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

Abstract:

The co-evolutionary arms race between herbivores and plants forces plants to evolve protection strategies that reduce the palatability of the plant modules attacked by the herbivores. These characteristics of traits have consequences for both the survival of plant individuals and the composition of plant communities. Thus, correlating traits of for instance leaves with herbivory is an important step toward understanding the dynamics of plant populations and communities. Traits can either be measured using conventional lab methods or recently developed spectral sensing techniques. We examined whether leaf traits of trees are related to herbivory in a multispecies approach. Furthermore, we explored whether leaf traits characterized by spectral sensing provide similar relations to herbivory as lab-based leaf traits. We established nine 1-ha square plots evenly distributed over three different forest types in Ecuadorian tropical montane rainforests where we estimated herbivory as the leaf area loss (in square centimeters) of 20 (±5) leaves sampled from the canopies of 380 tree individuals belonging to 51 tree species (7 ± 1 individuals/species) using lab- and spectral-sensing-based methods. For each methodological approach, we ran 100 linear mixed-effects models with all respective leaf traits as predictor and herbivory as response variables for data subsets containing one randomly selected tree individual of each species to estimate the range of the regression coefficients for each trait. Automated stepwise backward selections determined the frequency of each trait having an important influence on herbivory. We found no clear relations between leaf traits and herbivory for neither lab- nor spectral-sensing-based traits. A nested variance component analysis demonstrated that the observed variability was mainly due to the variation in trait concentrations between tree individuals of a species. Our results suggest that snapshot data lead to a mismatch between herbivory and the concentrations of traits during the peak of herbivory. Another explanation could be that environmental conditions or processes along the food web are more important in structuring herbivory than leaf traits.

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:

In tropical regions insect herbivores are considered one of the key players in the ecosystem function by effecting the nutrient cycle as well as the carbon sequestration of these systems. However, their feeding is strongly influenced by abiotic factors, like temperature, leading to a lower performance and abundance of herbivores under lower temperature, as well as biotic factors, like plant defence mechanisms (e.g. tougher leaves or a higher concentration of secondary metabolites). But plants are facing a constant trade-off between growth and defence, which is stronger under harsher environmental conditions. The resulting differences in defence further lead to a big variability in the rate of herbivory between the plants. Although several studies investigated the interaction between herbivory, biotic and abiotic factors, most of them concentrate on single species and systems. However, since herbivory varies between species and has high impacts on the whole ecosystem by influencing plants viability and the carbon sequestration, it is crucial to investigate the interaction on community level. We therefore assessed herbivory across an elevational gradient of 1000 m to 3000 m a.s.l. on a community level, i.e. by measuring 313 representative tree species. To determine the biotic interaction we measured leaf traits using both conventional and remote sensing methods, to look for the applicability of remote sensing for extrapolation of community patterns. Our study shows, that herbivory decreased with increasing elevation. Furthermore, sulphur showed a positive association with herbivory and SLA, nitrogen and tannin showed a negative association. The influence of carotenoid on herbivory changed from a positive to a negative one with elevation and anthocyanin showed the opposite pattern. Phylogeny thereby had the same effect on both conventional and remote sensing measured leaf traits. Our results showed, that the influence of the abiotic factors especially at higher elevations were strong, leading to the conclusion, that community level herbivory is more effected by the abiotic interaction along the elevational gradient than the biotic interaction. Moreover, the models of conventionally and remote sensing determined leaf traits had a strong congruence regarding the influence of abiotic and biotic factors on herbivory, although they comprise different leaf traits. Consequently we can state, that remote sensing can be used to predict herbivory on a community level in a tropical mountain forest.

Abstract:

The anthropogenic deposition of nitrogen (N) and phosphorus (P) into terrestrial ecosystems has an influence on the leaf morphology and leaf properties of vegetation as well as on interactions within an ecosystem. In this context, the increased availability of nutrients has an impact on herbivory. In addition to the availability of nutrients, sea level has also been shown to influence these parameters. The shown work deals with the quantification of herbivory under the influence of N- and P-fertilization and differences in certain leaf parameters (leaf area, specific leaf area, leaf toughness, leaf nitrogen content and leaf area loss) between three altitudinal levels (1000 m, 2000 m, 3000 m). The study area was located in a tropical mountain rainforest in Southern Ecuador. In a nutrient manipulation experiment (NUMEX) 48 plots within the study areas were fertilized with either N, P or NP twice a year. Per plot 50 leaves were collected, examined for various parameters and then subjected to a nutrient analysis. The aim of this study was to figure out to what extent sea level influences the leaf morphology, nitrogen content and the leaf area loss of the vegetation within the control areas and to what extent fertilization with nitrogen, phosphorus or both elements changes these leaf properties. Finally, it was investigated whether possible changes in feeding rates resulted from an increased leaf nitrogen content. Sea level had a major influence on leaf strength, which increased with increasing height gradients, and on the specific leaf area and the mean leaf area, which decreased with increasing sea level. Many of the values differed significantly between the altitudinal levels. This suggests that not only the soil becomes nutrient-poorer with rising sea level, but also that the mineralisation of the few available nutrients is slower than at lower altitudes. The climatic environmental conditions, which become more extreme as the sea level rises, also explain the changes in the leaf parameters mentioned. Fertilisation instead did not have an influence as strong as sea level on the studied parameters. There were hardly any significant differences between the plots with different fertilisation. Since tropical forests are considered nutrient-limited, the addition of nitrogen led to the formation of large and soft leaves, which was expected. The correlations between leaf nitrogen content and SLA or leaf strength were positive and significant. Leaf area loss did not correlate with nitrogen content, which was unexpected. This can be attributed to the fact that plants show highly species-specific reactions to nutrient availability, which manifest themselves in very different plastic changes in growth and defence mechanisms against herbivore species. In this work a strong influence of the sea level on the leaf parameters could be determined. An increasing influence of fertilization on the feeding rate of herbivorous species was not found.

Abstract:

The tropical Andes are one of the most biodiverse hotspots on earth. Though the nutrient-limited systems are affected by anthropogenic nutrient inputs due to industry and agriculture. The NuMEx (Nutrient Manipulation Experiment) project, which was set up in 2008 and is located in southern Ecuador and aims to find out about the consequences of nutrient pollution to herbivore and plant interaction. Therefore experimental plots at three different levels of elevation were fertilised with nitrogen and phosphorus. In this study, fresh leaf samples were collected in May 2018. Plant parameters like leaf area, specific leaf area, leaf toughness and nitrogen content were analysed. Herbivory was examined trough leaf area loss measurements. Changes in these parameters along an elevation gradient from 1000 to 3000 m were analysed. Moreover, the study focussed on the influence of the nutrient addition to the sensible tropical system. A significant influence of the elevation on most of the leaf morphology parameters was shown. Specific leaf area and leaf nitrogen content showed a significant decrease along the elevation gradient, while the leaves became tougher. The mean leaf area and the leaf area loss gained no significant results; however, the leaf area tended to be smaller within rising elevation. The leaf area loss was highest at 3000 m of elevation. All elevation outcomes, except for the leaf area loss, could be explained by the harsher climatic conditions at higher elevation levels and the relationship between nitrogen content and the leaf traits. Nutrient addition results on the leaf traits were less clear. Almost no significant influences could be measured. The leaf characteristics showed mostly a clear trend though, except for the leaf area. The leaf area partially increased (mostly under mixed nitrogen and phosphorus addition) and partially decreased (nitrogen treatment) due to the nutrient addition. Specific leaf area, leaf nitrogen content and leaf area loss mostly increased due to the nutrient addition, especially nitrogen and the mixed nitrogen and phosphorus sample contributed to the increase. Leaf toughness whereas decreased. The highest decrease was caused at the plots treated with the nitrogen and phosphorus mix. The results make clear that a high leaf nitrogen content correlates with soft leaves and a high specific leaf area. An analysis of the leaf area loss and the leaf nitrogen content yielded that also these traits are correlated.

Abstract:

Tropical montane forests of the Andes belong to the hotspots of biodiversity. But these nutrient poor ecosystems are simultaneously threatened by increased element inputs of nitrogen and phosphor in nutrient cycles. NUMEX-Projekt simulates the expected nutrient inputs in the for-ests and quantifies the changes of this ecosystem. In line of this study litter samples were collected by littertraps during a working period from February till May 2016. Leaf litter produc-tion, parameters of leaf morphology (leaf area and specific leaf area) and litter nutrients of nitrogen and phosphor were determined. Additionally, the parameters of herbivory (leaf mass loss and leaf area loss) were calculated by measuring holes area. The variation of these pa-rameters along an altitudinal gradient from 1.000 m.a.s.l. to 3.000 m.a.s.l. was investigated. Besides the variation after nitrogen and/or phosphor addition was explored. Furthermore, the extend of nutrients, lost through herbivory, was identified for the stand level. Terminatory the influence of two soil parameters (C/N ratio and Presin) was discussed. There is a significant influence of altitude (p<0,05) on leaf morphology (leaf area: 1.000 m.a.s.l: 26,4±1,6 cm², 3.000 m.a.s.l: 7,4±1,0 cm², specific leaf area: 1.000 m.a.s.l: 99,7±4,1 cm²·g-1, 3.000 m.a.s.l: 56,1±6,6 cm²·g-1), leaf nutrients of nitrogen (1.000 m.a.s.l: 15,3±0,5 g·kg-1, 3.000 m.a.s.l: 6,6±0,7 g·kg-1) and phosphor (1.000 m.a.s.l: 0,54±0,03 g·kg-1, 3.000 m.a.s.l: 0,25±0,03 g·kg-1) and also on the parameters of herbivory: holes area (1.000 m.a.s.l: 1,8±0,2 cm², 3.000 m.a.s.l: 0,3±0,1 cm²) and leaf area loss (1.000 m.a.s.l: 6,8±0,4 %, 3.000 m.a.s.l: 3,6±0,6 %). Nutrient addition did not lead to distinct results according to the variation of measured param-eters. NP fertilization had a positive effect on leaf area and P fertilization a positive effect on specific leaf area. Leaf nutrients showed various answers. For this parameter, NP fertilization causes significantly raised nitrogen and phosphor concentrations in litter in each site. Leaf litter production in 1.000 m.a.s.l site significantly decreased through NP fertilization. Referring to herbivory only a little number of significant effects were detected. Holes area increased on 2.000 m.a.s.l site by NP addition while leaf area loss in 1.000 m.a.s.l site – as well as leaf area production – decreased. On stand level, there was no variation of leaf area loss. Soil parameters have a higher impact on measured parameters on stand level. Specific leaf area and leaf area loss correlate positively with soil C/N of upper mineral soil. Correlations of these parameters with plant available phosphor Presin is negative. Nutrient losses on stand level decrease with altitude. There was a negative effect of NP addition on nitrogen loss in 1.000 m.a.s.l site and a positive effect of NP addition on phosphor loss in all sites.

Abstract:

The worldwide demand for large scale biodiversity monitoring systems is challenging for recent remote sensing techniques. For monitoring changes in species as well as functional diversity the consideration of ecosystem processes is crucial. Herbivory as a focal function in tropical forest ecosystems is therefore being investigated in this study. Aim of the study is to reveal the potential of remotely sensed image textures for predicting herbivory. For this leaf area loss (LAL) due to herbivory has been quantified in different vegetation layers of a tropical mountain forest in the Ecuadorian Andes. The study area is a structurally highly complex region along an elevation gradient from 1000 to 3000 m a.s.l. with undisturbed primary forest and disturbed forest fragments within agriculturally used land. It has been proven that LAL has similar patterns as herbivore abundance over the elevation gradient showing it to be a possible proxy for herbivore abundance. Further results show a correlation of LAL data and canopy cover thus local forest structure. Correlations between LAL and image textures as a proxy for vegetation structure were stronger than with pixel wise derived spectral values only. Unveiling the high potential of image textures as a surrogate for herbivory and ecosystem function.

Abstract:

Nitrogen deposition to tropical forests is predicted to increase in future in many regions due to agricultural intensification. We conducted a seedling transplantation experiment in a tropical premontane forest in Ecuador with a locally abundant late-successional tree species (Pouteria torta, Sapotaceae) aimed at detecting species-specific responses to moderate N and P addition and to understand how increasing nutrient availability will affect regeneration. From locally collected seeds, 320 seedlings were produced and transplanted to the plots of the Ecuadorian Nutrient Manipulation Experiment (NUMEX) with three treatments (moderate N addition: 50 kg N ha?1 year?1, moderate P addition: 10 kg P ha?1 year?1 and combined N and P addition) and a control (80 plants per treatment). After 12 months, mortality, relative growth rate, leaf nutrient content and leaf herbivory rate were measured. N and NP addition significantly increased the mortality rate (70 vs. 54% in the control). However, N and P addition also increased the diameter growth rate of the surviving seedlings. N and P addition did not alter foliar nutrient concentrations and leaf N:P ratio, but N addition decreased the leaf C:N ratio and increased SLA. P addition (but not N addition) resulted in higher leaf area loss to herbivore consumption and also shifted carbon allocation to root growth. This fertilization experiment with a common rainforest tree species conducted in old-growth forest shows that already moderate doses of added N and P are affecting seedling performance which most likely will have consequences for the competitive strength in the understory and the recruitment success of P. torta. Simultaneous increases in growth, herbivory and mortality rates make it difficult to assess the species' overall performance and predict how a future increase in nutrient deposition will alter the abundance of this species in the Andean tropical montane forests.