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

Abstract:

Herbivory is an important plant-animal interaction which impacts ecosystems in various ways, e.g., influencing nutrient cycles, plant productivity, and community composition. Herbivory therefore plays a crucial role in maintaining ecosystem functions of tropical rainforests. As plants are negatively impacted by herbivory, they have developed antiherbivore defense strategies, which reduce herbivory levels. Additionally, herbivory is known to decrease under harsh climatic conditions, because herbivorous arthropods are impacted by temperature and precipitation. However, it has yet to be clarified whether herbivory is primarily impacted directly by climatic (i.e., abiotic) factors or indirectly through plant traits (i.e., biotic factors). In this study we investigated the influence of temperature, precipitation, and various leaf traits, like specific leaf area (SLA) and nutrient concentration, on herbivory along an elevational gradient from 1000 to 3000 m a.s.l. in a tropical rainforest in South Ecuador. We found lower herbivory levels at higher elevation in response to decreased temperature and SLA. Moreover, herbivory levels decreased with precipitation. Hence, we demonstrated that climate has a significant direct and indirect impact on tropical ecosystems by influencing herbivory.

Abstract:

Questions: How does the structure of liana communities (diameter, density and biomass) in tropical montane forests vary along elevation and topographic gradients? How do patterns of tree infestation vary with elevation? Is tree diameter growth reduced by lianas in tropicalmontane forest? Location: Tropical Andean forests (1000–3000 m a.s.l.) in the San Francisco Reserve and in the Podocarpus National Park, southern Ecuador. Methods: All lianas (DBH ? 1 cm) were censused in 54 permanent plots (20 9 20 m) equally distributed between three study sites (1000, 2000 and 3000 m a.s.l.) and three topographic positions (lower, mid and upper slope) per site (six replicate plots at each site by position combination). The DBH and number of lianas hosted was recorded for all trees (DBH ? 10 cm). Liana biomass was estimated using allometric equations. ANOVAs were used to test for effects of elevation and slope positions on liana parameters and proportion of trees infested. The relationships between liana biomass and tree parameters and environmental parameters were analysed with partial least squares regression. We used the available literature data to perform a regression analysis of liana biomass in response to elevation in humid tropical old-growth forests between sea level and 3000 ma.s.l. Results: Liana diameter, density and biomass all decrease with elevation. The decreasing liana biomass agrees with results from previous studies of liana biomass in other humid tropical forests, indicating a decrease of 0.18 Mg/ha liana biomass per 100 m of elevation gain. Topographic variation leads to thinner but more abundant stems upslope; there was no effect of topographic position on liana biomass. Liana biomass and liana infestation are both positively correlated with host tree DBH at every elevation. Tree diameter growth is reduced by liana infestation; the proportion of infested trees is lower in Andean montane forests than in tropical lowland forests. Conclusions: Liana biomass distribution and tree infestation vary significantly with elevation. Biomass of lianas and relative contribution of lianas to total above-ground biomass both decrease with elevation. Topographic effects likely result fromhigher soil fertility at lower slope positions.

Abstract:

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.

Abstract:

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.