Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Resumen:

Projected climate warming will potentially cause profound modifications of ecosystems worldwide, including large redistribution of biodiversity. Among the ecosystems that react most sensitive to climatic changes are tropical mountain rain forests. An essential step to conserve these ecosystems is to study the response of their biodiversity to changing climate conditions. For this purpose elevational gradients are particular suitable. Furthermore, it is important to consider a topographical gradient because of the rugged mountainous study area. Species richness, the commonly used measure for biodiversity, only describes parts of biodiversity. Therefore, it is crucial to additionally study phylogenetic and functional diversity to detect impacts of climate change on ecosystem functions. Hence, the aim of the study was to investigate the influence of an elevational and a topographical gradient on species richness, phylogenetic diversity (PD) and functional composition of two traits, specific leaf area (SLA) and wood specific gravity (WSG), taking tree communities as example. Additionally, I measured the phylogenetic signal of the traits to expose if they are conserved or convergent. By the combination of PD and trait based methods community assembly patterns were detected and furthermore, it was tested if PD mirrors the functional diversity. The results showed no change in rarefied species richness with elevation. In contrast, PD increased from low to mid elevation and decreased from mid to high elevation. The topographical gradient also had an influence on PD. The functional composition of SLA and WSG changed with elevation and partly with topographic position. While SLA values decreased from low to high elevation and were lower on the upper slopes at mid and high elevation, WSG values at high elevation were overall high with a lower range but did not change with topographic position. Both traits appeared to be convergent. Considering the detected trait convergence, it is likely that competitive interactions shape the community at low elevation whereas at high elevation environmental filtering probably is the main assembly process. Furthermore, filtering effects on the upper slope at mid elevation could be exposed. The functional composition of SLA and WSG indicated biotic filters, like competition for light, at low elevation and abiotic stress filters at high elevation. Moreover, a filtering effect of the topographical gradient on SLA on the upper slope at mid and high elevation was detected. Overall, the PD uncovered more facets of the biodiversity than species richness. However, the addition of trait based methods is important to confirm assembly patterns detected by PD and to detect further underlying processes.

Resumen:

Natural ecosystems across the globe are already modified in their structure and composition. This often leads to a decline of biodiversity which can in turn affect important ecological functions. Species richness as a measure of biodiversity ignores almost 89% of the overall diversity and many traits of species show a phylogenetic signal. Therefore, phylodiversity is often a better indicator of functional processes than species richness. To better understand changes in ecosystem functionality it is thus essential to study and compare taxonomic and phylogenetic diversity patterns across environmental gradients such as elevation. In this study I therefore analyse the effects of elevation and soil parameters on the taxonomic and phylogenetic diversity of tree communities in an Andean mountain rainforest in southern Ecuador. 427 tree species were recorded on 54 plots at three elevation levels at 1000, 2000 and 3000 m, with phyloalpha diversities ranging between -1.91 and 2.20. There was no distinct pattern of over- or underdispersed phyloalpha diversities along the gradient. Elevation affected both the alpha taxonomic and phylogenetic tree species diversity: While taxonomic diversity declined along the elevation gradient, phyloalpha diversity showed a humped relationship with highest phylodiversity values at mid-elevations. I assume environmental filtering to reduce the taxonomic diversity at high elevation. Simultaneously, I suppose the occurrence of facilitator species to enable a nevertheless phylogenetic diverse tree community to persist at high elevations. At low elevations my findings indicate neutral or stochastic processes to shape the phyloalpha dispersion. Elevation had the strongest direct effect on the phyloalpha diversities. Moreover, it influenced soil parameters which explained an additional amount of the phyloalpha diversities. The pattern of phylobeta diversity supported the idea of facilitator species at high elevations and revealed two phylogenetic distantly related tree communities to exist at low and high elevation levels. The ranges of both species sets overlap at mid elevations where phylodiversities are most diverse, corresponding to a mid-domain effect at the phylogenetic scale. Drawing conclusions from phylodiversity to functional traits suggests an ecosystem with a high functional trait space along the gradient with a peak at mid-elevations. Altogether, the analysis of phylodiversity patterns revealed a much more complex picture of the diversity distribution than taxonomic diversity. Furthermore, phylodiversity permitted to find the evolutionary biotic and abiotic processes which shaped the diversity structure.