Ant Diversity and Abundance along an Elevational Gradient in the Philippines1

Ant communities were surveyed along an elevational gradient in the Philippines extending from lowland dipterocarp forest (250 m elevation) to mossy forest (1750 m). Standardized pitfall trapping in arboreal and terrestrial microhabitats at seven sites yielded 51 species. Collecting by hand at five of the sites yielded 48 species. The two methods produced substantially different assemblages, with only 22 species (29%) taken in common. Only a fraction of the total ant community appeared to be sampled at most of the sites. Measures of species richness and relative abundance peaked at mid-elevations and declined sharply with increasing elevation. Ants were extremely rare above 1500 m elevation. Arboreal ants were trapped much less frequently than terrestrial ants at all sites. Ant species that were abundant had broader elevational distributions than those that were less common, but most species were rare and occurred at only one or two sites. The elevational patterns for ants are largely the inverse of those documented for Philippine small mammals which reach their greatest diversity and abundance at high elevations where ants are rare. This suggests that the two groups may interact competitively. Some of the patterns observed or inferred from this study may apply to tropical ant communities in general, and are presented as series of testable hypotheses as a guide and stimulus for future research.     

Elevation gradients of diversity for rodents and bats in Oaxaca, Mexico

1  This study documents patterns of rodent and bat diversity related to abiotic and biotic factors along elevational gradients in the Sierra Mazateca (640–2600 m a.s.l.) and Sierra Mixteca (700–3000 m a.s.l.) in Oaxaca, Mexico.
2  The two transects share similar faunas: 17 and 23 rodent species were captured in the sierras Mazateca and Mixteca, respectively, 14 of which occurred on both transects. Rodent species richness was similar in the wet season and the dry season along both transects. Rodent species richness peaked at 1025–1050 m in tropical semi-deciduous forest on both transects. Endemic species were restricted to high-elevation habitats.
3  Sixteen and 17 bat species were captured in the sierras Mazateca and Mixteca, respectively; 11 occurred on both transects. Bat species richness was higher in the wet season than in the dry season in the Sierra Mazateca. Bat species richness peaked at 1850 m in pine–oak forest in the Sierra Mazateca, and at 750 m and 1050 m in tropical semi-deciduous forest in the Sierra Mixteca, decreasing abruptly at higher elevations on both transects.
4  Patterns of trophic diversity of rodents and bats coincided with those of species richness on each transect. Species richness increased with increasing habitat diversity; increased with increasing rainfall and productivity; increased with increasing resource diversity; and increased in areas with high rates of speciation (rodents only).
5  The need for conservation action in Oaxaca is urgent and proponents should promote establishment of protected areas linking lowland habitats with high species richness to high-elevation habitats harbouring large numbers of endemic forms.     

Small mammal species richness and turnover along elevational gradient in Yulong Mountain,Yunnan, Southwest China

Understanding the species diversity patterns along elevational gradients is critical for biodiversity conservation in mountainous regions. We examined the elevational patterns of species richness and turnover, and evaluated the effects of spatial and environmental factors on nonvolant small mammals (hereafter “small mammal”) predicted a priori by alternative hypotheses (mid‐domain effect [MDE], species–area relationship [SAR], energy, environmental stability, and habitat complexity]) proposed to explain the variation of diversity. We designed a standardized sampling scheme to trap small mammals at ten elevational bands across the entire elevational gradient on Yulong Mountain, southwest China. A total of 1,808 small mammals representing 23 species were trapped. We observed the hump‐shaped distribution pattern of the overall species richness along elevational gradient. Insectivores, rodents, large‐ranged species, and endemic species richness showed the general hump‐shaped pattern but peaked at different elevations, whereas the small‐ranged species and endemic species favored the decreasing richness pattern. The MDE and the energy hypothesis were supported, whereas little support was found for the SAR, the environmental stability hypothesis, and the habitat complexity. However, the primary driver(s) for richness patterns differed among the partitioning groups, with NDVI (the normalized difference vegetation index) and MDE being the most important variables for the total richness pattern. Species turnover for all small mammal groups increased with elevation, and it supported a decrease in community similarity with elevational distance. Our results emphasized for increased conservation efforts in the higher elevation regions of the Yulong Mountain.     

Elevational diversity gradients, biogeography and the structure of montane mammal communities in the intermountain region of North America

1  Distribution data were assembled for non-volant small mammals along elevational gradients on mountain ranges in the western U.S.A. Elevational distributions in the species-rich Uinta Mountains were compared to those on smaller mountain ranges with varying degrees of historical isolation from the Uintas.
2  For mountain ranges supporting the richest faunas, species richness is highest over a broad low- to mid-elevation zone and declines at both lower and higher elevations. Patterns on other mountain ranges are similar but reflect lower overall species richness.
3  A basic relationship between elevational and geographical distribution is apparent in the occurrence patterns of mammals on regional mountains. Faunas on mountains that have had low levels of historical isolation appear to be influenced by immigration rather than extinction. Species restricted to high elevations in the Uintas are poorly represented on historically isolated mountains and form a portion of local faunas shaped by extinction. Species occurring at lower elevations in the Uintas have better representation on isolated mountains and apparently maintain populations through immigration.
4  Several widespread species show substantial variation in maximum elevation records on different mountain ranges. This involves (1) an upward shift in habitat zones on small, isolated mountain ranges, allowing greater access by low-elevation species, and (2) expansion of certain low- and mid-elevation species into habitats normally occupied by absent high-elevation taxa.
5  Results indicate that montane mammal faunas of the intermountain region have been shaped by broad-scale historical processes, unique regional geography and local ecological dynamics. Parallel examples among mammals of the Philippine Islands suggest that such patterns may characterize many insular faunas.     

Elevation gradients of species-density: historical and prospective views

Studies of elevation clines in diversity and composition of ecological communities date back to the origins of biogeography. A modern resurgence of interests in these elevational clines is likely to contribute important insights for developing a more general theory of species diversity. In order to gain a more comprehensive understanding of geographical clines in diversity, the research programme for montane biogeography should include statistically rigorous tests of apparent patterns, comparisons of patterns among regions and taxonomic or ecological groups of species, and analyses of clines in environmental variables concurrent with biogeographical surveys. The conceptual framework for this research programme should be based on the assumption that elevational gradients in species diversity result from a combination of ecological and evolutionary processes, rather than the presumed independent effects of one overriding force. Given that montane ecosystems are hot spots of biological diversity, an expanded and integrated programme for biogeographic surveys in montane regions should provide valuable insights for conservation biologists.     

Bird diversity along elevational gradients in the Andes of Colombia: area and mass effects

Aim The decrease in species richness with increasing elevation is a widely recognized pattern. However, recent work has shown that there is variation in the shape of the curve, such that both negative monotonic or unimodal patterns occur, influenced by a variety of factors at local and regional scales. Discerning the shape of the curve may provide clues to the underlying causes of the observed pattern. At regional scales, the area of the altitudinal belts and mass effects are important determinants of species richness. This paper explores the relationship between bird species richness, elevation, mass effects and area of altitudinal zones for birds in tropical mountains. Location The three Andean ranges of Colombia and the peripheral mountain ranges of La Macarena and Santa Marta. Methods Lists of bird species were compiled for altitudinal belts in eastern and western slopes of the three Andean Cordilleras and for La Macarena and Santa Marta. The area of the altitudinal belts was computed from digital elevation models. The effect of area was analysed by testing for differences among altitudinal belts in the slopes and intercepts of the species‐area relationships. Mass effects were explored by separately analysing two sets of species: broadly distributed species, i.e. lowland species whose distributions extend into the Andes, and tropical Andean species, i.e., species that evolved in the Andes. Results Plotting total number of species in each altitudinal belt revealed a decline in species richness with elevation. In slopes with a complete elevational gradient from lowlands to mountain peaks, the decrease was monotonic. In internal Andean slopes where the lower elevational belts are truncated, there was a peak at mid elevations. There was a linear relationship between number of species and area of the altitudinal belts. When controlling for area, there were no differences in the number of species among altitudinal belts (500–2600 m), except for the two upper‐elevation zones (2600–3200 and > 3200 m), which had lower species richness. Diversity of widely distributed species declined monotonically with elevation, whereas tropical Andean species exhibited a mid‐elevation peak. Main conclusions A large proportion of the variation in species richness with elevation was explained by area of the altitudinal belts. When controlling for area, species richness remained constant up to 2600 m and then decreased. This pattern contrasts with a previously reported hump‐shaped pattern for Andean birds. Diversity patterns of widely distributed species suggested that immigration of lowland species inflates diversity of lower elevational belts through mass effects. This influence was particularly evident in slopes with complete altitudinal gradients (i.e. connected to the lowlands). Tropical Andean species, in contrast, were more diverse in mid‐elevational belts, where speciation rates are expected to be higher. The influence of these species was more prevalent in internal Andean slopes with no connection to the lowlands. The decline of species richness at high elevations may be related to higher extinction rates and lower resource levels.     

Elevational gradients of small mammal diversity on the northern slopes of Mt. Qilian, China

Aim Small mammal species richness and relative abundance vary along elevational gradients, but there are different patterns that exist. This study reports the patterns of distribution and abundance of small mammals along the broader elevational gradient of Mt. Qilian range. Location The study was conducted in the Mt. Qilian range, north‐western China, from June to August 2001. Methods Removal trapping was conducted using a standardized technique at 7 sites ranging between 1600 and 3900 m elevation within three transects. Correlation, regression and graphical analyses were used to evaluate the diversity patterns along this elevational gradient. Results In total, 586 individuals representing 18 nonvolant small mammal species were collected during 20 160 trap nights. Species composition was different among the three transects with 6 (33%) of the species found only within one transect. Elevational distribution and relative abundance of small rodents showed substantial spatial variation, with only 2 species showing nonsignificant capture frequencies across elevations. Despite these variations, some general patterns of elevational distribution emerged: humped‐shape relationships between species diversity and elevation were noted in all three transects with diversity peaks at middle elevations. In addition, relative abundance was negatively correlated with elevation. Conclusions Results indicate that maximum richness and diversity of nonvolant small mammals occurred at mid‐elevations where several types of plants reached their maximum diversity and primary productivity, and where rainfall and humidity reached a maximum. It is demonstrated that the mid‐elevation bulge is a general feature of at least a large portion of the biota on the Mt. Qilian range.     

Patterns of ant species richness along elevational gradients in an arid ecosystem

Aim In this study, we examine patterns of local and regional ant species richness along three elevational gradients in an arid ecosystem. In addition, we test the hypothesis that changes in ant species richness with elevation are related to elevation‐dependent changes in climate and available area. Location Spring Mountains, Nevada, U.S.A. Methods We used pitfall traps placed at each 100‐m elevational band in three canyons in the Spring Mountains. We compiled climate data from 68 nearby weather stations. We used multiple regression analysis to examine the effects of annual precipitation, average July precipitation, and maximum and minimum July temperature on ant species richness at each elevational band. Results We found that patterns of local ant species richness differed among the three gradients we sampled. Ant species richness increased linearly with elevation along two transects and peaked at mid‐elevation along a third transect. This suggests that patterns of species richness based on data from single transects may not generalize to larger spatial scales. Cluster analysis of community similarity revealed a high‐elevation species assemblage largely distinct from that of lower elevations. Major changes in the identity of ant species present along elevational gradients tended to coincide with changes in the dominant vegetation. Regional species richness, defined here as the total number of unique species within an elevational band in all three gradients combined, tended to increase with increasing elevation. Available area decreased with increasing elevation. Area was therefore correlated negatively with ant species richness and did not explain elevational patterns of ant species richness in the Spring Mountains. Mean July maximum and minimum temperature, July precipitation and annual precipitation combined to explain 80% of the variation in ant species richness. Main conclusions Our results suggest that in arid ecosystems, species richness for some taxa may be highest at high elevations, where lower temperatures and higher precipitation may support higher levels of primary production and cause lower levels of physiological stress.     

Elevational diversity patterns of small mammals on Mount Kinabalu, Sabah, Malaysia

1 Diversity patterns of small mammals were studied along an elevational transect on Mount Kinabalu, the highest mountain in South‐east Asia, utilizing data from previously existing sources and a new field study. A mark‐and‐release study (conducted during wet and dry seasons between November 1994 and April 1995) resulted in captures of 12 small mammal species, including two species of squirrels, two tree shrews, seven murid rodents and one gymnure. 2 Based on data compiled from this survey, museum specimens, and published and unpublished literature (analysed by locally weighted sums of squares and quadratic polynomial regressions), species richness of small mammals formed a middle elevation bulge, highest at about 1200–1400 m and declining at lower and higher elevations. Trapping during two seasons did not change the assessment of the pattern. 3 A cluster analysis of these data indicated that there are two elevationally associated faunas, one in the highlands and another in the lowlands. The transition between these two assemblages is at 1700–1800 m elevation. The lowland faunal assemblage has the highest number of species, with maximum species richness at about 1300 m for total small mammal species, about 1200 m for arboreal species and about 1400 m for terrestrial species. 4 The areas where much overlapping of species occurs are the elevations where climate and vegetation change rapidly from lowland to montane types. Tree species, gymnosperms, orchids and ferns showed a similar curvilinear pattern along the same elevational gradient, with maximum species richness at about 1400–1500 m. Temperature declined progressively with increasing elevation, but rainfall and humidity reached their highest levels at about 1700 m. 5 Maximum diversity of small mammals thus occurred at the elevation where a highland and a lowland assemblage overlapped, where several types of plants reached their maximum diversity, and where rainfall and humidity reached their maxima. Similar patterns have been documented for small mammals, plants, and climate at sites scattered in Indo‐Australia from Taiwan to New Guinea.     

The mid-domain effect applied to elevational gradients: species richness of small mammals in Costa Rica

Aim The objective of this study was to comprehensively document and examine the alpha and gamma patterns of species richness in non-volant, small mammals (rodents, shrews and mouse opossums) along a tropical elevational gradient. These data were used to determine the support for existing hypotheses of species richness encompassing mid-domain null models, as well as climatic, and community overlap hypotheses. Location Field studies were conducted along a Caribbean slope of the Río Peñas Blancas watershed in the north-eastern region of Costa Rica between 750 and 1850 m at 10 sampling sites. Methods Species richness and abundances of small mammals were surveyed for four seasons including three temporal replicates at each of five elevational sites: late wet season (2000), early wet season (2001), and dry season (2002), and one spatial replicate at five different sites within the same elevations during the late wet season (2001). Species richness at elevations below 700 m was compiled from specimen records from 23 US national and international collections. Predictions of a null model based solely on geometric constraints were examined using a Monte Carlo simulation program, Mid-Domain Null. Results In 16,900 trap nights, 1561 individuals from 16 species were captured. Both alpha and gamma species richness peaked at mid-elevation between 1000 and 1300 m, with richness declining both at higher and lower elevations. Most of the empirical curves of species richness occur within 95% prediction curves of the mid-domain model, although deviations from the null model exist. Regression of the empirical richness on the null model predictions explained nearly half of the variation observed (r² = 0.45, P = 0.002). Main conclusions The geometric constraints of montane topography appear to influence the diversity pattern of small mammals, although climatic conditions including an intermediate rainfall and temperature regime, and distance from the persistent cloud cap also are correlated with the pattern of species richness. The predictions of productivity, and community overlap hypotheses are not supported with the empirical data.     

Diversity patterns of small mammals in the Zambales Mts., Luzon, Philippines

In 2004 and 2005, we conducted a survey of the small mammals on Mt. Tapulao (=Mt. High Peak, 2037 m) in the Zambales Mountains, Luzon Island, Philippines in order to obtain the first information on the mammals of this newly discovered center of endemism. We also tested two hypotheses regarding the relationship of species richness with elevation and the impact of alien species on native mammals. The survey covered five localities representing habitats from regenerating lowland rain forest at 860 m to mossy rain forest near the peak at 2024 m. We recorded 11 species, including 1 native shrew, 1 alien shrew, 8 native rodents, and 1 alien rodent. Two species of Apomys and one species of Rhynchomys are endemic to Zambales; this establishes the Zambales Mountains as a significant center of mammalian endemism. Species richness of native small mammals increased with elevation, from five species in the lowlands at 925 m to seven species in mossy forest at 2024 m; total relative abundance of native small mammals increased from 925 to 1690 m, then declined at 2024 m. Alien small mammals were restricted to highly disturbed areas. Our results support the prediction that maximum species richness of small mammals would occur in lower mossy forest near the peak, not near the center of the gradient. Our results also support the hypothesis that when a diverse community of native Philippine small mammals is present in either old-growth or disturbed forest habitat, “invasive” alien species are unable to penetrate and maintain significant populations in forest.     

神农架自然保护区非飞行哺乳动物的物种丰富度:沿海拔梯度的分布格局

于1999～2001年调查了神农架自然保护区6个地点不同栖息地的非飞行哺乳动物的物种丰富度。栖息地分为8类：原始林、择伐林（采伐枯立木）、次生林、灌木林、草地、常年性河流水溪、农田和人居住区。小型非飞行哺乳动物调查用捕鼠夹;大型非飞行哺乳动物调查主要根据皮张收购资料以及样线法和痕迹法;用10 m×10 m的样方调查林地树种丰富度。调查发现,神农架自然保护区有非飞行哺乳动物59种［不包括引进种梅花鹿（Cervus nippon）］。在同一海拔高度,原始林通常比择伐林和次生林的物种丰富度高,说明采伐严重降低了物种丰富度。对比同一栖息地不同海拔高度的物种丰富度,我们发现,在中海拔地段（800～1700 m）物种丰富度最高：如在原始林和次生林,海拔1700 m的东溪物种丰富度最高;在择伐林,海拔800 m的九冲物种丰富度最高。聚类分析显示,6个地点的哺乳动物物种组成可以分为两组：高海拔组（2100 m以上）和中低海拔组（1700 m以下）。各地点的哺乳动物物种组成与植被的垂直分布是一致的。各地点的物种丰富度与单位面积（100 m²）树种平均丰富度、栖息地类型数和海拔高度相关。3个环境变量间也是相关的：海拔高度对单位面积树种平均丰富度和栖息地类型数有重要影响。根据研究结果提出两点保护建议：第一,保护区的移民迁出和退耕还林工程应首先在物种丰富度最高的九冲进行,而后是东溪和下谷;第二,为了增加个体流和基因流,保护区东西两片相间的非保护区地带应划入保护区,建立栖息地廊道。     

Diversity patterns of vascular epiphytes along an elevational gradient in the Andes

Aim To document the elevational pattern of epiphyte species richness at the local scale in the tropical Andes with a consistent methodology. Location The northern Bolivian Andes at 350–4000 m above sea level. Methods We surveyed epiphytic vascular plant assemblages in humid forests in (a) single trees located in (b) 90 subplots of 400 m² each located in (c) 14 plots of 1 ha each. The plots were separated by 100–800 m along the elevational gradient. Results We recorded about 800 epiphyte species in total, with up to 83 species found on a single tree. Species richness peaked at c. 1500 m and declined by c. 65% to 350 m and by c. 99% to 4000 m, while forests on mountain ridges had richness values lowered by c. 30% relative to slope forests at the same elevations. The hump‐shaped richness pattern differed from a null‐model of random species distribution within a bounded domain (the mid‐domain effect) as well as from the pattern of mean annual precipitation by a shift of the diversity peak to lower elevations and by a more pronounced decline of species richness at higher elevations. With the exception of Araceae, which declined almost monotonically, all epiphyte taxa showed hump‐shaped curves, albeit with slightly differing shapes. Orchids and pteridophytes were the most species‐rich epiphytic taxa, but their relative contributions shifted with elevation from a predominance of orchids at low elevations to purely fern‐dominated epiphyte assemblages at 4000 m. Within the pteridophytes, the polygrammoid clade was conspicuously overrepresented in dry or cold environments. Orchids, various small groups (Cyclanthaceae, Ericaceae, Melastomataceae, etc.), and Bromeliaceae (below 1000 m) were mostly restricted to the forest canopy, while Araceae and Pteridophyta were well represented in the forest understorey. Main conclusions Our study confirms the hump‐shaped elevational pattern of vascular epiphyte richness, but the causes of this are still poorly understood. We hypothesize that the decline of richness at high elevations is a result of low temperatures, but the mechanism involved is unknown. The taxon‐specific patterns suggest that some taxa have a phylogenetically determined propensity for survival under extreme conditions (low temperatures, low humidity, and low light levels in the forest interior). The three spatial sampling scales show some different patterns, highlighting the influence of the sampling methodology.     

Epiphytic bryophyte diversity and range distributions along an elevational gradient in Marojejy,Madagascar

Describing spatial variation in species richness and understanding its links to ecological mechanisms are complementary approaches for explaining geographical patterns of richness. The study of elevational gradients holds enormous potential for understanding the factors underlying global diversity. This paper investigates the pattern of species richness and range-size distribution of epiphytic bryophytes along an elevational gradient in Marojejy National Park, northeast Madagascar. The main objectives are to describe bryophyte species composition and endemism in Marojejy National Park, to describe the species richness and distribution patterns of epiphytic bryophytes along an elevational gradient from 250 m to 2050 m and to evaluate the explanatory value of environmental variables for the observed patterns. Bryophyte samples were collected following a nested design with four hierarchical levels: elevational belts, plots, quadrats, and microplots. In total, 254 epiphytic bryophyte species were recorded, comprising 157 liverworts and 97 mosses. Twenty-three of these are endemic to Madagascar. Species richness exhibits a hump-shaped pattern along the elevational gradient, peaking at 1,250 m. Eighty-seven percent of the total recorded species have a range distribution lower than 1,000 m, at which point 36% are restricted to these single elevations. Our results suggest that mean temperature, relative humidity, and vapor pressure deficit play important roles in shaping the richness pattern observed in this study. While the liverwort richness pattern did not correlate to vapor pressure deficit and responded only weakly to relative humidity, the richness pattern shown by mosses correlates well with mean temperature, relative humidity, and vapor pressure deficit.