Ecological Gradients in Diversity and Abundance: A Search for Patterns and Processes in Small Mammal Communities

The University of Kansas has long historical connections with Central America and the many Central Americans who have earned graduate degrees at KU. This work is part of the Central American Theses and Dissertations collection in KU ScholarWorks and is being made freely available with permission of the author through the efforts of Professor Emeritus Charles Stansifer of the History department and the staff of the Scholarly Communications program at the University of Kansas Libraries’ Center for Digital Scholarship.One of the most fundamental questions in ecology is: what are the patterns of diversity and the mechanisms that produce them? Many biological theories have been proposed to explain latitudinal and elevational diversity gradients, but no accepted, general explanation for the distribution of biodiversity has surfaced. Two necessities for establishing a general diversity theory are utilizing more rigorous statistical methods to test hypotheses, and including more comparative analyses. With these aims in mind, I examine the predictability of null models and biological diversity hypotheses for latitudinal and elevational gradients in diversity and abundance of small mammals. The unimodal distribution of diversity in North American desert rodents was highly consistent with the mid-domain effect—a spatial constraint null model incorporating the overlap of variably sized ranges within a bounded region. Deviations from the null model demonstrated a localized pulse in richness caused by a local hard boundary, the Baja peninsula. The small mammal diversity along an elevational transect in Costa Rica was unimodal with species richness highest between 1000-1300 m. The spatial constraints of montane topography appear to influence the diversity pattern, although climatic conditions including an intermediate rainfall and temperature regime, and distance from the persistent cloud cap also are correlated with the pattern. The global analysis of elevational diversity trends for non-volant small mammals revealed a ubiquitous pattern of mid-elevational peaks in species richness. The mid-domain null model was not generally predictive across all datasets. Diversity peaks occurred at higher elevations on taller mountains (Massenerhebung effect), which is consistent with climatic factors working in concert to produce elevationally correlated habitat bands. Gamma diversity patterns demonstrated higher altitudinal peaks in species diversity as latitude increased. An examination of replicates in alpha diversity studies along elevational transects found high variability both temporally and spatially, emphasizing the necessity of replication in well-designed studies of diversity gradients. In an examination of range size-abundance trends no strong relationship was found between abundance or body size with elevational range size. Local and regional abundances across elevational ranges generally revealed a trend toward higher abundances at mid-range, although usually not centered at the range midpoint

Forest Structure, above-Ground Carbon Stocks, and Productivity along an Elevational Gradient in the Ecuadorian Andes

The Andean forest provides a natural laboratory for evaluating long-term interactions between forests and variation in environmental parameters along elevational gradients. In particular, the mechanisms that control above-ground carbon stocks (AGC) and natural dynamics in mountain ecosystems constitute a potentially powerful tool for understanding the function of these ecosystems and their response to current climate change scenarios or past human disturbances. The present study integrates biotic (rarefied species richness and leaf traits) and abiotic (climate, soil properties and degradation) factors as possible drivers of AGC stocks, AGC net change (AGCnt), AGC productivity (AGCp) and AGC mortality (AGCk), along an elevational gradient of ca. 3000 m in the montane forests of the Ecuadorian Andes. My findings show that AGC metrics respond to elevational gradients (climate conditions) and past human disturbances. I found that temperature constitutes the primary filter for forest structure, AGC stocks, AGCnt and AGCp along the elevational gradient, where abiotic factors such as degradation and soil properties represent the main drivers for AGCk. This study provides insight into the processes that control patterns of AGC metrics in mountainous ecosystems, where temperature is likely the most important source of AGC variation in Andean forests

Determinants of above-ground carbon stocks and productivity in secondary forests along a 3000-m elevation gradient in the Ecuadorian Andes

Background: Secondary montane forests, covering 30% of forested lands in the Andes, play a crucial role in mitigating the impact of carbon release. However, the mechanisms responsible for carbon sequestration in the above-ground biomass of these forests are not well quantified. Aims: Understanding the determinants of above-ground carbon (AGC) dynamics in secondary forests along a 3000-m elevational gradient in the Andes to assess their mitigation potential. Methods: We assessed how abiotic and biotic conditions and past human disturbances were related to forest structure and composition, AGC stocks and productivity within sixteen 0.36-ha plots established in secondary forest stands of 30–35 years of age. Results: Structural equation models revealed that changes in temperature conditions along the elevation gradient shaped leaf functional composition, which in turn controlled AGC dynamics. Productivity and temperature decreased with increasing elevation and decreased tree community leaf area. Disturbance legacy (Tree mortality) increased with competitive thinning and low soil fertility. Conclusions: We show that temperature drives AGC dynamics by changing the functional trait composition. This highlights the importance of preserving these forests along elevation gradients and implies potentially strong future changes due to global warming.</p

Altitude and temperature drive anuran community assembly in a Neotropical mountain region

Understanding the spatial variation in species richness and the mechanisms that limit species range sizes along geographical gradients belong to the central research issues in macroecology. Here, we aim to test the topographic and climatic effects on anuran species richness and community composition in mountainous regions in the Brazilian Atlantic Forest biome. We used Individual-Based Rarefaction Curve (interpolation and extrapolation), Generalized Additive Model (GAM), Midpoint method and Principal Coordinates Analysis (PCoA) to analyze the topographic and climatic effects on anuran community composition, richness, and range sizes in a global biodiversity hotspot. Our results showed that altitude and annual mean temperature and temperature seasonality were the main drivers of species altitudinal range sizes and community assembly in mountainous regions. In conclusion, Anuran community richness peaked at intermediate altitudes following thus a hump-shaped pattern and corroborated the Rapoport's altitudinal rule as range sizes increased with altitude in mountainous regions from the Atlantic Forest biome. This study revealed new insights into the patterns and drivers of Neotropical anuran communities. Abstract in Portuguese is available with online material.Peer reviewe

Species richness of Orthoptera declines with elevation while elevational range of individual species peaks at mid elevation

Species richness has been shown to decrease, and elevational range increase (the Rapoport effect), with elevation as a consequence of biotic and abiotic factors, but patterns are inconsistent across taxonomic groups. Despite being an important indicator taxon and a component of local communities, Orthoptera distributions at higher elevations in Europe remain unclear. We investigated the relationship of Orthoptera species richness and elevational range with elevation in the Pyrenees mountains, Europe. We conducted sweepnetting surveys supplemented by hand-sampling, at 28 sites stratified by elevation, across three study areas. Using generalised linear models, we found that species richness declined with elevation. Elevation was an important predictor of species richness, but sampling effort and vegetation structure (height and cover) also contributed to estimates of species richness. Using a nonlinear regression to model the elevational range of species over the elevational gradient, we did not observe a Rapoport effect, with elevational range peaking at mid-elevation instead. Smaller elevational ranges of species found at high elevations may be due to a combination of sampling over a restricted elevational range and the presence of specialist high-elevation species. We argue that our findings are useful for understanding species distributions with elevation at the interface between local and regional scales. Clarifying the biotic and abiotic predictors of species distribution is important for informing conservation efforts and predicting consequences of climate change

Understory Epiphyte Hydrology: Analyzing water storage capacity of epiphytes along an elevational gradient in western Ecuadorian cloud forest

Epiphytes are defined as plants that grow on a host, often another plant, and acquire their nutrients and water from the atmosphere. As such is true, epiphyte composition is largely dependent upon atmospheric and thus climactic conditions. Due to high levels of atmospheric water availability that results from the frequent presence of mist, clouds, and high humidity, epiphytic plants grow and thus store water within the above ground region of the Andean cloud forest at levels higher than in any other ecosystem found in Ecuador. This study was done in hopes of revealing any trends of epiphytic water storage capacity along an elevational gradient within the western Ecuadorian cloud forest of the Santa Lucia Reserve. Individual trees were analyzed at 5 different elevations along an altitudinal gradient that spanned 1650 to 2270 meters. Within each analyzed tree, data was collected between approximately 5 and 7 meters above the ground. Vascular individuals were recorded to the family level, and moss coverage and moss thickness were estimated. Epiphytic growth was sampled from a standard 2500 cm2 region of each tree, and from this sample, water capacity (g/m2) was extrapolated. It was found that water capacity of mosses and other non-bromeliad epiphytes increased with elevation. Moss cover was also seen to increase with elevation, and moss thickness was seen to peak at roughly 2040 meters. An increase in water storage capacity was correlated with both an increase in moss cover as well as number of vascular epiphytes present within sampled trees. Changes in moss composition appeared to influence both vascular epiphytes and vascular individuals more generally. An increase in moss cover was correlated with an increase in number of vascular epiphytes, and an increase in moss thickness was correlated with an increase in number of vascular individuals, including climbers and epiphytes. It was speculated that as the level of water associated with moss is dependent upon how much is available in the surrounding environment, the change in moss composition that is correlated with a change in water capacity is due to climactic conditions that vary with elevation

Forest diversity in fragmented landscapes of northern Ethiopia and implications for conservation

Deforestation and habitat fragmentation that arise largely due to the conversion of forests to other agricultural land-use types and over-utilization of forest resources to satisfy the food and energy requirements of the increasing population are major environmental concerns in northern Ethiopia. Understanding plant species diversity and spatial distribution along environmental gradients is crucial in the management of the remnant forest ecosystems. However, the ecology of the forest remnants in northern Ethiopia is poorly studied. The purpose of this study is therefore to (i) investigate plant species diversity and natural regeneration in relation to selected environmental factors, (ii) quantify the elevation patterns of species diversity and community composition, (iii) examine the extent and spatial distribution pattern of standing dead stems and the effect of mass tree dieback on forest structure and diversity, and (iv) compare the regeneration response of Juniperus procera and Olea europaea subsp. cuspidata in an openaccess forest area to a closed forest management system. The study was conducted in the Desa’a and Hugumburda Afromontane forest remnants, which are the largest forest fragments in northern Ethiopia and are national forest priority areas. A total of 153 species belonging to 63 families was found in the study area; shrub and herb species dominate (ca. 70 %). The vegetation is mainly a dry Afromontane forest type with Juniperus and Olea as the dominant species; a riverine plant community in Hugumburda forest represents a moist forest type. Elevation, slope, soil depth, distance to the nearest stream, soil moisture, and forest disturbance are the main environmental factors influencing species distribution and partitioned plant communities. The diversity of species and the composition of plant communities in Desa’a forest significantly respond to elevation. Species richness and diversity show a unimodal, humpshaped relationship with elevation that peaked at mid elevation (1900 – 2200 m). The beta diversity values indicate medium species turnover along an elevational gradient. The percentages of dead standing trees (snags) due to natural disturbance at Desa’a forest are high for both J. procera (57 ± 7 %) and O. europaea subsp. cuspidata (60 ± 5 %), but show a decreasing trend with increasing elevation suggesting that restoration is more urgent at the lower elevations. Higher tree dieback at the lower elevation has pushed the tree species to the higher elevation by about 500 m, and this can lead to a shift in the forest-shrubland ecotone to higher elevations. Total stand density and basal area are reduced by 30 and 44 % when excluding snags of the two species, respectively. Thus, mass tree dieback of the two key species strongly influences the forest structure. High amounts of dead standing biomass are a particular risk in a fire-prone semi-arid forest environment, and controlling snag densities is of critical concern in the management of the remaining dry Afromontane forests in northern Ethiopia. The natural regeneration of native tree species in both forest remnants is low. Exclosure was found to be an effective management option to improve the regeneration of O. europaea, but it does not improve the regeneration of J. procera. Thus, a closed management system in the open-access and degraded forests may not guarantee a successful regeneration of native woody species. It rather favors grass and herbaceous species and can lead to a gradual conversion of the forest land to wooded grassland. Most of the seedlings in forest remnants are shrubs, while tree species are less diverse and abundant. The standing vegetation is only partly represented in the seedling bank and many of the rare tree species, e.g. Afrocarpus falcatus, show poor or no regeneration. A smaller number of saplings than mature individuals suggest that locally some forest species are experiencing extinction. Thus, it is important to give conservation priority to the last Afromontane forest remnants in northern Ethiopia to achieve local, national and international biodiversity conservation goals.Biodiversität in den Wäldern der fragmentierten Landchaften von Nordäthiopien und die Folgerungen für ihren Schutz Abholzung und die Fragmentierung der Lebensräume, hauptsächlich als Folge der Umwandlung der Wälder in andere landwirtschaftliche Nutzungen sowie die Ausbeutung der Waldressourcen, um den Nahrungsmittel- und Energiebedarf der wachsenden Bevölkerung zu befriedigen, verursachen erhebliche Umweltprobleme in Nordäthiopien. Kenntnisse der Pflanzenvielfalt und räumlichen Verteilung entlang Umweltgradienten ist entscheidend bei der Bewirtschaftung der verbleibenden Waldökosysteme. Jedoch ist die Ökologie der noch vorhandenen Waldfragmente in Nordäthiopien nur wenig untersucht. Das Ziel dieser Studie ist daher (i) die Vielfalt der Pflanzenarten und ihre natürliche Regeneration im Zusammenhang mit ausgewählten Umweltfaktoren zu untersuchen, (ii) die höhenabhängige Verteilung der Artenvielfalt und die Zusammensetzung der Pflanzengemeinschaften zu quantifizieren, (iii) das Ausmaß und die räumliche Verteilung stehender toter Baumstämme sowie die Auswirkungen eines Baumsterbens auf die Waldstruktur und -vielfalt zu untersuchen, und (iv) den Einfluss eines geschlossenen Waldbewirtschaftungssystems mit dem eines zugänglichen Waldes auf die Regeneration von Juniperus procera und Olea europaea subsp. cuspidata zu vergleichen. Die Studie wurde in den afromontanen Wäldern Desa’a und Hugumburda, die größten Waldfragmente in Nordäthiopien und mit nationaler Schutzpriorität, durchgeführt. Insgesamt 153 Arten aus 63 Familien kommen im Untersuchungsgebiet vor; Strauch- und Kräuterarten dominieren (ca. 70 %). Die Vegetation ist hauptsächlich vom trockenen afromontanen Waldtyp mit den dominierenden Arten Juniperus und Olea; eine gewässernahe Pflanzengesellschaft im Hugumburda Wald ist vom Typ Feuchtwald. Höhenlage, Hangneigung, Bodentiefe, Nähe zum nächsten Kleingewässer, Bodenfeuchte und anthropogene Störungen sind die wichtigsten Umweltfaktoren, die die Artenverteilung und die Zusammensetzung der Pflanzengesellschaften beeinflussen. Die Artenvielfalt und die Zusammensetzung der Pflanzengesellschaften in Desa’a Wald sind signifikant abhängig von der Höhenlage. Artenreichtum und Diversität bilden eine unimodale Beziehung mit der Höhenlage; der höchste Wert ist bei einer mittleren Höhenlage (1900 - 2200 m). Die Betadiversitätswerte deuten auf einen mittleren Artenwechsel entlang eines Höhengradienten hin. Die Anteile stehender toter Baumstämme als Folge natürlicher Störungen im Desa’a Wald sind hoch, sowohl für J. procera (57 ± 7 %) als auch für O. europaea subsp. cuspidata (60 ± 5 %), zeigen jedoch einen abnehmenden Trend mit zunehmender Höhenlage, was darauf hindeutet, dass Rekultivierungsmaßnahmen in den unteren Höhenlagen dringender sind als in höheren. Das stärkere Baumsterben in den unteren Höhenlagen hat dazu geführt, dass das Vorkommen der betroffenen Baumarten sich um ca. 500 m nach oben verschoben hat. Dies kann auch zu einer Verschiebung der Wald-Buschland-Vegetation in höhere Lagen führen. Bestandsdichte bzw. Basalfläche sind um 30 bzw. 44 % reduziert wenn die stehenden toten Individuen der beiden Arten nicht berücksichtigt werden; das Absterben der beiden Hauptbaumarten beeinflusst also stark die Waldstruktur. Große Mengen toter Baumbiomasse sind ein besonderes Waldbrandrisiko in einem semiariden Wald und die Kontrolle der Dichte des Totholzes ist von entscheidender Bedeutung bei der Bewirtschaftung der noch verbleibenden trockenen afromontanen Wälder in Nordäthiopien. Die natürliche Regeneration der einheimischen Baumarten in den beiden untersuchten Waldfragmenten ist niedrig. Es zeigt sich, dass eingezäunte Flächen eine wirksame Bewirtschaftungsoption sind, um die Regeneration von O. europaea zu begünstigen. Diese Maßnahme bleibt jedoch ohne Wirkung auf J. procera. Daher würde ein Bewirtschaftungssystem mit Zugangsbeschränkungen in den offenen, degradierten Wäldern eine erfolgreiche Regeneration der einheimischen Holzgewächse nicht garantieren. Es werden eher Gras- und Kräuterarten begünstigt, was zu einer langsamen Umwandlung des Waldes in Grasland mit Gehölzen führen kann. Die meisten Keimlinge in den Waldfragmenten sind von Straucharten, während Baumarten weniger vielfältig bzw. zahlreich sind. Die bestandsbildenden Arten sind nur zum Teil in der Samenbank vertreten, und viele der seltenen Arten, z. B. Afrocarpus falcatus, zeigen wenig bzw. gar keine Regeneration. Die geringe Bedeutung von Jungwuchs im Vergleich zu den voll ausgewachsenen Baumindividuen deutet daraufhin, dass lokal einige bestandsbildenden Baumarten aussterben könnten. Daher muss den letzten afromontanen Waldfragmenten in Nordäthiopien eine hohe Schutzpriorität eingeräumt werden, auch um die lokalen, nationalen und internationalen Ziele zum Schutze der Artenvielfalt zu erreichen

Evaluating the potential of full-waveform lidar for mapping pan-tropical tree species richness

AIM: Mapping tree species richness across the tropics is of great interest for effective conservation and biodiversity management. In this study, we evaluated the potential of full‐waveform lidar data for mapping tree species richness across the tropics by relating measurements of vertical canopy structure, as a proxy for the occupation of vertical niche space, to tree species richness. LOCATION: Tropics. TIME PERIOD: Present. MAJOR TAXA STUDIED: Trees. METHODS: First, we evaluated the characteristics of vertical canopy structure across 15 study sites using (simulated) large‐footprint full‐waveform lidar data (22 m diameter) and related these findings to in‐situ tree species information. Then, we developed structure–richness models at the local (within 25–50 ha plots), regional (biogeographical regions) and pan‐tropical scale at three spatial resolutions (1.0, 0.25 and 0.0625 ha) using Poisson regression. RESULTS: The results showed a weak structure–richness relationship at the local scale. At the regional scale (within a biogeographical region) a stronger relationship between canopy structure and tree species richness across different tropical forest types was found, for example across Central Africa and in South America [R^{2} ranging from .44–.56, root mean squared difference as a percentage of the mean (RMSD%) ranging between 23–61%]. Modelling the relationship pan‐tropically, across four continents, 39% of the variation in tree species richness could be explained with canopy structure alone (R^{2} = .39 and RMSD% = 43%, 0.25‐ha resolution). MAIN CONCLUSIONS: Our results may serve as a basis for the future development of a set of structure–richness models to map high resolution tree species richness using vertical canopy structure information from the Global Ecosystem Dynamics Investigation (GEDI). The value of this effort would be enhanced by access to a larger set of field reference data for all tropical regions. Future research could also support the use of GEDI data in frameworks using environmental and spectral information for modelling tree species richness across the tropics