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

Abstract:

Decomposition is a very important process. It is supporting nutrient cycles and for that reason crucial for the functionality of ecosystems. Various studies have shown that decomposition is driven by abiotic and biotic factors such as climate, seasonal weather conditions (like el Niño), soil organisms and disturbance of forests. In this study, the focus lies on investigating the impact of abiotic factors on the decomposition with a new simplified and standardised method, with tea bags as litterbags. Green tea bags were buried in two years, on different elevations between 1000 m a.s.l. and 3000 m a.s.l. in 500 m steps on disturbed and undisturbed plots in the Ecuadorian Andes. After 21 days in the soil, the decomposition rate were calculated and compared on different elevations and different disturbances in two different years. The disturbance had no effect, because the disturbed plots were fragmented and the study took place in the interior of these fragments; here no edge effects influenced the decomposition rate. As expected, the decomposition rate declined with an increase in elevation, due to changing climate conditions. In the lower, wet and warm elevations, it was faster than in the higher elevation where the climate is wetter but also colder. In the test series from 2015, the decomposition rate was higher in the upper elevations than in 2014, this could be explained by a weather phenomenon called el Niño, which took place in 2015. It leads to a slightly higher temperature and 60% more precipitation than what normally would be expected in 2015. These differences between the two years show the importance of taking seasonal and annual variations into account while investigating decomposition and the sensitivity of this important ecosystem process to changing weather and climate conditions.

Abstract:

Climate change and forest degradation are major threats to forest ecosystems. The climatic changes can affect the mineralization rate in soils and therefore change the amount of available nitrogen components for plants. Thus these changes can influence foliar C/N-ratio. Previous studies used an elevation gradient to test the influence of climatic changes on ecosystems, and showed that foliar C/N-ratio is positively correlated with elevation. Changes in foliar C/N-ratio may affect the feeding behavior of insect herbivores and therefore influence leaf area loss (LAL). LAL is used as an indicator of herbivory and therefore may consequently also be related to ant abundance because ants prey on insect herbivores. Ants in return, are also affected by the abiotic changes with increasing elevation and therefore sensitive to climate change. However, forest degradation is currently the greater threat to ecosystems. Degradation can lead to changes in the nutrient uptake of plants and therefore to changes in foliar C/N-ratio. Moreover it can reduce ant abundance as ants are sensitive to the conversion of forests. We nalyzed the causal effects of abiotic factors (elevation and degradation) on biotic factors (foliar C/N-ratio and ant activityabundance) and the relationships between the biotic factors and LAL with linear mixed-effect models in a path model. We found a significant positive correlation between foliar C/N-ratio and elevation, and a significant negative correlation between ant activity-abundance and elevation. Foliar carbon-content had a significant negative correlation with degradation. Our results revealed no significant relationships with LAL, but LAL correlated negatively with foliar C/N-ratio in the shrub layer. The results of our study point out that foliar C/N-ratio and ant activityabundance change with elevation and thus respond to climatic changes. Moreover our results indicate that foliar C/N-ratio can be connected to LAL, but that influences such as the abundance and distribution of insect herbivores along elevation should be examined closely. Our finding that foliar C/N-ratio, ant activity-abundance and LAL were unaffected by degradation indicates that the studied degraded forests are still suitable habitats for insect herbivores and ants.

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.