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

Resumen:

Purpose of the Review The escalating impacts of human activities and climate change, particularly increased nutrient leaching and deposition, could significantly alter the productivity, structure, and function of tropical vegetation. To better understand how nutrient deposition affects regeneration in tropical ecosystems, we synthesised studies that added N, P, NP, or NPK to the seedlings of tropical tree and shrub species. Recent Findings In the tropics, nutrient limitation leads to multiple resource constraints. Our systematic review and hierarchical meta-analyses aimed to: (1) test the effect of nutrient addition on the growth rate and biomass allocation of seedlings of tropical species; (2) examine seedling responses across climate-defined groups; (3) quantify the effects of experimental methods and wood density on species’ responses to experimental fertilisation. Summary Overall, nutrient addition increased seedling shoot biomass by 26% and growth rates by 14%. Pot and transplantation experiments demonstrated stronger positive effects than in-situ observational studies. Nutrient combinations yielded the highest growth rates (NPK: 27%, and NP: 18%), and N was critical for shoot biomass (N: 38%, and NP: 48%). The responses of shoot biomass indicated co-limitation of N and P, but also high variability in seedling responses to individual nutrients. Temperature and precipitation had indirect regulating effects, while seasonality showed the strongest impact in seasonally dry sites (38% growth rate and 70% shoot biomass). Species showed individual responses to nutrients, influenced by biotic and abiotic interactions. Finally, we suggest tracking additional parameters, like forest successional status, that may intensify nutrient deposition effects on tropical soils due to climate change.

Resumen:

Models of global climate change generally predict higher rainfall variability, with more intense rainfall events separated by extended dry periods. We experimentally studied the effects of prolonged droughts on diverse ant assemblages found at three elevations in an Ecuadorian montane rainforest. We hypothesized that most species will be negatively affected directly (physiological stress) or indirectly (less food or suitable nesting resources) by drought. We thus expected a decrease in species richness as well as changes in assemblage composition. As the decrease of moisture content was expected to be more marked above ground than in soil, its impact on ants should differ according to their nesting site (dead wood, leaf litter, soil). After 6-month treatments, dead wood, leaf litter and soil samples were on average 53%, 46% and 4% drier under tents than controls, respectively. The drought did not alter overall species richness in the three nesting situations. However, species composition was significantly modified, mostly in dead wood and in leaf litter. Camponotus in dead wood, Strumigenys in leaf litter and Solenopsis in all three microhabitats were more abundant under tents. In contrast, Pheidole in dead wood, and Pachycondyla in leaf litter, were less abundant than in controls. Similar trends were observed at the three study sites. To conclude, after 6-month droughts dominant ant genera in the assemblages were affected differently. In the longer term, alteration of the rainfall regime is therefore expected to have an important impact on ants, as well as on their ecosystem functions and services, through shifts in species dominance and composition. Zusammenfassung Die Modelle des globalen Klimawandels prognostizieren im Allgemeinen variablere Niederschläge mit intensiveren Regenfällen, denen ausgedehnte Trockenperioden folgen. Wir untersuchten experimentell die Auswirkungen von längeren Trockenphasen auf verschiedene Ameisengemeinschaften auf drei Höhenstufen im Bergregenwald von Ecuador. Wir stellten die Hypothese auf, dass Trockenheit sich auf die meisten Arten negativ auswirken würde, sei es direkt (physiologischer Stress) oder indirekt (weniger Futter oder geeignetes Nistmaterial). Wir erwarteten daher eine Abnahme des Artenreichtums sowie Veränderungen in der Zusammensetzung der Arten. Da zu erwarten war, dass die Abnahme der Feuchtigkeit über dem Boden deutlicher sein würde als im Boden, sollten die Auswirkungen auf Ameisen je nach Nistplatz (Totholz, Laub, Erdreich) verschieden sein. Nach sechsmonatiger Behandlung waren die Totholz-, Laub und Erdproben unter den Abdeck-Zelten jeweils durchschnittlich 53%, 46% und 4% trockener als an den Kontrollpunkten. Die Trockenheit hat den Artenreichtum insgesamt in den drei Nist-Situationen nicht verändert. Die Zusammensetzung der Arten hatte sich jedoch signifikant verändert, vor allem in Totholz und Laub. Camponotus in Totholz, Strumigenys in Laub und Solenopsis in allen drei Mikrohabitaten waren unter den Zelten häufiger. Andererseits waren Pheidole in Totholz sowie Pachycondyla in Laub weniger häufig als auf den Kontrollflächen. Ähnliche Tendenzen wurden an allen drei untersuchten Orten beobachtet. Zusammenfassend lässt sich sagen, dass die dominanten Ameisengattungen nach sechsmonatigen Trockenphasen unterschiedlich betroffen waren. Langfristig ist daher zu erwarten, dass eine Veränderung der Niederschlagsmuster durch Veränderungen in der Arten-Dominanz und –zusammensetzung wichtige Auswirkungen auf Ameisen hat, sowie auf ihre Funktionen und Dienste im Ökosystem.