Recent studies link increased ozone (O3) and carbon dioxide (CO2) levels to alteration of plant performance and plant-herbivore interactions, but their interactive effects on plant-pollinator ...interactions are little understood. Extra floral nectaries (EFNs) are essential organs used by some plants for stimulating defense against herbivory and for the attraction of insect pollinators, e.g., bees. The factors driving the interactions between bees and plants regarding the visitation of bees to EFNs are poorly understood, especially in the face of global change driven by greenhouse gases. Here, we experimentally tested whether elevated levels of O3 and CO2 individually and interactively alter the emission of Volatile Organic Compound (VOC) profiles in the field bean plant (Vicia faba, L., Fabaceae), EFN nectar production and EFN visitation by the European orchard bee (Osmia cornuta, Latreille, Megachilidae). Our results showed that O3 alone had significant negative effects on the blends of VOCs emitted while the treatment with elevated CO2 alone did not differ from the control. Furthermore, as with O3 alone, the mixture of O3 and CO2 also had a significant difference in the VOCs' profile. O3 exposure was also linked to reduced nectar volume and had a negative impact on EFN visitation by bees. Increased CO2 level, on the other hand, had a positive impact on bee visits. Our results add to the knowledge of the interactive effects of O3 and CO2 on plant volatiles emitted by Vicia faba and bee responses. As greenhouse gas levels continue to rise globally, it is important to take these findings into consideration to better prepare for changes in plant-insect interactions.
Aim: Identifying traits that enhance the success of animals in unhospitable climates helps to understand biogeographical patterns and to predict the consequences of climatic changes. On temperate ...mountains, traits that increase cold performance potentially allow species to colonize higher elevations. We first tested the importance of morphological traits for the cold performance of bees. Second, we assessed the relevance of these traits for species distributional patterns by analysing intraspecific and interspecific trait shifts along elevational gradients. Location: National Park Berchtesgaden, Germany; Würzburg, Germany. Methods: We determined thermal activity thresholds by measuring signs of immobility along temperature gradients under laboratory conditions and related them to morphometric traits. We sampled bee communities at 34 sites along an elevation gradient in the northern Alps, measured for all species morphometric traits and thermal activity limits in the field, and analysed how trait measures changed with elevation within and across species. Results: Laboratory and field experiments revealed that bees with larger body size, longer hair and relatively short wings tolerated lower temperatures before reaching immobility and started being active in the field at lower temperatures than small, short-haired and long-winged species. In correspondence to these results, we found that morphometric traits increased (body size, hair length) or decreased (relative wing length) with increasing elevation in communities and, in case of body size, also within species. Main conclusions: Results of laboratory and field experiments and their reflectance in community- and species-level trends of morphological traits along elevational gradients underscore the adaptive nature of large body size, long hair and short wings for bees' thermal performance. Morphological traits expanding lower thermal limits probably contribute to the fitness of bees in cold environments and may simultaneously be under selection in a warming world.
Agriculture and the exploitation of natural resources have transformed tropical mountain ecosystems across the world, and the consequences of these transformations for biodiversity and ecosystem ...functioning are largely unknown
. Conclusions that are derived from studies in non-mountainous areas are not suitable for predicting the effects of land-use changes on tropical mountains because the climatic environment rapidly changes with elevation, which may mitigate or amplify the effects of land use
. It is of key importance to understand how the interplay of climate and land use constrains biodiversity and ecosystem functions to determine the consequences of global change for mountain ecosystems. Here we show that the interacting effects of climate and land use reshape elevational trends in biodiversity and ecosystem functions on Africa's largest mountain, Mount Kilimanjaro (Tanzania). We find that increasing land-use intensity causes larger losses of plant and animal species richness in the arid lowlands than in humid submontane and montane zones. Increases in land-use intensity are associated with significant changes in the composition of plant, animal and microorganism communities; stronger modifications of plant and animal communities occur in arid and humid ecosystems, respectively. Temperature, precipitation and land use jointly modulate soil properties, nutrient turnover, greenhouse gas emissions, plant biomass and productivity, as well as animal interactions. Our data suggest that the response of ecosystem functions to land-use intensity depends strongly on climate; more-severe changes in ecosystem functioning occur in the arid lowlands and the cold montane zone. Interactions between climate and land use explained-on average-54% of the variation in species richness, species composition and ecosystem functions, whereas only 30% of variation was related to single drivers. Our study reveals that climate can modulate the effects of land use on biodiversity and ecosystem functioning, and points to a lowered resistance of ecosystems in climatically challenging environments to ongoing land-use changes in tropical mountainous regions.
Species' functional traits set the blueprint for pair-wise interactions in ecological networks. Yet, it is unknown to what extent the functional diversity of plant and animal communities controls ...network assembly along environmental gradients in real-world ecosystems. Here we address this question with a unique dataset of mutualistic bird-fruit, bird-flower and insect-flower interaction networks and associated functional traits of 200 plant and 282 animal species sampled along broad climate and land-use gradients on Mt. Kilimanjaro. We show that plant functional diversity is mainly limited by precipitation, while animal functional diversity is primarily limited by temperature. Furthermore, shifts in plant and animal functional diversity along the elevational gradient control the niche breadth and partitioning of the respective other trophic level. These findings reveal that climatic constraints on the functional diversity of either plants or animals determine the relative importance of bottom-up and top-down control in plant-animal interaction networks.
The factors determining gradients of biodiversity are a fundamental yet unresolved topic in ecology. While diversity gradients have been analysed for numerous single taxa, progress towards general ...explanatory models has been hampered by limitations in the phylogenetic coverage of past studies. By parallel sampling of 25 major plant and animal taxa along a 3.7 km elevational gradient on Mt. Kilimanjaro, we quantify cross-taxon consensus in diversity gradients and evaluate predictors of diversity from single taxa to a multi-taxa community level. While single taxa show complex distribution patterns and respond to different environmental factors, scaling up diversity to the community level leads to an unambiguous support for temperature as the main predictor of species richness in both plants and animals. Our findings illuminate the influence of taxonomic coverage for models of diversity gradients and point to the importance of temperature for diversification and species coexistence in plant and animal communities.
Urogenital schistosomiasis (UGS) caused by Schistosoma haematobium is endemic in the South West Region of Cameroon. An understanding of the abundance and distribution of the Bulinus snail, ...intermediate host can inform strategic snail control programmes at a local scale. This study investigated seasonal dynamics and environmental factors influencing occurrence and abundance of freshwater snail intermediate hosts in Tiko, a semi-urban endemic focus in the Mount Cameroon area. A longitudinal malacological field survey was conducted between December 2019 and December 2020 in the Tiko municipality. Snails were collected for one year monthly at 12 different human water contact sites along a stretch of the Ndongo stream using a standardized sampling technique. Freshwater snails were identified using shell morphological features. In addition, water temperature, pH, electrical conductivity, total dissolved solutes, salinity, water depth, width and flow velocity were measured, and vegetation cover as well as substrate type were determined. Bayesian regression models were used to identify the main environmental factors affecting the occurrence and abundance of Bulinus intermediate host. In total, 2129 fresh water snails were collected during the study period. Physa (51.4%) was the most abundant genus followed by Melanoides (28.6%) then, Bulinus (15.5%), Lymnaea (4.2%), Indoplanorbis (0.2%) and Potadoma (0.1%). Seasonality in abundance was significant in Bulinus sp as well as other genera, with greater numbers in the dry season (peaks between December and February). Water temperature, a rocky or sandy substrate type associated positively with Bulinus sp, meanwhile a higher water flow rate and medium vegetation negatively influenced the snail intermediate host population. These findings underscore the importance of timing behavioural and snail control interventions against schistosomiasis as well as increase vigilance of other trematode diseases in the study area. The continuous spread of planorbid snail hosts is a major concern.
Aim
Temperature, food resources and top‐down regulation by antagonists are considered as major drivers of insect diversity, but their relative importance is poorly understood. Here, we used ...cavity‐nesting communities of bees, wasps and their antagonists to reveal the role of temperature, food resources, parasitism rate and land use as drivers of species richness at different trophic levels along a broad elevational gradient.
Location
Mt. Kilimanjaro, Tanzania.
Taxon
Cavity‐nesting Hymenoptera (Hymenoptera: Apidae, Colletidae, Megachilidae, Crabronidae, Sphecidae, Pompilidae, Vespidae).
Methods
We established trap nests on 25 study sites that were distributed over similar large distances in terms of elevation along an elevational gradient from 866 to 1788 m a.s.l., including both natural and disturbed habitats. We quantified species richness and abundance of bees, wasps and antagonists, parasitism rates and flower or arthropod food resources. Data were analysed with generalized linear models within a multi‐model inference framework.
Results
Elevational species richness patterns changed with trophic level from monotonically declining richness of bees to increasingly humped‐shaped patterns for caterpillar‐hunting wasps, spider‐hunting wasps and antagonists. Parasitism rates generally declined with elevation but were higher for wasps than for bees. Temperature was the most important predictor of both bee and wasp host richness patterns. Antagonist richness patterns were also well predicted by temperature, but in contrast to host richness patterns, additionally by resource abundance and diversity. The conversion of natural habitats through anthropogenic land use, which included biomass removal, agricultural inputs, vegetation structure and percentage of surrounding agricultural habitats, had no significant effects on bee and wasp communities.
Main conclusions
Our study underpins the importance of temperature as a main driver of diversity gradients in ectothermic organisms and reveals the increasingly important role of food resources at higher trophic levels. Higher parasitism rates at higher trophic levels and at higher temperatures indicated that the relative importance of bottom‐up and top‐down drivers of species richness change across trophic levels and may respond differently to future climate change.
The mechanisms by which climatic changes influence ecosystem functions, that is, by a direct climatic control of ecosystem processes or by modifying richness and trait compositions of species ...communities, remain unresolved.
This study is a contribution to this discourse by elucidating the linkages between climate, land use, biodiversity, body size and ecosystem functions.
We disentangled direct climatic from biodiversity‐mediated effects by using dung removal by dung beetles as a model system and by combining correlative field data and exclosure experiments along an extensive elevational gradient on Mt. Kilimanjaro, Tanzania.
Dung removal declined with increasing elevation, being associated with a strong reduction in the richness and body size traits of dung beetle communities. Climate influenced dung removal rates by modifying biodiversity rather than by direct effects. The biodiversity–ecosystem effect was driven by a change in the mean body size of dung beetles. Dung removal rates were strongly reduced when large dung beetles were experimentally excluded.
This study underscores that climate influences ecosystem functions mainly by modifying biodiversity and underpins the important role of body size for dung removal.
Abstrakt
Die Mechanismen, durch die Klimaveränderungen die Funktionen von Ökosystemen beeinflussen, d.h. entweder durch einen direkten Einfluss des Klimas auf Ökosystemfunktionen oder durch indirekte klimatische Effekte auf die Biodiversität und Merkmalszusammensetzung von Artengemeinschaften, sind noch nicht geklärt.
Die vorliegende Studie leistet einen Beitrag zu diesem Diskurs, indem sie die Zusammenhänge zwischen Klima, Landnutzung, Artenvielfalt, Körpergröße und Ökosystemfunktionen untersucht.
Um direkte Klimaeffekte von Biodiversitätseffekten zu unterscheiden, verwendeten wir das Modellsystem Dungabbau durch Dungkäfer. Wir kombinierten korrelative Felddaten und Experimente entlang eines ausgedehnten Höhengradienten auf dem Kilimandscharo in Tansania.
Der Dungabbau nahm mit zunehmender Höhe ab, was mit einer starken Verringerung der Diversität und der Körpergröße der Dungkäfergemeinschaften einherging. Das Klima beeinflusste den Dungabbau indirekt über die Artenvielfalt und nicht durch direkte Effekte. Verantwortlich für den Biodiversitäts‐Ökosystem‐Effekt war die Körpergröße der Dungkäfer. Der Dungabbau war stark reduziert, wenn große Dungkäfer experimentell ausgeschlossen wurden.
Diese Studie unterstreicht, dass das Klima vor allem indirekt über die Artenvielfalt auf Ökosystemfunktionen einwirkt und hebt die wichtige Rolle der Körpergröße der Dungkäfer für den Dungabbau hervor.
Currently, there is no consensus about the relative importance of climate, species richness, abundance and functional traits as drivers of ecosystem services. This study contributes to this discourse and disentangles the effects of temperature, precipitation, richness, body size and land use on dung removal, a central ecosystem service.
Aim
While elevational gradients in species richness constitute some of the best depicted patterns in ecology, there is a large uncertainty concerning the role of food resource availability for the ...establishment of diversity gradients in insects. Here, we analysed the importance of climate, area, land use and food resources for determining diversity gradients of dung beetles along extensive elevation and land use gradients on Mt. Kilimanjaro, Tanzania.
Location
Mt. Kilimanjaro, Tanzania.
Taxon
Scarabaeidae (Coleoptera).
Methods
Dung beetles were recorded with baited pitfall traps at 66 study plots along a 3.6 km elevational gradient. In order to quantify food resources for the dung beetle community in form of mammal defecation rates, we assessed mammalian diversity and biomass with camera traps. Using a multi‐model inference framework and path analysis, we tested the direct and indirect links between climate, area, land use and mammal defecation rates on the species richness and abundance of dung beetles.
Results
We found that the species richness of dung beetles declined exponentially with increasing elevation. Human land use diminished the species richness of functional groups exhibiting complex behaviour but did not have a significant influence on total species richness. Path analysis suggested that climate, in particular temperature and to a lesser degree precipitation, were the most important predictors of dung beetle species richness while mammal defecation rate was not supported as a predictor variable.
Main conclusions
Along broad climatic gradients, dung beetle diversity is mainly limited by climatic factors rather than by food resources. Our study points to a predominant role of temperature‐driven processes for the maintenance and origination of species diversity of ectothermic organisms, which will consequently be subject to ongoing climatic changes.
Aim
Species differ in their degree of specialization when interacting with other species, with significant consequences for the function and robustness of ecosystems. In order to better estimate such ...consequences, we need to improve our understanding of the spatial patterns and drivers of specialization in interaction networks.
Methods
Here, we used the extensive environmental gradient of Mt. Kilimanjaro (Tanzania, East Africa) to study patterns and drivers of specialization, and robustness of plant–pollinator interactions against simulated species extinction with standardized sampling methods. We studied specialization, network robustness and other network indices of 67 quantitative plant–pollinator networks consisting of 268 observational hours and 4,380 plant–pollinator interactions along a 3.4 km elevational gradient. Using path analysis, we tested whether resource availability, pollinator richness, visitation rates, temperature, and/or area explain average specialization in pollinator communities. We further linked pollinator specialization to different pollinator taxa, and species traits, that is, proboscis length, body size, and species elevational ranges.
Results
We found that specialization decreased with increasing elevation at different levels of biological organization. Among all variables, mean annual temperature was the best predictor of average specialization in pollinator communities. Specialization differed between pollinator taxa, but was not related to pollinator traits. Network robustness against simulated species extinctions of both plants and pollinators was lowest in the most specialized interaction networks, that is, in the lowlands.
Conclusions
Our study uncovers patterns in plant–pollinator specialization along elevational gradients. Mean annual temperature was closely linked to pollinator specialization. Energetic constraints, caused by short activity timeframes in cold highlands, may force ectothermic species to broaden their dietary spectrum. Alternatively or in addition, accelerated evolutionary rates might facilitate the establishment of specialization under warm climates. Despite the mechanisms behind the patterns have yet to be fully resolved, our data suggest that temperature shifts in the course of climate change may destabilize pollination networks by affecting network architecture.
We studied specialization patterns in plant–pollinator interactions along a 3.4 km elevational gradient on Mt. Kilimanjaro (Tanzania) and demonstrated that specialization decreased with elevation across networks, communities, and pollinator species. Temperature predicted the degree of specialization better than pollinator richness, resource availability, area, or pollinator traits. Despite the mechanisms behind the patterns have yet to be fully resolved, we conclude that temperature shifts in the course of climate change may destabilize pollination networks by affecting network architecture.
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