Found 2 publication(s)
Pierick, K. (2017): Variation of tree fine root traits along a topographical gradient in an Ecuadorian tropical montane forest University of Goettingen, master thesis
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- Abstract: Although fine root trait...
- Keywords: | topographic heterogenity | fine roots | functional richness | functional traits |
Abstract:Although fine root traits are crucially important for plants and ecosystems, little is known about the mechanisms driving their variation. According to the theory of the plant economics spectrum, plants have to adopt a consistent strategy for all organs on a one-dimensional axis from slow to fast nutrient acquisition. The different strategies are supposed to be reflected in fine root traits, and to vary with resource availability. This master’s thesis aimed to investigate the variation of tree fine root traits along a topographical gradient in southern Ecuador, and their coordination with aboveground traits, in order to find evidence for a plant economics spectrum. In a tropical montane forest near Loja, fine root systems (diameter < 2 mm) of 179 adult trees were sampled from 18 plots at different slope positions. The steep slopes in this megadiverse ecosystem are characterized by decreasing fertility from the lower to the upper slope, and a high turnover of tree species on small scales along the slopes. The traits root diameter, specific root length (SRL), root tissue density (RTD), root branching intensity (RBI) and nitrogen content (N root ) were measured on each root system. The root traits were tested for being correlated with a topography index, edaphic factors, and aboveground traits. These relationships were analyzed both on the level of plot means and individual trees. Moreover, functional dispersion of the root traits was calculated for each plot and related to the topographical gradient. Pagel’s ? was calculated as an indicator of phylogenetic signal for each root trait. Furthermore, mixed effect models and principal component analyses were calculated in order to better understand the complex relationships between environment, plant traits, and phylogeny. Fine roots tended to be thicker and less intensely branched, contain less nitrogen and have lower SRL with increasing distance from the lower slope. Functional dispersion decreased from lower to upper slope. Especially SRL and N root were closely linked to aboveground traits. Trees with high SRL and N root tended to have softer wood and leaves, higher specific leaf area and higher leaf N and P concentrations. These trends were also apparent when comparing plot means instead of data from tree individuals. This indicates that trees evolved consistent resource economic strategies that manifest in their fine roots, wood, and leaves. Species with a slow, conservative strategy are typical for the upper slopes, whereas acquisitive species assembled at the lower slopes. However, RTD was independent from the topographical gradient and most aboveground traits. SRL, N root and root diameter had strong phylogenetic signals. Rubiaceae and Moraceae were typical families with acquisitive traits growing at the lower slope, whereas the early-diverged Lauraceae occurred predominantly at the upper slope and had very thick roots of the conservative type. These findings provide valuable new insights into patterns of fine root trait variation. They confirm the hypothesis of a plant economics spectrum where root traits are integrated, and demonstrate that tree species in tropical montane forests assemble along topographical gradients according to their resource economics strategies and the associated trait combinations.
Tiede, Y.; Schlautmann, J.; Donoso, D.A.; Wallis, C.; Bendix, J.; Brandl, R. & Farwig, N. (2017): Ants as indicators of environmental change and ecosystem processes. Ecological indicators 1(1), 1-6.
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- DOI: 10.1016/j.ecolind.2017.01.029
- Abstract: Environmental stressors ...
- Keywords: | elevational gradient | species traits | forest degradation | path model | artificial caterpillars | functional richness |
Abstract:Environmental stressors and changes in land use have led to rapid and dramatic species losses. As such, we need effective monitoring programs that alert us not only to biodiversity losses, but also to functional changes in species assemblages and associated ecosystem processes. Ants are important components of terrestrial food webs and a key group in food web interactions and numerous ecosystem processes. Their sensitive and rapid response to environmental changes suggests that they are a suitable indicator group for the monitoring of abiotic, biotic, and functional changes. We tested the suitability of the incidence (i.e. the sum of all species occurrences at 30 baits), species richness, and functional richness of ants as indicators of ecological responses to environmental change, forest degradation, and of the ecosystem process predation on herbivorous arthropods. We sampled data along an elevational gradient (1000–3000 m a.s.l.) and across seasons (wetter and drier period) in a montane rainforest in southern Ecuador. The incidence of ants declined with increasing elevation but did not change with forest degradation. Ant incidence was higher during the drier season. Species richness was highly correlated with incidence and showed comparable results. Functional richness also declined with increasing elevation and did not change with forest degradation. However, a null-model comparison revealed that the functional richness pattern did not differ from a pattern expected for ant assemblages with randomly distributed sets of traits across species. Predation on artificial caterpillars decreased along the elevational gradient; the pattern was not driven by elevation itself, but by ant incidence (or inter-changeable by ant richness), which positively affected predation. In spite of lower ant incidence (or ant richness), predation was higher during the wetter season and did not change with forest degradation and ant functional richness. We used path analysis to disentangle the causal relationships of the environmental factors temperature (with elevation as a proxy), season, and habitat degradation with the incidence and functional richness of ants, and their consequences for predation. Our results would suggest that the forecasted global warming might support more active and species-rich ant assemblages, which in turn would mediate increased predation on herbivorous arthropods. However, this prediction should be made with reservation, as it assumes that the dispersal of ants keeps pace with the climatic changes as well as a one-dimensional relationship between ants and predation within a food-web that comprises species interactions of much higher complexity. Our results also suggested that degraded forests in our study area might provide suitable habitat for epigaeic, ground-dwelling ant assemblages that do not differ in incidence, species richness, functional richness, composition, or predation on arthropods from assemblages of primary forests. Most importantly, our results suggest that the occurrence and activity of ants are important drivers of ecosystem processes and that changes in the incidence and richness of ants can be used as effective indicators of responses to temperature changes and of predation within mega-diverse forest ecosystems.