Papers by Michael Kessler
Proceedings of the National Academy of Sciences of the United States of America, 2015
The high species richness of tropical forests has long been recognized, yet there remains substan... more The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of…
A norbornene-based cross-linker was synthesized and mixed at different loadings with two separate... more A norbornene-based cross-linker was synthesized and mixed at different loadings with two separate monomers for self-healing polymer applications: 5-ethylidene-2-norbornene (ENB) and endo-dicyclopentadiene (endo-DCPD). The monomer/cross-linker systems were polymerized by ring-opening metathesis polymerization (ROMP) with Grubbs' catalyst. The thermal-mechanical properties of the polymerized networks were evaluated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) and the curing process was monitored by parallel plate oscillatory rheometry. The viscosities of the pre-polymer blends are shown to be adequately low for self-healing, and exhibit a high ROMP reactivity to form cross-linked networks with enhanced thermal-mechanical properties. The addition of cross-linker increases the glass transition temperature (T g ) and the storage modulus both above and below T g . The storage modulus increase above T g is used to estimate the molecular weight (M c ) between entanglements or cross-link sites for both ENB and endo-DCPD-based networks. The crosslinker also greatly accelerates network formation as defined by the gelation time.
Effects of Simulated Climate Change on Biomass Allocation Patterns of Seedlings of Two Andean Lepidium Species (Brassicaceae) with Different Elevational Distributions
pected to lead to increasing temperatures and lifting of cloud condensation layers, possibly also... more pected to lead to increasing temperatures and lifting of cloud condensation layers, possibly also establishing new biotic interactions. These events are likely to force species to either migrate upwards or to adapt to changed environmental conditions (Pounds et al. 1999). It is likely that the migratory response of some species will not be fast enough to encompass climate change (Bush 2002), and will be hampered by habitat loss and fragmentation, or simply by the maximum height of mountain ranges, increasing the number of species in danger of extinction (Thomas et al. 2004). Even species able to migrate are unlikely to encounter identical climatic conditions at higher elevations, because climate change does not simply imply an increase of temperatures but also shifts in precipitation regimes, cloudiness, and especially the frequency of extreme environmental conditions such as droughts and frost (Vuille et al. 2003). It is therefore likely that all species will be forced to some degree to adjust their autoecological behavior. Optimal partioning models and theories suggest that plants respond to variation in the environment by allocating biomass among plant organs to optimize the capture of nutrients, light, water and CO2 in a manner that maximizes plant growth rates (Bazzaz 1996, McConnaughay & Coleman 1999). Thus the study of the biomass allocation patterns of plant species of tropical mountains at different elevations can indicate how adaptable the species will be to climate change. Little is known about the responses of tropical montane plants to climatic change under field conditions. To date, only one field study has been done to test the predicted effects of climate change on tropical montane epiphyte plant communities (Nadkari & Solano 2002), and comparable studies for other life forms or in other high mountain ecosystems such as puna and páramo are completely lacking. The purpose of the present study was to document how the biomass allocation patterns of seedlings of two high-Andean plant species react to a simulated global warming under field condition. For one species we simulated the move to higher elevations, for the other the shift was to lower elevations. We concentrated on the establishment and juvenile stages due to their relevance in the establishment and maintenance of populations (Harper 1977) and susceptibility to environmental stress (Larcher 1994).
Conservation Value of Logging Concession Areas in the Tropical Rainforest of the Korup Region, Southwest Cameroon
Tropical rainforests are home for renewable natural resources for living and non living things. T... more Tropical rainforests are home for renewable natural resources for living and non living things. The dynamic and interdependent nature of tropical rainforest components make it a fragile ecosystem and the scale in which human exercise pressure on these forests has increased over the past decades. Extraction of valuable trees for commercial purpose and other logging activities in tropical rainforest has mainly contributed to the reduction of the size of the rainforest belt. Furthermore, current levels of wildlife exploitation in many parts of tropical West and Central Africa pose serious threats to wildlife populations. While the "bushmeat problem" is one of the major problems in conservations science and management, there are few experiences with wildlife management in tropical rainforests at all, and most of the biological and social pre-conditions for a successful application remain obscure. The broad aims of this study are to evaluate the conservation value of logging concession areas of the Korup region through the assessment of tree communities and wildlife populations and to propose a conservation management concept for wildlife in the region. Many studies are dealing with the effects of selective logging on tree communities, but few studies have attempted to analyse effects of logging at different scale levels and analysed vegetation composition in logged areas in detail. We studied tree assemblages in forests adjacent to Korup National Park in the Southwest of Cameroon. A total of 168 plots of 50 m x 50 m (0.25 ha) were systematically distributed along 24 two-km transects situated within four 16 km2 study areas, of which two were in 10 years-old heavily logged forests and two in relatively undisturbed primary (unlogged) forests. Beside the vegetation, primates and hornbills are described to play an important role in the maintenance of tropical forests and the food resources constitute one of the most limiting factors for most wildlife species including primates and hornbills. We investigated food resources for primates and hornbills following the plot, transect and study site design. In addition we studied the population development of eight primate and two hornbill species using the line transect and the Distance sampling models. A total of 9,134 trees (dbh . 8.0 cm) belonging to 217 species and 55 families were recorded. Community parameters of trees were analysed at plot, transect and study site levels, and compared between logged and unlogged forests. Tree abundance was relatively lower (about 38%) in logged forests compared to unlogged forests. Tree species richness was least affected at the largest sampling scale (16-km2 study site). Species richness was reduced from 188 species (Jackknife index= 208 spp.) to 177 species (Jackknife= 213 spp.) at smaller spatial scales, a reduction of 6%. Along the 2-km transects, an average of 87.5 ( } 5.0) species were found in unlogged compared to 68.5 (±3.0) species in logged forest (reduction of 32%). At plot level (50 x 50 m), 32.4 (±7.6) species were found in unlogged and 22.2 (±5.7) species in logged forest (reduction of 31%). However, species composition differed markedly between logged and unlogged forests as was shown by two-dimensional ordination of the tree assemblages at species level. An analysis at family level, including the twenty one most abundant tree families did not show significant differences in family importance values (FIV) between unlogged (FIV= 222.58 and 221.51) and logged (FIV= 207.52 and 214.64) study sites, suggesting that logging effects are rather at species than at family level. Food trees were relatively more abundant in unlogged forests (2,556 food trees recorded) compared to logged forests (1,864 trees recorded). Primates population densities differed from one species to another but also from unlogged and logged study sites. The C. mona, C. nictitans nictitans, C. pogonias, C. torquatus and P. troglodytes population densities were relatively high in logged (28.73 ind./km2; 23.35 ind./km2; 1.03 ind./km2; 6.65 ind./km2; and 2.03 ind.km2 respectively) forests study sites compared to unlogged (15.24 ind./km2; 17.90 ind./km2; 0.31 ind./km2; 1.01 ind.km2; and 0.02 ind.km2 respectively) forest study sites. C. erythrotis had high estimates in unlogged forests (17.55 ind./km2 ) compared to logged forests (10.93 ind./km2) study sites. However the preuss fs red colobus (P. pennantii preussi) was not observed in logged forest study sites and was estimated at very low density (0.02 ind.km2) in unlogged forest study sites. Compared with earlier studies, the drill (M. leucophaeus) population density has relatively increased in unlogged (1.03 ind.km2) and in logged (0.91 ind./km2). The black-casqued hornbill (C. atrata) population was relatively higher in logged forest study sites (23.15 ind./km2) compared to unlogged forest study sites (21.61 ind./km2). However, the brown-checked hornbill (C. cylindricus) population density was relatively…
Biodiversity continues to decline in the face of increasing anthropogenic pressures such as habit... more Biodiversity continues to decline in the face of increasing anthropogenic pressures such as habitat destruction, exploitation, pollution and introduction of alien species. Existing global databases of species’ threat status or population time series are dominated by charismatic species. The collation of datasets with broad taxonomic and biogeographic extents, and that support computation of a range of biodiversity indicators, is necessary
Toxicology Letters, 2011
Silver nanoparticles (Ag-NPs) are the most frequent commercialized nanomaterial currently. Due to... more Silver nanoparticles (Ag-NPs) are the most frequent commercialized nanomaterial currently. Due to a distinct lack of information on hazardous properties of Ag-NPs in human cells, a study was conducted to evaluate Ag-NP induced DNA damage, cell death and functional impairment in human mesenchymal stem cells (hMSCs). Initially, Ag-NPs and their cellular distribution were characterized by transmission electron microscopy (TEM). Ag-NPs were exposed to hMSCs for 1, 3 and 24 h. Cytotoxicity was measured by the trypan blue exclusion test and the fluorescein-diacetate test, DNA damage was evaluated by the comet assay and chromosomal aberration test. Cytokine release of IL-6, IL-8 and VEGF was observed using the ELISA technique. Additionally, hMSC migration capability was tested in a transwell system. TEM revealed a Ag-NP distribution to cytoplasm and nucleus. Cytotoxic effects were seen at concentrations of 10 g/ml for all test exposure periods. Both, comet assay and chromosomal aberration test showed DNA damage after 1, 3, and 24 h at 0.1 g/ml. A significant increase of IL-6, IL-8 and VEGF release indicates hMSC activation. Migration ability was not impaired at subtoxic concentrations. In conclusion, we demonstrated cyto-and genotoxic potential of Ag-NPs in hMSCs at significantly higher concentrations as compared to antimicrobial effective levels.
Toxicology in Vitro, 2011
Despite increasing application of zinc oxide nanoparticles (ZnO-NPs) for industrial porpuses, dat... more Despite increasing application of zinc oxide nanoparticles (ZnO-NPs) for industrial porpuses, data about potential toxic properties is contradictory. The current study focused on the cyto-and genotoxicity of ZnO-NPs in comparison to ZnO powder in primary human nasal mucosa cells cultured in the air-liquid interface. Additionally, IL-8 secretion as a marker for pro-inflammatory effects was measured. Particle morphology and intracellular distribution were evaluated by transmission electron microscopy (TEM). ZnO-NPs were transferred into the cytoplasm in 10% of the cells, whereas an intranuclear distribution could only be observed in 1.5%. While no cyto-or genotoxicity could be seen for ZnO powder in the dimethylthiazolyl-diphenyl-tetrazolium-bromide (MTT) test, the trypan blue exclusion test, and the singlecell microgel electrophoresis (comet) assay, cytotoxic effects were shown at a ZnO-NP concentration of 50 lg/ml (P < 0.01). A significant enhancement in DNA damage was observed starting from ZnO-NP concentrations of 10 lg/ml (P < 0.05) in comparison to the control. IL-8 secretion into the basolateral culture medium was increased at ZnO-NP concentrations of 5 lg/ml (P < 0.05), as shown by ELISA. Our data indicates cyto-and genotoxic properties as well as a pro-inflammatory potential of ZnO-NPs in nasal mucosa cells. Thus, caution should be taken concerning their industrial and dermatological application. Additionally, further investigation on repetitive NP exposure is needed to estimate the impact of repair mechanisms.
Proceedings of the National Academy of Sciences, 2007
Losses of biodiversity and ecosystem functioning due to rainforest destruction and agricultural i... more Losses of biodiversity and ecosystem functioning due to rainforest destruction and agricultural intensification are prime concerns for science and society alike. Potentially, ecosystems show nonlinear responses to land-use intensification that would open management options with limited ecological losses but satisfying economic gains. However, multidisciplinary studies to quantify ecological losses and socioeconomic tradeoffs under different management options are rare. Here, we evaluate opposing land use strategies in cacao agroforestry in Sulawesi, Indonesia, by using data on species richness of nine plant and animal taxa, six related ecosystem functions, and on socioeconomic drivers of agroforestry expansion. Expansion of cacao cultivation by 230% in the last two decades was triggered not only by economic market mechanisms, but also by rarely considered cultural factors. Transformation from near-primary forest to agroforestry had little effect on overall species richness, but redu...
PLoS ONE, 2012
Managing ecosystems for carbon storage may also benefit biodiversity conservation, but such a pot... more Managing ecosystems for carbon storage may also benefit biodiversity conservation, but such a potential 'win-win' scenario has not yet been assessed for tropical agroforestry landscapes. We measured above-and below-ground carbon stocks as well as the species richness of four groups of plants and eight of animals on 14 representative plots in Sulawesi, Indonesia, ranging from natural rainforest to cacao agroforests that have replaced former natural forest. The conversion of natural forests with carbon stocks of 227-362 Mg C ha 21 to agroforests with 82-211 Mg C ha 21 showed no relationships to overall biodiversity but led to a significant loss of forest-related species richness. We conclude that the conservation of the forestrelated biodiversity, and to a lesser degree of carbon stocks, mainly depends on the preservation of natural forest habitats. In the three most carbon-rich agroforestry systems, carbon stocks were about 60% of those of natural forest, suggesting that 1.6 ha of optimally managed agroforest can contribute to the conservation of carbon stocks as much as 1 ha of natural forest. However, agroforestry systems had comparatively low biodiversity, and we found no evidence for a tight link between carbon storage and biodiversity. Yet, potential win-win agroforestry management solutions include combining high shade-tree quality which favours biodiversity with cacao-yield adapted shade levels.
Plant Systematics and Evolution, 2007
As a member of the Sanguisorbinae, taxonomically complicated Polylepis Ruiz & Pav. from the South... more As a member of the Sanguisorbinae, taxonomically complicated Polylepis Ruiz & Pav. from the South American Andes is one of the few wind-pollinated genera of Rosaceae. Here, it is suggested that problems traditionally faced in species delimitation and phylogeny reconstruction may be in part due to a combination of weak reproductive barriers and the large distances that can be covered by genetic information as a result of wind pollination. The pattern of species distribution as well as molecular data (AFLP) of Polylepis were contrasted with those of an unrelated, insectpollinated genus of similar species number and distribution, Minthostachys (Griseb.) Spach (Lamiaceae). In the present case, extensive pollen-mediated gene flow may explain the homogenization of genetic variability over larger distances and a lower number of species restricted to individual countries in the wind-pollinated genus Polylepis, but more examples will have to be studied before arriving at final conclusions.
Journal of Thermal Analysis and Calorimetry, 2007
The addition of suitable cross-linking agents with norbornene-based monomers has significant effe... more The addition of suitable cross-linking agents with norbornene-based monomers has significant effects on the thermal properties of the resulting polymers formed by olefin metathesis. Ethylidene norbornene (ENB) and endo-dicyclopentadiene (endo-DCPD) were mixed separately with various loadings of three different cross-linking agents and then polymerized with the addition of Grubbs' catalyst. The polymerization kinetics and resulting glass transition temperature (T g ) of the systems were evaluated by differential scanning calorimetry (DSC). The addition of the first cross-linking agent, norbornadiene (CL-1), to both endo-DCPD and ENB resulted in decreasing glass transition temperatures with increasing concentrations. In contrast, the addition of the other two cross-linking agents (CL-2 and CL-3), which were both custom synthesized bifunctional norbornyl systems, to both endo-DCPD and ENB resulted in a monotonic increases in T g with cross-linker concentration. By tailoring the loading of these custom cross-linking agents, the properties of these polymer systems can be controlled for various applications, including self-healing composites.
Journal of Applied Polymer Science, 2009
Bio-based resins are an alternative to petroleum-based resins in the production of fiber-reinforc... more Bio-based resins are an alternative to petroleum-based resins in the production of fiber-reinforced polymers (FRPs) by processes such as pultrusion. A detailed understanding of the cure behavior of the resin is essential to determine the process variables for production of FRPs. In this work, the cure kinetics of soybean oil-styrene-divinylbenzene thermosetting polymers is characterized by differential scanning calorimetry (DSC) measurements. By varying the concentration of the cationic initiator from 1 to 3 weight percent (wt %), the most viable resin composition for pultrusion is identified. The ability of phenomenological reaction models to describe the DSC measurements for the optimum resin composition is tested and kinetic equations, which can be used to determine the degree of cure at any temperature and time, are determined. V
Global Ecology and Biogeography, 2007
Aim To search for differences in the spatial variability of upper and lower elevational distribut... more Aim To search for differences in the spatial variability of upper and lower elevational distribution limits of tropical ferns, based on the assumption that these are determined to different degrees by biotic and abiotic factors. Location The Yungas biogeographical region, in the Bolivian Andes. Methods From a data base of > 25,000 herbarium records, we analysed the skewness of the elevational distribution of 220 montane pteridophyte species, each with ≥ 15 records. Additionally, we compared the spatial variability of upper and lower elevational range limits of ferns in 351 plots of 400 m 2 each along four elevational transects separated by 15-450 km. Individual species showed variable elevational distribution patterns, ranging from symmetric to asymmetric, i.e. downward and upward skewed, but overall there was a statistically significant trend towards asymmetric distributions with abrupt upper limits and diffuse lower limits. This trend, however, was almost exclusively due to terrestrial species occurring at and above the current timberline. The analysis of the elevational transects revealed no significant trends. The downward-skewed distributional abundance of terrestrial, open-country ferns near the timberline appears to be a result of the extensive forest destruction that has lowered the timberline in the high Andes by 500 -800 m, opening up habitats for a restricted suite of species. Our study shows that a limited number of species can cause a general trend in the overall data set, and that failure to extract these data may result in unsupported conclusions, in our case to assign a greater importance to biotic and abiotic factors in the elevational limitation of plants at lower and upper elevations, respectively.
Nanosized titanium dioxide particles do not induce DNA damage in human peripheral blood lymphocytes
Environmental and Molecular Mutagenesis, 2010
Industrial application of titanium dioxide nanoparticles (TiO(2) -NPs) as an additive in pharmace... more Industrial application of titanium dioxide nanoparticles (TiO(2) -NPs) as an additive in pharmaceutical and cosmetic products is increasing. However, the knowledge about the toxicity of this material is still incomplete and data concerning health and environmental safety and results of recent studies on TiO(2) nanotoxicology are inconsistent. The in vitro geno- and cytotoxicity of TiO(2) -NPs in the anatase crystal phase was evaluated in human peripheral blood lymphocytes from 10 male donors. Initially, transmission electron microscopy (TEM) was performed to describe particle morphology and size, the degree of particle aggregation, and the intracellular distribution. Cells were exposed to nanoparticles in increasing concentrations of 20, 50, 100, and 200 μg/ml for 24 hr. Cytotoxic effects were analyzed by trypan blue exclusion test and the single-cell microgel electrophoresis (comet) assay was applied to detect DNA double-strand breakage. TiO(2) -NPs were sphere shaped with a diameter of 15-30 nm. Despite dispersive pretreatment, a strong tendency to form aggregates was observed. Particles were detected in the cytoplasm of lymphocytes, but also a transfer into the nucleus was seen. The trypan blue exclusion test did not show any decrease in lymphocyte viability, and there was no evidence of genotoxicity in the comet assay for any of the tested concentrations. In conclusion, TiO(2) -NPs reached the cytoplasm as well as the nucleus and did not induce cyto- or genotoxic effects in human peripheral blood lymphocytes. Complement investigations on different human cell systems will be performed to estimate the biocompatibility of TiO(2) -NPs. Environ. Mol. Mutagen.
Ecological Modelling, 2010
The quality of climate models has largely been overlooked as a possible source of uncertainty tha... more The quality of climate models has largely been overlooked as a possible source of uncertainty that may affect the outcomes of species distribution models, especially in the tropics, where comparatively few climatic stations are available. We compared the geographical discrepancies and potential conservation implications of using two different climate models (Saga and Worldclim) in combination with the species modelling approach Maxent in Bolivia. We estimated ranges of selected bird and fern species biogeographically restricted to either humid montane forest of the northern Bolivian Andes or seasonal dry tropical forests (in the Andes and southern lowlands). Saga and Worldclim predicted roughly similar climate patterns of temperature that were significantly correlated. Precipitation layers of both climate models were also roughly similar, but showed important differences. Species ranges estimated with Worldclim and Saga likewise produced different results. Ranges of species endemic to humid montane forests estimated with Saga had higher AUC (Area under the curve) values than those estimated with Worldclim, which for example predicted the occurrence of humid montane forest bird species near Lake Titicaca, an area that is clearly unsuitable for these species. Likewise, Worldclim overpredicted the occurrence of fern and bird species in the lowlands of the Chapare region and well south of the Andean Elbow, where more seasonal biomes occur. By contrast, Saga predictions were coherent with the known distribution of humid montane forests in the northern Bolivian Andes. Estimated ranges of species endemic to seasonal dry tropical forests predicted with Saga and Worldclim were not statistically different in most cases. However, detailed comparisons revealed that Saga was able to distinguish fragments of seasonal dry tropical forests in rain-shadow valleys of the northern Bolivian Andes, whereas Worldclim was not. These differences highlight the neglected influence of climate layers on modelling results and the importance of using the most accurate climate data available when modelling species distributions.
Ecography, 2005
A monotonic decline in species richness with increasing elevation has often been considered a gen... more A monotonic decline in species richness with increasing elevation has often been considered a general pattern, but recent evidence suggests that the dominant pattern is hump-shaped with maximum richness occurring at some mid-elevation point. To analyse the relationship between species richness and elevation at a local scale we surveyed birds from lowlands to timberline in the Bolivian Andes. We divided the transect into 12 elevational belts of 250 m and standardized species richness in each belt with both individual-and sample-based rarefaction and richness estimation. The empirical data were then correlated to four explanatory variables: 1) area per elevational belt, 2) elevation (also representing ecosystem productivity), 3) a middomain effect (MDE) null model of geometrically constrained empirical range sizes, and 4) a hump-shaped model derived empirically for South American birds representing the regional species pool hypothesis. Local species richness peaked at ca 1000 m elevation, declined sharply to ca 1750 m, and then remained roughly constant. Elevation was the best single predictor, accounting for 78 Á/85% of the variance in the empirical data. A multiple regression model with elevation, area, and MDE explained 85 Á/90% of the variance. Monte Carlo simulations showed that the richness peak at 1000 m is the result of an overlap of two distinct avifaunas (lowland and highland) and that the correlation to MDE in the multiple regression was likely spurious. We recommend complementing correlation analyses involving MDE predictions with an examination of the distribution of range midpoints. The steep decline at mid-elevations was mainly due to a rapid loss of lowland species. The high-elevation plateau is striking and unexpected, but has also been found previously. It cannot be explained at present and exemplifies that despite several decades of research elevational gradients are still not well understood.
Diversity and Distributions, 2001
We studied the patterns of species richness and range-size rarity (as a measure of endemism) of t... more We studied the patterns of species richness and range-size rarity (as a measure of endemism) of two plant groups (Pteridophyta, Bromeliaceae) and birds along two gradients of elevation, humidity and human land use in a forested Andean valley. Both transects covered the transition from an arid valley bottom through a cloud forest zone to relictual high-elevation Polylepis forest, but transects differed in overall precipitation. Plants were surveyed in 88 plots of 400 m 2 each, while birds were detected primarily through visual observations and tape recordings over areas of 0.3-1.5 km 2 . Global range sizes of all species were mapped on 1 ° -grids and rangesize rarity was calculated as the mean inverse range size of all species recorded in elevational steps of 200 m. Patterns of species richness and range-size rarity were mainly unrelated between and within study groups. Monotonic increases and decreases and hump-shaped patterns were observed for species richness as well as range-size rarity. Several of these patterns can be interpreted in the light of the ecological requirements of each taxonomic group, e.g. dependence of fern species richness on humidity or of bird richness on habitat complexity. Species richness of ferns and birds peaked at higher elevations along the less rainy transect, possibly as a result of higher levels of solar radiation and ecosystem productivity. Patterns of species richness and endemism of the study groups are causally unrelated and cannot be used to predict those of other groups at the spatial scale of this study. Human impact was highest in areas of mostly low to intermediate species richness, but was often high in zones of high endemism.
Diversity and Distributions, 2007
ABSTRACTUse of β‐diversity indices in the study of spatial distribution of species diversity is h... more ABSTRACTUse of β‐diversity indices in the study of spatial distribution of species diversity is hampered by the difficulty of applying significance tests. To overcome this problem we used a simulation approach in a study of species turnover of ferns, aroids, bromeliads, and melastomes along an elevational gradient from 1700 m to 3400 m in a species‐rich tropical cloud forest of Bolivia. Three parameters of species turnover (number of upper/lower elevational species limits per elevational step, Wilson–Shmida similarity index between adjacent steps) were analysed. Significant species turnover limits were detected at 2000 (± 50) m and 3050 m, which roughly coincided with the elevational limits of the main vegetation types recognized in the study area. The taxon specificity of elevational distributions implies that no single plant group can be used as a reliable surrogate for overall plant diversity and that the response to future climate change will be taxon‐specific, potentially leadi...
Biological Conservation, 2011
Tropical species with narrow elevational ranges may be thermally specialized and vulnerable to gl... more Tropical species with narrow elevational ranges may be thermally specialized and vulnerable to global warming. Local studies of distributions along elevational gradients reveal small-scale patterns but do not allow generalizations among geographic regions or taxa. We critically assessed data from 249 studies of species elevational distributions in the American, African, and Asia-Pacific tropics. Of these, 150 had sufficient data quality, sampling intensity, elevational range, and freedom from serious habitat disturbance to permit robust across-study comparisons. We found four main patterns: (1) species classified as elevational specialists (upper-or lower-zone specialists) are relatively more frequent in the American than Asia-Pacific tropics, with African tropics being intermediate; (2) elevational specialists are rare on islands, especially oceanic and smaller continental islands, largely due to a paucity of upper-zone specialists; (3) a relatively high proportion of plants and ectothermic vertebrates (amphibians and reptiles) are upper-zone specialists; and (4) relatively few endothermic vertebrates (birds and mammals) are upperzone specialists. Understanding these broad-scale trends will help identify taxa and geographic regions vulnerable to global warming and highlight future research priorities.
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Papers by Michael Kessler