Terrestrial Species Richness Research Articles

Reptiles in danger: Implications of road mortality in wetlands of South America

Abstract Undoubtedly, roads produce negative effects on wildlife, but when they are laid across wetlands effects can be exacerbated. The “hyperfragmentation” and loss of terrestrial and aquatic habitats generated by roads makes it urgent to measure effect on wildlife. Reptiles are highly susceptible to road mortality mainly because of their slow movement, and the use of roads as a substrate for thermoregulation and feeding areas. Here, we analysed reptile road mortality in the floodplain of the Paraná River (Argentina) at three sections: North (NS), Centre (CS), and South (SS). We compared the richness and abundance of reptile roadkill species that use different habitats by means of monthly samplings. We found 464 roadkills encompassing 27 species (1 turtle, 2 lizards, and 24 snakes). Despite a greater richness of terrestrial species, roadkill abundance was always dominated by aquatic species. We detected two hot spots of reptile roadkill where routes cross the Paraná River floodplain and the environment quality was high: one in the NS, located in a protected area with records of two Vulnerable species; and another hot spot in the SS, which recorded roadkills that belonged to almost all inhabiting snake species and presented the highest roadkill abundance. A temporal ‘hot moment’ of reptile roadkill occurrence was detected during autumn in the SS. This study provides a baseline for delineating measures to prevent and mitigate reptile mortality, focusing on specific places, moments, and taxa in roads crossing wetlands in the Paraná River floodplain.

Leveraging species richness and ecological condition indices to guide systematic conservation planning

The global crises of biodiversity loss and climate change are interconnected in root cause and solutions. Targeted land conservation has emerged as a leading strategy to protect vulnerable species and buffer climate impacts, however, consistent methods to assess biodiversity and prioritize areas for protection have not yet been established. Recent landscape-scale planning initiatives in California present an opportunity to conserve biodiversity, but to enhance their effectiveness, assessment approaches should move beyond commonly used measures of terrestrial species richness. In this study, we compile publicly available datasets and explore how distinct biodiversity conservation indices - including indicators of terrestrial and aquatic species richness and of biotic and physical ecosystem condition - are represented in watersheds of the northern Sierra Nevada mountain region of California (n = 253). We also evaluate the extent to which the existing protected area network covers watersheds that support high species richness and intact ecosystems. Terrestrial and aquatic species richness showed unique spatial patterns (Spearman R = 0.27), with highest richness of aquatic species in the low-elevation watersheds of the study area and highest richness of terrestrial species in mid- and high-elevation watersheds. Watersheds with the highest ecosystem condition were concentrated in upper-elevations and were poorly correlated with those with the highest species richness (Spearman R = −0.34). We found that 28% of watersheds in the study area are conserved by the existing protected area network. Protected watersheds had higher ecosystem condition (mean rank-normalized score = 0.71) than unprotected areas (0.42), but species richness was generally lower (0.33 in protected versus 0.57 in unprotected watersheds). We illustrate how the complementary measures of species richness and ecosystem condition can be used to guide strategies for landscape-scale ecosystem management, including prioritization of watersheds for targeted protection, restoration, monitoring, and multi-benefit management. Though designed for California, application of these indices to guide conservation planning, design monitoring networks, and implement landscape-scale management interventions provides a model for other regions of the world.

Winter conditions structure extratropical patterns of species richness of amphibians, birds and mammals globally

AbstractAimThe aim was to derive global indices of winter conditions and examine their relationships with species richness patterns outside of the tropics.LocationAll extratropical areas (>25° N and 25° S latitudes), excluding islands.Time period2000–2018.Major taxa studiedAmphibians, birds and mammals.MethodsWe mapped three global indices of winter conditions [number of days of frozen ground (length of frozen ground winter); snow cover variability; and lack of subnivium (below‐snow refuge)] from satellite data, then used generalized additive models to examine their relationships with species richness patterns derived from range data.ResultsLength of frozen ground winter was the strongest predictor of species richness, with a consistent cross‐taxonomic decline in species richness occurring beyond 3 months of winter. It also often outperformed other environmental predictors of species richness patterns commonly used in biodiversity studies, including climate variables, primary productivity and elevation. In areas with ≥3 months of winter conditions, all three winter indices explained much of the deviance in amphibian, mammal and resident bird species richness. Mammals exhibited a stronger relationship with snow cover variability and lack of subnivium than the other taxa. Species richness of fully migratory species of birds peaked at c. 5.5 months of winter, coinciding with low species richness of residents.Main conclusionsOur study demonstrates that winter structures latitudinal and elevational gradients of extratropical terrestrial species richness. In a rapidly warming world, tracking the seasonal dynamics of frozen ground and snow cover will be essential for predicting the consequences of climate change on species, communities and ecosystems. The indices of winter conditions we developed from satellite imagery provide an effective means of monitoring these dynamics into the future.

Considering habitat conversion and fragmentation in characterisation factors for land-use impacts on vertebrate species richness

Human land use is one of the primary threats to terrestrial species richness and is considered a priority for meeting global sustainability and biodiversity targets. Decision-support tools, such as life cycle assessment (LCA), are widely used for developing strategies to achieve such objectives. Currently available life cycle impact assessment (LCIA) methods apply the countryside species-area relationship (c-SAR) to quantify habitat conversion impacts on species richness. However, additional effects of habitat fragmentation are yet ignored in these assessments. We use the species-habitat relationship (SHR), an adaptation of the c-SAR that considers both habitat conversion and fragmentation effects, to develop a new set of land-use characterisation factors for 702 terrestrial ecoregions (in 238 countries), four land-use types (urban, cropland, pasture, and forestry), and four taxonomic groups (amphibians, birds, mammals, and reptiles; plus the aggregate of these vertebrate groups). The SHR generally predicts higher per-area impacts of land-use than the impacts estimated by the c-SAR (a median relative difference of +9%), indicating that land-use impacts may be systematically underestimated when ignoring fragmentation effects. Whereas per-area impacts of land-use on regional species richness are highest in temperate regions, reflecting the diminished extent of natural habitat, per-area impacts of land-use on global species richness are highest in the subtropics, reflecting the importance of tropical regions and islands to global vertebrate species diversity. The large variety in magnitude of land-use impacts across the world's regions emphasizes the importance of regionalised assessments. The set of characterisation factors proposed here can be readily used in environmental decision-making.

Rapid recolonisation of feral cats following intensive culling in a semi-isolated context

Invasive feral cats threaten biodiversity at a global scale. Mitigating feral cat impacts and reducing their populations has therefore become a global conservation priority, especially on islands housing high endemic biodiversity. The New Caledonian archipelago is a biodiversity hotspot showing outstanding terrestrial species richness and endemism. Feral cats prey upon at least 44 of its native vertebrate species, 20 of which are IUCN Red-listed threatened species. To test the feasibility and efficiency of culling, intensive culling was conducted in a peninsula of New Caledonia (25.6 km²) identified as a priority site for feral cat management. Live-trapping over 38 days on a 10.6 km² area extirpated 36 adult cats, an estimated 44% of the population. However, three months after culling, all indicators derived from camera-trapping (e.g., abundance, minimum number of individuals and densities) suggest a return to pre-culling levels. Compensatory immigration appears to explain this unexpectedly rapid population recovery in a semi-isolated context. Since culling success does not guarantee a long-term effect, complementary methods like fencing and innovative automated traps need to be used, in accordance with predation thresholds identified through modelling, to preserve island biodiversity. Testing general assumptions on cat management, this article contributes important insights into a challenging conservation issue for islands and biodiversity hotspots worldwide.

A global assessment of the drivers of threatened terrestrial species richness

High numbers of threatened species might be expected to occur where overall species richness is also high; however, this explains only a proportion of the global variation in threatened species richness. Understanding why many areas have more or fewer threatened species than would be expected given their species richness, and whether that is consistent across taxa, is essential for identifying global conservation priorities. Here, we show that, after controlling for species richness, environmental factors, such as temperature and insularity, are typically more important than human impacts for explaining spatial variation in global threatened species richness. Human impacts, nevertheless, have an important role, with relationships varying between vertebrate groups and zoogeographic regions. Understanding this variation provides a framework for establishing global conservation priorities, identifying those regions where species are inherently more vulnerable to the effects of threatening human processes, and forecasting how threatened species might be distributed in a changing world.

Contribution of rare and common species to subterranean species richness patterns.

AimCommon species contribute more to species richness patterns (SRPs) than rare species in most studies. Our aim was to test this hypothesis using a novel model system, species living exclusively in subterranean habitats. They consist of mainly rare species (small ranges), only a few of them being common (large ranges), and challenge whether rare species are less important for the development of SRPs in this environment. We separately analyzed aquatic and terrestrial species.LocationWestern Balkans in southeastern Europe.MethodsWe assembled two datasets comprising 431 beetle and 145 amphipod species, representing the model groups of subterranean terrestrial and aquatic diversity, respectively. We assessed the importance of rare and common species using the stepwise reconstruction of SRPs and subsequent correlation analyses, corrected also for the cumulative information content of the subsets based on species prevalence. We applied generalized linear regression models to evaluate the importance of rare and common species in forming SRPs. Additionally, we analyzed the contribution of rare and common species in species‐rich cells.ResultsPatterns of subterranean aquatic and terrestrial species richness overlapped only weakly, with aquatic species having larger ranges than terrestrial ones. Our analyses supported higher importance of common species for forming overall SRPs in both beetles and amphipods. However, in stepwise analysis corrected for information content, results were ambiguous. Common species presented a higher proportion of species than rare species in species‐rich cells.Main ConclusionWe have shown that even in habitats with the domination of rare species, it is still common species that drive SRPs. This may be due to an even spatial distribution of rare species or spatial mismatch in hotspots of rare and common species. SRPs of aquatic and terrestrial subterranean organisms overlap very little, so the conservation approaches need to be habitat specific.

Vascular plant species richness and bioindication predict multi‐taxon species richness

Abstract Plants regulate soils and microclimate, provide substrate for heterotrophic taxa, are easy to observe and identify and have a stable taxonomy, which strongly justifies their use as indicators in monitoring and conservation. However, there is no consensus as to whether plants are strong predictors of total multi‐taxon species richness. In this study, we investigate if general terrestrial species richness can be predicted by vascular plant richness and bioindication. To answer this question, we collected an extensive dataset on species richness of vascular plants, bryophytes, macrofungi, lichens, plant‐galling arthropods, gastropods, spiders, carabid beetles, hoverflies, and genetic richness (operational taxonomic units = OTUs) from environmental DNA metabarcoding. We also constructed a Conservation Index based on threatened red list species. Besides using richness of vascular plants for prediction of other taxonomic groups, we also used plant‐derived calibration of the abiotic environment (moisture, soil fertility and light conditions) as well as the degree of anthropogenic impact. Bivariate relationships between plant species richness and other species groups showed no consistent pattern. After taking environmental calibration by bioindication into account, we found a consistent, and for most groups significant, positive effect of plant richness. Plant species richness was also important for richness of fungal OTUs, Malaise OTUs and for the Conservation Index. Our multiple regression analyses revealed (a) a consistently positive effect of plant richness on other taxa, (b) prediction of 12%–55% of variation in other taxa and 48% of variation in the total species richness when bioindication and plant richness were used as predictors. Our results justify that vascular plants are strong indicators of total biodiversity across environmental gradients and broad taxonomic realms and therefore a natural first choice for biodiversity monitoring and conservation planning.

Nuevos datos del uso de la costa en el extremo sur del continente por cazadores-recolectores durante el Holoceno tardío. El sitio Cabo Vírgenes 24 (Santa Cruz, Argentina)

El sitio Cabo Vírgenes 24 (CV24) se ubica en el extremo sureste de la Patagonia continental y presenta ocupaciones entre 753-888 (1270 ± 60 14C A.P - LP3229) y 545-626 años Cal A.P (619 ± 26 14C A.P - AA106800). Los artefactos líticos se confeccionaron con materias primas disponibles localmente (dacita y RGFO). El componente expeditivo de la tecnología concuerda con la de cazadores de guanacos del interior del continente. Se observa una baja densidad y riqueza moderada de especies marinas y terrestres con un énfasis en la explotación de pinnípedos (Arctocephalus australis y Otaria flavescens), seguida de guanacos (Lama guanicoe) y un menor uso de aves marinas (Phalacrocorax sp., Spheniscus magellanicus y Aptenodytes patagonicus). La información provista por CV24 reafirma las tendencias observadas respecto de la utilización esporádica y marginal de la localidad de Cabo Vírgenes por parte de cazadoresrecolectores desde el Holoceno tardío hasta el contacto con los europeos.

Effect of the Long-Term Mean and the Temporal Stability of Water-Energy Dynamics on China’s Terrestrial Species Richness

Water-energy dynamics broadly regulate species richness gradients but are being altered by climate change and anthropogenic activities; however, the current methods used to quantify this phenomenon overlook the non-linear dynamics of climatic time-series data. To analyze the gradient of species richness in China using water-energy dynamics, this study used linear regression to examine how species richness is related to (1) the long-term mean of evapotranspiration (ET) and potential evapotranspiration (PET) and (2) the temporal stability of ET and PET. ET and PET were used to represent the water-energy dynamics of the terrestrial area. Changes in water-energy dynamics over the 14-year period (2000 to 2013) were also analyzed. The long-term mean of ET was strong and positively ( R 2 ∈ ( 0.40 ~ 0.67 ) , p < 0.05 ) correlated with the species richness gradients. Regions in which changes in land cover have occurred over the 14-year period (2000 to 2013) were detected from long-term trends. The high level of species richness in all groups (birds, mammals, and amphibians) was associated with relatively high ET, determinism (i.e., predictability), and entropy (i.e., complexity). ET, rather than PET or temporal stability measures, was an effective proxy of species richness in regions of China that had moderate energy (PET > 1000 mm/year), especially for amphibians. In addition, predictions of species richness were improved by incorporating information on the temporal stability of ET with long-term means. Amphibians are more sensitive to the long-term ET mean than other groups due to their unique physiological requirements and evolutionary processes. Our results confirmed that ET and PET were strongly and significantly correlated with climatic and anthropogenic induced changes, providing useful information for conservation planning. Therefore, climate management based on changes to water-energy dynamics via land management practices, including reforestation, should be considered when planning methods to conserve natural resources to protect biodiversity.

Quantifying the effects of the break up of Pangaea on global terrestrial diversification with neutral theory.

The historic richness of most taxonomic groups increases substantially over geological time. Explanations for this fall broadly into two categories: bias in the fossil record and elevated net rates of diversification in recent periods. For example, the break up of Pangaea and isolation between continents might have increased net diversification rates. In this study, we investigate the effect on terrestrial diversification rates of the increased isolation between land masses brought about by continental drift. We use ecological neutral theory as a means to study geologically complex scenarios tractably. Our models show the effects of simulated geological events that affect all species equally, without the added complexity of further ecological processes. We find that continental drift leads to an increase in diversity only where isolation between continents leads to additional speciation through vicariance, and where higher taxa with very low global diversity are considered. We conclude that continental drift by itself is not sufficient to account for the increase in terrestrial species richness observed in the fossil record.

A camera trap assessment of terrestrial mammals in Machalilla National Park, western Ecuador

Understanding the abundance, geographicdistribution, and conservation status of terrestrial mam­mals is vital to promote effective wildlife management in protected areas. Located in the Tumbes-Chocó-Magdalena hotspot of western Ecuador, Machalilla National Park contains high levels of biodiversity and endemism but suffers from habitat loss and degradation. This study provides an updated inventory of medium-sized to large mammals in the park and assesses changes in species richness over the past 20 years. Surveying 70% of Machalilla’s 562-km2 terrestrial area with 60 camera trap points, we detected 18 species of mammals belonging to 13 families. Richness of terrestrial species has declined in recent decades, due to the disappearance of keystone species like Jaguar (Panthera onca), White-lipped Peccary (Tayassu pecari), and possibly the Sechuran Fox (Lycalopex sechurae). We recommend specific man­agement improvements to ensure conservation of the unique ecosystems and biodiversity of Machalilla, the only national park in Ecuador containing dry forest.

Incipient radiation within the dominant Hawaiian tree Metrosideros polymorpha.

Although trees comprise a primary component of terrestrial species richness, the drivers and temporal scale of divergence in trees remain poorly understood. We examined the landscape-dominant tree, Metrosideros polymorpha, for variation at nine microsatellite loci across 23 populations on young Hawai'i Island, sampling each of the island's five varieties throughout its full geographic range. For four varieties, principal coordinate analysis revealed strong clustering of populations by variety across the 10 430 km(2) island, indicating partitioning of the species into multiple evolutionarily significant units. The single island-endemic form, riparian var. newellii, showed especially strong differentiation from other varieties despite occurring in sympatry with other varieties and likely evolved from a bog form on the oldest volcano, Kohala, within the past 500 000 years. Along with comparable riparian forms on other Pacific Islands, var. newellii appears to represent parallel incipient ecological speciation within Metrosideros. Greater genetic distance among the more common varieties on the oldest volcano and an inverse relationship between allelic diversity and substrate age appear consistent with colonization of Hawai'i Island by older, partially diverged varieties followed by increased hybridization among varieties on younger volcanoes. This study demonstrates that broad population-level sampling is required to uncover patterns of diversification within a ubiquitous and long-lived tree species. Hawaiian Metrosideros appears to be a case of incipient radiation in trees and thus should be useful for studies of divergence and the evolution of reproductive isolating barriers at the early stages of speciation.

Terrestrial and aquatic flora along a mesotrophic lake shore remaining under increasing human impact: a case study of Lake Powidzkie (Poland)

Terrestrial and aquatic flora along a mesotrophic lake shore remaining under increasing human impact: a case study of Lake Powidzkie (Poland) Floristical investigations were carried out in 2009 in both terrestrial and littoral zones along the NW shore of the mesotrophic Lake Powidzkie (a Natura 2000 site: PLH300026). The results comprise: a general comparison of aquatic vs. terrestrial species richness; a census of 296 species of vascular plants and 7 species of charophytes; the taxonomical, biological (life forms) and geographical-historical (native vs. alien taxa) structure of vascular flora. Distribution of nationally and regionally threatened and legally protected species is presented on maps which illustrate that most of these taxa are concentrated in Lake Powidzkie and in its neighbourhood. The ongoing synanthropization of the flora is assessed and discussed considering localities of chosen alien species and their occurrence within natural plant communities: 21 of 27 aliens were recorded at least once in natural vegetation, whereas 4 of them (Aster lanceolatus, Elodea canadensis, Impatiens parviflora and Rhus typhina) formed their own, xenospontaneous communities. The main conclusion is that while the area still abounds in regionally valuable components of native biodiversity, it simultaneously is more and more threatened by increasing anthropopressure, which has already been manifested by the presence of many potentially invasive alien species.

Evolution in action across life at “Evolution Canyons”, Israel

The Evolution Canyon model reveals evolution in action across life at a microscale involving biodiversity divergence, adaptation and incipient sympatric ecological speciation across life. The model highlights diverse taxa species richness, genomics, proteomics and phenomics phenomena by exploring genetic polymorphisms at protein and DNA levels and, recently, genome-wide gene expression and regulation. Genetic diversity and divergence reveal evolutionary dynamics of natural populations exposed to sharp-interslope, ecologically divergent, tropical and temperate microclimates on a xeric, tropical, African south-facing slope (AS) abutting with a mesic, temperate, European north-facing slope (ES) separated by 200 meters on average. Four Evolution Canyons” (EC) are currently being investigated in Israel in the Carmel, Galilee, Negev, and Golan Mountains (EC I-IV), respectively. We identified 2,500 species in ECI (Carmel) from bacteria to mammals in an area of 7,000 m2. Local biodiversity patterns parallel global patterns. Higher terrestrial species richness was found on the AS. Aquatic species richness prevails on the ES. In 9 out of 14 (64%) model organisms across life, we identified a significantly higher genetic polymorphism on the more stressful AS. Likewise, in some model taxa, we found largely higher levels of mutation rates, gene conversion, recombination, DNA repair, genome size, small sequence repeats (SSRs), single nucleotide polymorphism (SNPs), retrotransposons, transposons, candidate gene diversity, and genome-wide gene expression and regulation on the more stressful AS. Remarkably, interslope incipient sympatric ecological speciation was found across life from bacteria to mammals. The Evolution Canyon model represents the Israeli ecological analogue of the Galapagos Islands. Micro- climatic selection overrides gene flow and drift, and drives both interslope adaptive divergence and incipient sympatric ecological speciation at a microscale. The EC model could potentially highlight many mysteries of evolutionary biology including the genetic basis of adaptation and speciation, especially now with the rapid high-throughput techniques of whole genome analysis.

Testing the impact of climate variability on European plant diversity: 320 000 years of water–energy dynamics and its long‐term influence on plant taxonomic richness

Models examining the present-day relationship between macro-scale patterns in terrestrial species richness and variables of water and energy demonstrate that a combined water-energy model is a good predictor of richness in mid-to-high latitude regions. However, the power of the individual water and energy variables to explain this richness through time has never been explored. Here, we assess how well energy and water can predict long-term variations in plant richness using a 320,000-year fossil pollen data set from Hungary. Results demonstrate that a combined water-energy model best explains the variation in plant diversity through time. However, this long temporal record also demonstrates that amplitude of energy variation appears to be a strong determinant of richness. Decreased richness correlates with increased climate variability and certain species appear to be more susceptible according to their ecological traits. These findings have important implications for predicting richness at times of increasing climate variability.

"Evolution Canyon": A Microcosm of Life's Evolution Focusing on Adaptation and Speciation

Local microcosmic natural laboratories, dubbed "Evolution Canyon" (EC) models, reinforce studies of regional and global macrocosmic ecological theaters across life and unravelevolution in action.The EC model laboratories permit genomic, proteomic, and phenomic studies highlighting speciation and adaptation at a microscale. Critical transplant experiment tests can evaluate interslope differential fitness. Novel techniques of genetic mapping, sequence nucleotide polymorphisms (SNPs), and wide genome coding and noncoding expressions can unravel evolutionary dynamics. Finally, fundamental problems such as stress effects on nonrandom mutations, lateral transfers, splicing variations, sex, and social evolutions, and adaptive strategies of prokaryotes and eukaryotes are testable. We are studying four "Evolution Canyons" (EC I-IV) in the Carmel, Galilee, Negev, and Golan mountains. We've identified 2,500 species in EC I (Carmel) from bacteria to mammals in an area of 7,000 m. Higher terrestrial species richness was found on the more stressful tropical "African" slope (AS). Aquatic species richness was higher on the milder, temperate "European" slope (ES). In soil fungi we found interslope local and regional adaptive divergence in sex, melanism, and conidia. In nine out of 14 (64%) model organisms across life we identified largely higher genetic polymorphisms on the more stressful "African" slope. In some model species we found higher mutation rates, gene conversion, recombination, DNA repair, and larger genome size as well as interslope divergent micro-satellites, molecular polymorphisms, retrotransposons, and wide-genome gene expression on the more stressful AS. Remarkably, interslope incipient sympatric speciation was found across life. The "Evolution Canyon" model represents the Israeli ecological equivalent of the Galapagos Islands. Micro-climatic selection overrides drift and drives both interslope adaptive radiation and incipient sympatric speciation. The EC model could potentially highlight many mysteries of evolutionary biology.

Variation in plant species richness in and adjacent to 64 ponds in SE Norwegian agricultural landscapes

All vascular plants, classified by life and growth form into six groups, four groups of hydrophytes (lemnids, nymphaeids, elodeids and isoetids), helophytes, and terrestrial species of pond margins, were inventoried in 64 SE Norwegian agricultural landscape ponds and their adjacent margins. The study sites varied considerably with respect to species richness; 0–4 for each hydrophyte group, 0–9 for helophytes, and 13–77 for terrestrial species. A total of 56 explanatory variables were recorded for each pond and adjacent margin to explain the observed richness variability. Species richness in each plant group was modelled separately by generalised linear models (GLM), using the recorded explanatory variables as predictors. Pond area, water depth and water chemical variables were the most important predictors of hydrophyte and helophyte species richness, followed by fluctuation and human impact variables such as liming and presence of ducks and fish. Pond margin area and geographical variables were significant predictors of richness of terrestrial species of pond margins. The contribution of different structuring processes to explanation of species richness patterns is discussed. The generally weak explanatory power of the selected variables indicates high importance of apparent randomness in this ecosystem, and, notably, that the ponds and their adjacent margins represent islands in the agricultural landscape that accumulate species more or less individualistically.

Species richness and distribution of ferns along an elevational gradient in Costa Rica

To better understand changes in the distribution and diversity within plant functional types along an elevational gradient and the potential mechanisms driving such changes, we studied species richness of ferns at six elevations along a forested elevational gradient in Costa Rica, from La Selva Biological Station at 30 m a.s.l. up the slopes of Volcán Barva to 2960 m a.s.l. Among the samples from all the sites combined, we found 264 species from 60 genera. Sixty‐nine species were terrestrial, 113 were canopy epiphytes, and 121 were low‐trunk epiphytes. Only one species occupied both canopy and terrestrial habitats at any of the study sites. Overlap of canopy and low‐trunk species composition was relatively low (18%), and lower still was the overlap of terrestrial and low‐trunk species (12%). Total species richness peaked at the 1000‐m site for canopy and low‐trunk epiphytic species. In contrast, the richness of terrestrial species rose to a mid‐elevation maximum and remained relatively constant at higher elevations. In an effort to explain elevational patterns of species richness, we examined mean annual rainfall and temperature, light intensities in the canopy and at ground level, and the mid‐domain effect. Of the explanatory factors examined, the mid‐domain effect accounted for most of the elevational pattern. We found little evidence that environmental gradients drive patterns of fern species richness on this spatial scale.

Weak links: ‘Rapoport's rule’ and large‐scale species richness patterns

SummaryMany hypotheses have been proposed to explain regional species richness patterns. Among these, ‘Rapoport's rule’ has sparked considerable controversy by stating that the latitudinal gradient in species richness can be explained indirectly as a function of narrower geographic ranges for species at low latitudes. Annual climatic variability, or deviation from mean climatic conditions, has been hypothesized to moderate this phenomenon. Furthermore, taxa that avoid much of this seasonality, such as temperate zone insects that enter diapause or species that migrate, were predicted to show reduced latitudinal gradients in richness. I test the suggested link between ‘Rapoport's rule’ and species richness for two higher level insect taxa as well as for the class Mammalia. Although these taxa exhibit the well‐known latitudinal gradient in species richness, simple annual climatic variability and deviation from mean annual climatic conditions provide very poor predictions of species richness in each of them. Potential evapotranspiration, a measurement of ambient climatic energy, explains most of the observed variance in regional species richness patterns for all three taxa, consistent with the species richness‐energy hypothesis. I find no support for an indirect link between ‘Rapoport's rule’ and terrestrial species richness patterns in North America.