline knowledge about their vulnerability to rising temperatures needs to include analyses of their distributional ranges along elevational gradients. Using museum collections of the parasitoid subfamilies Braconinae and Doryctinae (Hymenoptera: Braconidae) from Costa Rica, we tested two alternative hypotheses explaining altitudinal distributions of communities: (i) the Mid‐domain effect, which states that species diversity peaks at middle elevations as a result of species’ random distributions; and (ii) Rapoport's effect, which predicts that species diversity should monotonically decrease with increasing elevation. We found that for the Doryctinae, species diversity decreased monotonically with elevation, while the Braconinae showed two peaks. Species altitudinal ranges increased with elevation in the Doryctinae, as predicted by Rapoport's effect, but not so in the Braconinae. Neither of the subfamilies’ distributions fit the prediction of the Mid‐domain effect. The richness peak at low elevations displayed by the Braconinae and Doryctinae matches the distribution of wood‐boring beetles, which are potential hosts for both taxa. The second peak described in the Braconinae at middle elevations may reflect either better access or higher availability of potential hosts in the Diptera and Lepidoptera at those elevations. Because species in the Doryctinae, on average, had altitudinal ranges that were broader and lower in elevation than species in the Braconinae, our results suggest that species in the Doryctinae might have greater resilience to future temperature increases.

Monitoring fruit-feeding butterfly assemblages in two vertical strata in seasonal Atlantic Forest: temporal species turnover is lower in the canopy

Abstract:To address how seasonality affects the richness and abundance of tropical insects, we compared the canopy and understorey communities of fruit-feeding butterflies in a seasonal Atlantic forest in south-eastern Brazil. Butterflies were sampled over 1 y using a standardized design with baited traps. A total of 2047 individuals in 69 species were recorded (1415 in the canopy, 632 in the understorey). Clear differences were found between canopy and understorey, with significantly higher butterfly abundances in the canopy. We observed two marked peaks of abundance and richness in both strata; one at the transition from dry to the wet seasons, and the other at the transition from wet to dry seasons. We found lower species turnover throughout the year in the canopy. We interpret this as evidence that temperature is more important than rainfall in explaining the yearly variation of abundance in vertical strata. The higher temperatures found in the canopy may allow butterflies to maintain activity in this stratum all year round, whereas the understorey is subject to colder temperatures, thus presenting a higher species turnover. These results improve our understanding of diversity gradients between evergreen and seasonal tropical forests, allowing insights into how climate and beta diversity gradients interact.

Are epiphytic bryophyte communities characterized by changes along an elevational gradient?—A preliminary study on eastern Viti Levu, Fiji Islands

A comparative study of epiphytic bryophytes on tree trunks was undertaken in three principal vegetation types along an elevational gradient on the windward wet side of the largest island in Fiji, Viti Levu. This ecological study is the first of its kind for Fiji and the islands of the South Pacific and it serves as groundwork for any future ecological research in the region for bryophytes. This study set out to test if elevational range of study sites and height along host tree stem influenced bryophyte species diversity and distribution in Fiji. This was done by assessing bryophyte species presence/absence on the lower stems of the Calophyllum spp. trees and tree fern species at three elevations (~160 m, 590 m, and 1260 m). There were two main findings that emerged from this preliminary assessment. Firstly, there was a hump-shaped distribution of bryophyte diversity with a peak of species richness observed at mid-elevation or in the upland forest; with a dominance of liverworts at each of the three elevations. Secondly, the bryophyte communities showed good separation at both host tree level and at the site level, reflecting the ecological differences between the different host trees and between the three sites along the elevational gradient. The results from this survey alone suggest the need for priority to be given to upland forest protection and conservation. It also demonstrates the usefulness of bryophyte communities in discerning vegetation of different environmental and microclimatic conditions along an elevational gradient.

Functional diversity response to hardwood forest management varies across taxa and spatial scales.

Contemporary forest management offers a trade-off between the potential positive effects of habitat heterogeneity on biodiversity, and the potential harm to mature forest communities caused by habitat loss and perforation of the forest canopy. While the response of taxonomic diversity to forest management has received a great deal of scrutiny, the response of functional diversity is largely unexplored. However, functional diversity may represent a more direct link between biodiversity and ecosystem function. To examine how forest management affects diversity at multiple spatial scales, we analyzed a long-term data set that captured changes in taxonomic and functional diversity of moths (Lepidoptera), longhorned beetles (Coleoptera: Cerambycidae), and breeding birds in response to contemporary silvicultural systems in oak-hickory hardwood forests. We used these data sets to address the following questions: how do even- and uneven-aged silvicultural systems affect taxonomic and functional diversity at the scale of managed landscapes compared to the individual harvested and unharvested forest patches that comprise the landscapes, and how do these silvicultural systems affect the functional similarity of assemblages at the scale of managed landscapes and patches? Due to increased heterogeneity within landscapes, we expected even-aged silviculture to increase and uneven-aged silviculture to decrease functional diversity at the landscape level regardless of impacts at the patch level. Functional diversity responses were taxon-specific with respect to the direction of change and time since harvest. Responses were also consistent across patch and landscape levels within each taxon. Moth assemblage species richness, functional richness, and functional divergence were negatively affected by harvesting, with stronger effects resulting from uneven-aged than even-aged management. Longhorned beetle assemblages exhibited a peak in species richness two years after harvesting, while functional diversity metrics did not differ between harvested and unharvested patches and managed landscapes. The species and functional richness of breeding bird assemblages increased in response to harvesting with more persistent effects in uneven- than in even-aged managed landscapes. For moth and bird assemblages, species turnover was driven by species with more extreme trait combinations. Our study highlights the variability of multi-taxon functional diversity in response to forest management across multiple spatial scales.

Depth diversity profile of polychaete worms in Bahía Chatham, Isla del Coco National Park, Costa Rican Pacific

The subtidal benthos of tropical islands has been poorly studied in the Eastern Tropical Pacific. Several studies have been published on taxonomic collections from oceanic islands in the region, but ecological features and community structure are practically unknown. In the present study, composition of the polychaete community along a depth gradient from the sand bottom of Bahía Chatham, Isla del Coco National Park, Costa Rica is analyzed. Fifty species of polychaetes belonging to 28 families were found. There is a peak in diversity, abundance and richness at 28-30m. The lowest values occurred at 50m depth with values increasing below this depth. The composition of species changed with depth with some species being found only at depths either less than or greater than 50m. This pattern can be explained in part by the location of the thermocline that occurred at around 50m depth. Citation: Sibaja-Cordero, J.A., J. Cortés & H.K. Dean. 2012. Depth diversity profile of polychates worms in Bahía Chatham, Isla del Coco National Park, Pacific of Costa Rica. Rev. Biol. Trop. 60 (Suppl. 3): 293-301. Epub 2012 Dec 01.

Elevational seed plants richness patterns in Bhutan, Eastern Himalaya

AbstractAimWe used published data of the floristic and elevational distribution of seed plants of Bhutan to test the contribution of climatic, topographical and biogeographical variables to shape elevational species richness and endemism patterns.LocationBhutan.MethodsWe compiled data of seed plant species distributions from the Flora of Bhutan and related them to energy, humidity, and topographically related variables and biogeographical distributions. We used multiple regression models to identify most predictive independent variables by multi‐model‐inference based on AICc.ResultsWe find highest species richness at mid elevations (1500–2000 m), while endemic richness peaks markedly higher at 4500 m. Separated for life forms, the peak of richness shifts upward along the elevational gradient in the order of trees – shrubs – herbs – graminoids. Elevational richness peaks of temperate taxa were centred at high and of tropical taxa at low elevations. Temperature was identified as most influential for species richness patterns and showed a humped relationship to richness patterns.Main conclusionsThe humped patterns of species richness in Bhutan correspond to results from other studies in low latitude mountains, and the correlation of these patterns to energy driven variables, especially temperature, can be confirmed. The humped relationship of temperature (including water regimes driven by temperature) to richness indicates elevation zones of moderate temperatures with absence of temperature extremes as predicting species richness, and the high elevation peak of endemism may be related to mountain terrain configuration and climatic history. The different elevations of richness peaks of tropical and temperate taxa underlines the notion of a transition zone between temperate and tropical realms, thus the intermingling of different evolutionary histories. For further research, we require fine scale local data for detailed taxa distributions in order to infer issues from evolutionary processes in landscape development to identify target regions for conservation purposes.

Diversification rates in Ctenodactylidae (Rodentia, Mammalia) from Mongolia

Gundis, or comb rats, are rodents of the family Ctenodactylidae. Extant gundis are restricted to Africa and represent a vestige of the diversity that the ctenodactylids attained at both palaeoecological and palaeobiogeographical levels. Here, we present an updated review of the Ctenodactylidae from the Valley of Lakes, Mongolia, based on the study of large collections now available. We have recognised 13 valid species of ctenodactylids grouped into five genera: Karakoromys, Huangomys, Tataromys, Yindirtemys, and Prodistylomys. The ctenodactylids show an initial burst in diversification in the early Oligocene followed by a sequential generic extinction of Karakoromys, Huangomys, and Tataromys. A maximum richness peak at the late Oligocene was followed by a profound diversity crisis. Yindirtemys, the only surviving genus, persisted into the Miocene, joining three Prodistylomys species. These last representatives of the group disappeared coinciding with the late Xiejian faunal reorganisation (Mongolian biozone D).

Modelling present and future global distributions of razor clams (Bivalvia: Solenidae)

Razor clams (Pharidae and Solenidae) are deep-burrowing bivalves that inhabit shallow waters of the tropical, subtropical, and temperate seas. Using ‘maximum entropy’, a species distribution modelling software, we predicted the most suitable environments for the entire family and 14 Solen species to indicate their present and future geographic distributions. Distance to land, depth, and sea surface temperature (SST) were the most important environmental variables in training and creating the present and future distribution models both at the family and species level. In the present distribution models at the family level, the most suitable environment was where distance to land was between 0 and 100 km, a depth of 0–150 m, wave height of 5–7 m, a mean chlorophyll-a concentration about 0.7 mg m−3, and mean SST between 12 and 28 °C. Comparison with the future distribution models at the species level, found that most species were predicted to shift their distribution ranges poleward under the future environmental scenarios; i.e. species in the northern hemisphere would shift northward and southern species southward. Models also predicted that half of the species would expand their distribution ranges, 29% of species would not change their distribution, and 21% of species would shrink their distribution ranges under future climate change. Expanding geographic ranges would result in overlap in species ranges and thus greater species richness at regional scales. Model results predict that the mid-latitude peaks of species richness will move further apart, increasing the dip in richness near the equator, due to global climate change.

A decadal review of urban ornithology and a prospectus for the future

The study of urban birds has increased exponentially in the last century. A prior review of the scientific literature up to the year 2000 found 100 research articles on urban birds, but in the past decade alone, over 1000 have been published. Here I review the studies from 2006–2015 to characterize their approach, location, general findings and recent obsessions, with an eye toward suggesting important future directions. Urban ornithology remains centred in the northern hemisphere, although there is a rapid increase in studies from southern, tropical and biodiverse settings. Studies in the north have changed from documentation of the composition of urban avifaunas to include many studies of the demographic response to aspects of urban environments. Studies of pattern remain most common in Latin America, Asia, Africa, New Zealand and the Middle East. Across the world, ornithologists are revealing the rapid evolution of behavioural and morphological adaptations by birds to the urban environment, much of which is due to phenotypic plasticity. The relationship of humans to nature generally and birds specifically has been increasingly studied as a driver of avifaunal change as well as a factor affecting human ethics. Urban ornithology remains rarely experimental, but it has matured to the point of supporting synthetic reviews and meta‐analyses that quantify the loss of avian diversity from city centres, characterize successful urban birds, discuss the role of amount and arrangement of vegetation on bird life, and explore the complex relationships between the subsidies and hazards of urban life and the survival and reproduction of birds. Yet much remains to be learned, including how some species thrive in cities with abundant predators; how city form and location affect the peak in avian richness that occurs typically at intermediate levels of urbanization; the significance of functional biotic homogenization; and the ways in which engaging citizens in urban bird life informs their broader environmental land ethic.

Sediment type rules the response of aquatic plant communities to dewatering in wetlands

AbstractQuestionsThe effect of dewatering on aquatic plant communities may vary with sediment properties, such as particle size and organic matter content, as both control water retention in the sediment during dewatering. No study has tested how sediment type affects the short‐term response of plant communities to dewatering. We hypothesized that for the same dewatering event: (1) organic, silt and coarse sediments rank along a gradient of water deficit, with which community resistance and resilience decrease; (2) species survival during the event depend on their known ecological affinity for water; and (3) a peak in species richness associated with an intermediate water deficit occurs in silty habitats.LocationRiverine wetlands in the floodplain of the Ain River, France.MethodsEighteen sampling units were defined, set over three sediment types: gravel‐dominated coarse sediment, silt and organic matter‐dominated sediment. For each sediment type, three sampling units were permanently aquatic, and three sampling units underwent summer dewatering. A survey of species cover was conducted in each sampling unit at four times: before summer dewatering, at the beginning of the event, at the end of the event and 2 months after rewetting. Community resistance and resilience were assessed, as were changes over time in the proportions of species according their water affinity (hydrophytes, amphiphytes and helophytes, documented from the floras), and the effect of dewatering on species renewal and richness.ResultsThe sediment type affected aquatic plant community resistance and resilience, with increasing disturbance intensity for silty, followed by coarse compared with organic sediment. Organic sediment retained water efficiently during dewatering, supporting high community resistance, with the maintenance of amphiphytes and more tolerant hydrophytes. On silty sediment, disturbance was sufficiently high to cause the disappearance of hydrophyte vegetative parts, but propagules rapidly sprouted after rewetting, suggesting their preservation in the sediment and enabling good community resilience. On coarse sediment, a decrease in resident amphiphyte abundance, together with helophyte colonization and maintenance after rewetting were observed. Coarse sediment is not favourable to propagule survival, explaining the low community resilience. Contrary to our hypothesis, a linear positive relationship between disturbance intensity and species richness was observed after dewatering.ConclusionThe present study demonstrates that a simple description of sediment type allows prediction of dewatering impact on aquatic plant communities: organic, silt and coarse sediments were ranked along a gradient of water deficit, along which resistance and resilience decreased.

Mountain passes are higher not only in the tropics

A recent article in Ecography by Zuloaga and Kerr (2016) addressed a prediction of Janzen's (1967) classic contention that mountain passes are higher in the tropics: species assemblages separated by steep thermal gradients are less similar than assemblages separated by small thermal gradients. Their results have some surprising and important additional implications. In the New World, mountain passes are in fact higher in both the tropics and near 55°N. This fact allows a strong test of Simpson's (1964) hypothesis that thermal barriers promote allopatric speciation, which leads to higher species richness. Combined with the results of Zuloaga and Kerr, the Simpson/Janzen hypothesis predicts a peak of richness in southern Alaskan and northern British Columbia. Published data are clearly inconsistent with this prediction. High thermal barriers to dispersal do not necessarily lead to greater species richness.

Risk assessment for the Mexican freshwater crayfish: the roles of diversity, endemism and conservation status

Abstract The freshwater fauna has been judged to be one of the most threatened biotic components in the world. In many tropical‐temperate freshwater habitats worldwide the largest invertebrates are crayfish, as is the case with the cambarid crayfish in Mexico. With 98% of endemic species, most of them with reduced distribution ranges, the Mexican crayfish have not been analysed to examine how diversity, endemism and threat are distributed. A data set was analysed containing 1419 locality records for the 56 species of crayfish occurring in Mexico arranged in a 251 cell grid. Spatial autocorrelation analyses using Moran's I and G* were conducted; species richness, endemism and threat indices were calculated and mapped. An integrated risk score was derived from the two indices. Spatial autocorrelation analyses revealed a pattern that significantly departs from a random arrangement. Moran's I showed a positive autocorrelation between cells that are less than 800 km apart; while G* analysis identified one hotspot of diversity. Four areas with high endemism and seven areas with intermediate endemism values were recognized. The western portion of the Trans‐Mexican Volcanic Belt, and some areas in the north are of special concern owing to the presence of threatened microendemic species. The areas where more threatened species occur differ from those with high endemism values. This distinction makes evident that for species with low dispersal capabilities the areas with high endemism are the product of historical and geological events, while the areas with high numbers of threatened species are those where human activities have had a major impact. The integrated risk score, however, resulting from the combination of endemism and threat, peaks along the Trans‐Mexican Volcanic Belt and where it joins the Sierra Madre Oriental. The integrated risk score proposed in this study, based on well known and frequently used indices in conservation biology, can be used with existing data to determine areas where crayfish species richness, endemism and threat peak to make conservation efforts more cost‐effective. © 2016 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley & Sons, Ltd.

Latitudinal trends in genus richness of vascular plants in the Eocene and Oligocene of North America

The latitudinal richness gradient is a frequent topic of study on the modern landscape, but its history in deep time is much less well known. Here, we preliminarily evaluated the paleolatitudinal richness gradient of vascular plants for the Eocene (56-33.9 million years ago) and Oligocene (33.9-23 million years ago) epochs of North America north of Mexico using 201 fossil floras. We calculated the direction and shape of the gradient using quadratic regression to detect linear and curvilinear trends. We performed regressions for the Eocene and Oligocene as well as for informal time intervals within the Eocene: early, middle, and middle + late. We found that quadratic models better explain the data than linear models for both epochs as well as for the early Eocene. A roughly linear trend in the middle and middle + late intervals may reflect limited sampling of high latitude floras for those times. The curvilinear relationship was weak for the Eocene and the model showed a peak in richness at 45.5°N. The curvilinear relationship was much stronger for the Oligocene and the peak occurred at 48.5°N. In the Eocene, the mid-latitude peak in richness may be explained by mean annual temperature, which was probably higher at some mid-latitudes than at lower ones. For the Oligocene, the peak in richness at mid-latitudes may be explained by evolutionary diversification within the temperate zone or by increased aridity at low latitudes. We also assessed the latitudinal richness gradient of genera within modern floras in North America north of Mexico and we found a weak, curvilinear trend with a peak in richness at 31.5°N. Our results suggest that the latitudinal genus richness gradient of vascular plants in North America continued to develop into its modern structure following the Oligocene.

Rarefaction and elevational richness pattern: a case study in a high tropical island (New Caledonia, SW Pacific)

Aims. To analyse the elevational richness pattern of tree species in New Caledonian tropical rain forests and investigate how the richness pattern is affected by standardizing on area vs standardizing on number of individuals and by sample coverage. Location. New Caledonia (SW Pacific). Methods. We re-analysed data from the New Caledonian Plant Inventory and Permanent Plot Network (NC-PIPPN). In this plot network, all trees (DBH ≥ 5 cm) were inventoried from 201 plots measuring 20 × 20 m and located between 5 and 1292 m a.s.l. We tested whether the number of trees inventoried in these plots affected the elevational richness pattern, and if so, whether plots with large trees have a low species density because of a low number of inventoried trees. This was done by applying individual-based and coverage-based rarefaction procedures with different cut-off threshold values and re-testing the relationship between estimated species richness and elevation. Results About 40% of the variability in species density is explained by variation in the density of trees, which in turn had no obvious pattern with elevation. Plots with large trees (high quadratic mean DBH) contained fewer individuals and thus fewer species. Applying rarefaction changed the observed elevational pattern from a peak in species richness approximately in the middle of the studied elevational gradient to a peak at lower elevations. Both the choice of the rarefaction procedure and the cut-off threshold value used to estimate species richness may dramatically change the elevational pattern. Conclusions. When the local species pool is large, the use of small plots relative to tree size induces a high correlation between species richness and the number of trees inventoried per plot. To analyse appropriately an elevational pattern for such small plot sizes, species richness should be rarefied to provide additional perspectives. We show that rarefaction changes the elevation at which species richness is expected to be maximal and that increasing the cut-off threshold value sharpens the observed humped pattern.

Ancient origin of high taxonomic richness among insects.

Insects are a hyper-diverse group, comprising nearly three-quarters of all named animal species on the Earth, but the environmental drivers of their richness and the roles of ecological interactions and evolutionary innovations remain unclear. Previous studies have argued that family-level insect richness increased continuously over the evolutionary history of the group, but inclusion of extant family records artificially inflated the relative richness of younger time intervals. Here we apply sampling-standardization methods to a species-level database of fossil insect occurrences, removing biases present in previous richness curves. We show that insect family-richness peaked 125 Ma and that Recent values are only 1.5-3 times as high as the Late Palaeozoic. Rarefied species-richness data also tentatively suggest little or no net increase in richness over the past 125 Myr. The Cretaceous peak in family richness was coincident with major radiations within extant groups but occurred prior to extinctions within more basal groups. Those extinctions may in part be linked to mid-Cretaceous floral turnover following the evolution of flowering plants. Negligible net richness change over the past 125 Myr implies that major radiations within extant groups were offset by reduced richness within groups that are now relict or extinct.