An overview of proximate factors affecting the nesting behavior of solitary wasps and bees (Hymenoptera: Aculeata) in preexisting cavities in wood

Guilds of Aculeate solitary wasps and bees that nest in preexisting cavities in wood are important components of terrestrial ecosystems because they engage in several ecological interactions (e.g. predation and pollination) with other species of plants and animals. Spatial and temporal variations in richness and abundance of solitary wasps and bees can be related to changes in environmental structure and in the diversity of other groups of organisms. The nesting period of these Aculeata is their most critical life cycle stage. Females of solitary wasp and bee species invest relatively more time constructing and provisioning their nests than do females of social species. Differently from species that nest in the soil or construct exposed nests, the main factors affecting the reproductive success of solitary species nesting in preexisting wood holes are still unknown. Our objective is to provide an overview of the role of proximate causes of nesting failure or success among solitary wasps and bees (Aculeata), for designing effective conservation and management strategies for these Hymenoptera.     

Analysis of trophic structure of two carnivore assemblages by means of guild identification

We evaluated the existence of trophic guild structure, considering seasonal and annual variation, in two terrestrial carnivore assemblages: one from Santa Cruz province (Argentinean Patagonia, composed by six carnivore species), and the other from Doñana National Park (SW Spain, composed by five carnivore species). To identify trophic guilds, we first studied seasonal and annual diets of predators, calculated trophic overlap among species pairs, and then constructed overlap matrices (similarity matrices). We determined guild membership objectively by entering the similarity matrices into the clustering technique unweighted pair-group method with arithmetic averaging. Carnivores from both assemblages were grouped, respectively, into four feeding guilds. Lagomorphs and rodents promoted the formation of two feeding guilds in both study sites, although the taxonomic composition of predator species that composed them was different. The ungulates-edentates feeding guild was only present at Santa Cruz, whereas the birds and reptiles feeding guild was only present at Doñana. Invertebrates and fruits were the base for the formation of a guild composed by species of the same taxonomic origin both in Santa Cruz and Doñana. Guild structure of Santa Cruz and Doñana assemblages did not exhibit seasonal or annual variation, although the specific guild composition changed over the two studied periods for both assemblages. This structure probably responded to discontinuities in resource spectra in Santa Cruz and fluctuations in rabbit abundance in Doñana. Our results support the hypothesis that establishes that guilds are originated by opportunistic convergence of species on abundant and energetically rewarding resources.     

Different responses of avian feeding guilds to spatial and environmental factors across an elevation gradient in the central Himalaya

Although elevational patterns of species richness have been well documented, how the drivers of richness gradients vary across ecological guilds has rarely been reported. Here, we examined the effects of spatial factors (area and mid‐domain effect; MDE) and environmental factors, including metrics of climate, productivity, and plant species richness on the richness of breeding birds across different ecological guilds defined by diet and foraging strategy. We surveyed 12 elevation bands at intervals of 300 m between 1,800 and 5,400 m a.s.l using line‐transect methods throughout the wet season in the central Himalaya, China. Multiple regression models and hierarchical partitioning were used to assess the relative importance of spatial and environmental factors on overall bird richness and guild richness (i.e., the richness of species within each guild). Our results showed that richness for all birds and most guilds displayed hump‐shaped elevational trends, which peaked at an elevation of 3,300–3,600 m, although richness of ground‐feeding birds peaked at a higher elevation band (4,200–4,500 m). The Normalized Difference Vegetation Index (NDVI)—an index of primary productivity—and habitat heterogeneity were important factors in explaining overall bird richness as well as that of insectivores and omnivores, with geometric constraints (i.e., the MDE) of secondary importance. Granivore richness was not related to primary production but rather to open habitats (granivores were negatively influenced by habitat heterogeneity), where seeds might be abundant. Our findings provide direct evidence that the richness–environment relationship is often guild‐specific. Taken together, our study highlights the importance of considering how the effects of environmental and spatial factors on patterns of species richness may differ across ecological guilds, potentially leading to a deeper understanding of elevational diversity gradients and their implications for biodiversity conservation.     

Three pollination guilds and variation in floral characteristics of Bornean gingers (Zingiberaceae and Costaceae)

The pollinators of 29 ginger species representing 11 genera in relation to certain floral morphological characteristics in a mixed-dipterocarp forest in Borneo were investigated. Among the 29 species studied, eight were pollinated by spiderhunters (Nectariniidae), 11 by medium-sized Amegilla bees (Anthophoridae), and ten by small halictid bees. These pollination guilds found in gingers in Sarawak are comparable to the pollination guilds of neotropical Zingiberales, i.e., hummingbird-, and euglossine-bee-pollinated guilds. Canonical discriminant analysis revealed that there were significant correlations between floral morphology and pollination guilds and suggests the importance of plant–pollinator interactions in the evolution of floral morphology. Most species in the three guilds were separated on the plot by the first and second canonical variables. Spiderhunter-pollinated flowers had longer floral tubes, while Amegilla-pollinated flowers had wider lips than the others, which function as a platform for the pollinators. Pistils and stamens of halictid-pollinated flowers were smaller than the others. The fact that gingers with diverse morphologies in a forest with high species diversity were grouped into only three pollination guilds and that the pollinators themselves showed low species diversity suggests that many species of rare understory plants have evolved without segregating pollinators in each pollination guild.     

Tree diversity promotes predatory wasps and parasitoids but not pollinator bees in a subtropical experimental forest

From regional to global scales, anthropogenic environmental change is causing biodiversity loss and reducing ecosystem functionality. Previous studies have investigated the relationship between plant diversity and functional insect communities in temperate and also in tropical grasslands and forests. However, few studies have explored these dynamics in subtropical forests. Here, cavity-nesting Hymenoptera and associated parasitoids were collected across a controlled tree diversity experiment in subtropical China to test how predatory wasps, bees and parasitoids respond to tree species richness. Abundance and species richness of predatory wasps and parasitoids were positively correlated with tree species richness, while bee abundance and bee species richness were unrelated to tree species richness. Our results indicate that tree species richness increases the abundance and species richness of important communities such as predators and parasitoids. Moreover, the results highlight the importance of subtropical forests in maintaining abundance and species richness of key functional insect groups.     

Effect of elevation on the insect herbivory of Mongolian oaks in the high mountains of southern South Korea

Elevation is strongly associated with the diversity and ecology of plants and animals. We explored how elevation affects herbivores on one of the major cool-temperate trees, Quercus mongolica, in southern South Korea. The feeding activities of insect herbivores were measured through insect-feeding damage on leaves. Of 78 types of insect-feeding damage that were observed from Jirisan Mountain (Mount.) and Hallasan Mount. in Korea, 61.6% was associated with externally feeding insects. The sum of feeding damages per leaf was significantly higher on Jirisan Mount. than on Hallasan Mount., and higher at higher elevation in both mountains. Two feeding guilds, externally feeding, and piercing and sucking were strongly related with elevation, but the relationship was opposite depending on feeding guild. Leaf damage by the internal feeding guild showed no effect of elevation at the two mountains. These study results showed that insect herbivory responds to elevational differences in temperate forests, and that such response can vary among feeding guilds.     

Reprint of: Tree diversity promotes predatory wasps and parasitoids but not pollinator bees in a subtropical experimental forest

From regional to global scales, anthropogenic environmental change is causing biodiversity loss and reducing ecosystem functionality. Previous studies have investigated the relationship between plant diversity and functional insect communities in temperate and also in tropical grasslands and forests. However, few studies have explored these dynamics in subtropical forests. Here, cavity-nesting Hymenoptera and associated parasitoids were collected across a controlled tree diversity experiment in subtropical China to test how predatory wasps, bees and parasitoids respond to tree species richness. Abundance and species richness of predatory wasps and parasitoids were positively correlated with tree species richness, while bee abundance and bee species richness were unrelated to tree species richness. Our results indicate that tree species richness increases the abundance and species richness of important communities such as predators and parasitoids. Moreover, the results highlight the importance of subtropical forests in maintaining abundance and species richness of key functional insect groups.     

Experimental effects of habitat fragmentation on old-field canopy insects: community, guild and species responses

We examined the effects of habitat fragmentation on the species distributions, guild membership, and community structure of old-field insects using a fine-scale experimental approach. A continuous 1-ha goldenrod field was fragmented into four treatments that varied in both patch size and degree of isolation. Each treatment was replicated four times and arranged in a Latin square design. Canopy insects in fragmented patches were sampled with sweep nets during early and late summer 1995. The species richness of insects was significantly lower in fragmented than in unfragmented treatments during July, but was similar among treatments in September. Overall community abundance showed no treatment effect during either month. We also found significant row and column effects, suggesting there was spatial heterogeneity in species richness and abundance apart from treatment effects. Differences in species richness during July were primarily due to the loss of rare species in highly fragmented plots. Overall abundance was less responsive to community change because deletions of rare species in fragmented areas were not detected in abundance analyses. Four feeding guilds showed different responses to fragmentation: the species richness of sucking herbivores and the abundance of parasitoids were significantly reduced by fragmentation but predators and chewing herbivores were largely unaffected. Analyses of a subset of individual species within guilds suggest that the greater effects of fragmentation on sucking herbivores and parasitoids may be due to the degree of habitat specificity of guild members. The effects of small-scale habitat fragmentation were therefore detectable at the level of community, guild, and individual species. Changes in species richness, guild structure and species distributions were likely due to differential effects of habitat alteration on individual movements and patch selection rather than dispersal or demographic change. Nonetheless, the selective loss of rare species, differential guild effects and changes in species occupancy that we found in this small-scale experiment are also factors that are likely to operate in fragmented habitats over broader spatial scales. Received: 11 May 1998 / Accepted: 27 September 1998     

Inter‐assemblage facilitation: the functional diversity of cavity‐producing beetles drives the size diversity of cavity‐nesting bees

Inter‐specific interactions are important drivers and maintainers of biodiversity. Compared to trophic and competitive interactions, the role of non‐trophic facilitation among species has received less attention. Cavity‐nesting bees nest in old beetle borings in dead wood, with restricted diameters corresponding to the body size of the bee species. The aim of this study was to test the hypothesis that the functional diversity of cavity‐producing wood boring beetles ‐ in terms of cavity diameters ‐ drives the size diversity of cavity‐nesting bees. The invertebrate communities were sampled in 30 sites, located in forested landscapes along an elevational gradient. We regressed the species richness and abundance of cavity nesting bees against the species richness and abundance of wood boring beetles, non‐wood boring beetles and elevation. The proportion of cavity nesting bees in bee species assemblage was regressed against the species richness and abundance of wood boring beetles. We also tested the relationships between the size diversity of cavity nesting bees and wood boring beetles. The species richness and abundance of cavity nesting bees increased with the species richness and abundance of wood boring beetles. No such relationship was found for non‐wood boring beetles. The abundance of wood boring beetles was also related to an increased proportion of cavity nesting bee individuals. Moreover, the size diversity of cavity‐nesting bees increased with the functional diversity of wood boring beetles. Specifically, the mean and dispersion of bee body sizes increased with the functional dispersion of large wood boring beetles. The positive relationships between cavity producing bees and cavity nesting bees suggest that non‐trophic facilitative interactions between species assemblages play important roles in organizing bee species assemblages. Considering a community‐wide approach may therefore be required if we are to successfully understand and conserve wild bee species assemblages in forested landscapes.     

The Role of Passive Defense (Selfish Herd and Dilution Effect) in the Gregarious Nesting of Liostenogaster Wasps (Vespidae, Hymenoptera, Stenogastrinae)

The advantages of the selfish herd and encounter-dilution effects were studied in two congeneric gregarious-nesting species of Stenogastrine wasps, Liostenogaster vechti Turillazzi and L. flavolineata (Cameron), in Malaysia. Results show that nesting in clusters affords these wasps some degree of protection against their main invertebrate predators, parasites and parasitoids. This advantage is reflected in the geometry of the aggregation as well as in the behavior of the individuals. The costs and benefits of group living and the implications of the selection of this nesting strategy in the evolution of sociality in these wasps are discussed.     

Variation in the guild composition of herbivorous insect assemblages among co‐occurring plant species

Variation in plant traits among plant species may promote the development of a characteristic functional assemblage of insect herbivores associated with each plant species. However, only a small number of studies have detailed the representation of several herbivore guilds among co‐occurring plant species to determine whether the functional structure of herbivorous insect assemblages varies widely and consistently among plant species. The present study provides one of the few published data sets reporting on the density of several guilds of insect herbivores among numerous plant species. Variation in guild associations with plant phenology and season are also described. Insect herbivores were divided into 10 guilds, and the representation of these guilds was examined for 18 co‐occurring plant species. Guild densities and assemblage composition varied significantly among plant species, even when variation over time was taken into account. Variation in guild densities and assemblage composition were not strongly related to the taxonomic relationships of the plants. The highest densities of several guilds occurred in spring and summer, although other guilds were not strongly seasonal. Certain guilds were strongly associated with the presence of new leaves, whereas other guilds appeared to prefer mature leaves. This resulted in assemblage differences between samples containing new and mature leaves and samples containing mature leaves only. Even though the timing and duration of leaf and flower production varied among plant species, this did not explain all variation in guild densities among plant species. It is suggested that additional factors, including plant traits, are contributing to the wide and consistent variation in herbivore assemblage composition among plant species.     

The influence of climatic seasonality on the diversity of different tropical pollinator groups

Tropical South America is rich in different groups of pollinators, but the biotic and abiotic factors determining the geographical distribution of their species richness are poorly understood. We analyzed the species richness of three groups of pollinators (bees and wasps, butterflies, hummingbirds) in six tropical forests in the Bolivian lowlands along a gradient of climatic seasonality and precipitation ranging from 410 mm to 6250 mm. At each site, we sampled the three pollinator groups and their food plants twice for 16 days in both the dry and rainy seasons. The richness of the pollinator groups was related to climatic factors by linear regressions. Differences in species numbers between pollinator groups were analyzed by Wilcoxon tests for matched pairs and the proportion in species numbers between pollinator groups by correlation analyses. Species richness of hummingbirds was most closely correlated to the continuous availability of food, that of bees and wasps to the number of food plant species and flowers, and that of butterflies to air temperature. Only the species number of butterflies differed significantly between seasons. We were not able to find shifts in the proportion of species numbers of the different groups of pollinators along the study gradient. Thus, we conclude that the diversity of pollinator guilds is determined by group-specific factors and that the constant proportions in species numbers of the different pollinator groups constitute a general pattern.     

Feeding habits and seasonal trophic guilds structuring fish community in the bay mouth region of a tropical estuarine habitat

Understanding trophic relationships of fish in estuarine ecosystem is an important element for sustainable resource management. This study examined the feeding habits of 29 dominant fish species, characterized the trophic guilds, assessed the impact of season and clarified the role of diets in structuring the fish community in the mouth region of Pattani Bay, Thailand. Samples of 5792 fishes collected monthly by gillnets from March 2019 to February 2020 were used for stomach content analyses. It was found that the number of food types and fullness index differed between fish taxa (P < 0.001). Most fishes were specialist feeders feeding on specific food components and were categorized into five trophic guilds: piscivore, shrimp-fish feeder, polychaete feeder, zooplanktivore and planktivore. Six species were piscivorous, considered as apex predators, that fed almost entirely on fishes. High diet overlaps among some species (>0.6) were recorded. Not much variation in seasonal guilds was observed: four guilds in the dry season, three in the moderate rainy season and four in the rainy season. Some species remained in the same guild the whole year round, but some fishes changed seasonally. Two fish communities from different regions of the bay were segregated based on feeding habits. The inner bay community comprised mainly copepod and plankton feeders, but there were more piscivores in the deeper bay mouth area. Results from this study help us to understand the feeding habits and trophic guilds of dominant fish species at the mouth of this tropical estuarine bay.     

Plant–pollinator interactions in the understory of a lowland mixed dipterocarp forest in Sarawak

Pollination biology of 41 plants species of 21 families blooming in the forest understory was investigated in a lowland mixed diplerocarp forest in Lambir Hills National Park, Sarawak. Among these species, 29 species (71%) were pollinated by bees, four (10%) by nectariniid birds, three by small dipterans, and others by moths, butterflies, syrphid flies, wasps, and beetles. The 29 bee-pollinated species consisted of five distinct pollination guilds: ten species pollinated by medium traplining bees (two Amegilla species), nine by small traplining bees (three halictid and a xylocopine species), two by stingless bees and beetles, seven by stingless bees, and one by megachilid bees. The bees constituting the first two guilds were shade-loving, swiftly flying, long-tongued trapliners. Proboscis lengths of these pollinators correlated with flower depth of the host plant. Pollination systems in the forest understory were distinguished from that in the canopy by the prevalence of specific interactions, the number of traplining solitary bees, and lack of pollination systems by mass-recruiting eusocial bees, large Xylocopa bees, thrips, bats, and wind. These characteristics are largely similar between the Palaeotropics and the Neotropics through convergence of nectarivorous birds (spiderhunters vs. hummingbirds) and traplining bees (Amegilla vs. euglossine bees).     

Seasonal dynamics of guild structure in a bird assemblage of the central Monte desert

Most studies of ecological guilds consider guild membership as a fixed attribute of species, and the guild structure as a fixed attribute of a community. Consequently, almost no study tackled the examination of temporal changes in the guild structure of a particular assemblage. We used data on foraging patterns of central Monte desert birds to assess seasonal differences in resource use by resident species, and to examine seasonal changes in the guild structure of the assemblage. From 1993 until 1999, we quantified the use of foraging substrates, manoeuvres, and height strata, and the utilisation of plants by 18 bird species. Resident species showed different kinds of seasonal dynamics, from no noticeable to drastic changes in their foraging patterns. Seasonal changes in guild structure were remarkable. Only two guilds were present all year round (ground foragers and foliage foragers), although they suffered important species turnover. Three other guilds had a seasonal occurrence: graminivores (during the non-breeding season), arboreal herbivores, and aerial feeders (during the breeding season). Two species changed from one guild to another between seasons. Both presence–absence of migrant species, and changes in the feeding ecology of resident species had an influence on the temporal dynamics of guild structure. These factors appeared to be related with changing resource availability, especially with the birds’ ability for facing lean conditions through migration and with the opportunistic use of seasonally superabundant resources. Our results undermine the trust in studies in which guild structure was assessed irrespective of temporal variations. We show also that guild membership is not a fixed attribute of a species: we should rather evaluate the individuals’ resource use in a given moment to assign them to a guild, instead of obtaining a single measure purporting to represent a species’ fixed attribute.     

Elevation and experimental snowmelt manipulation affect emergence phenology and abundance of soil‐hibernating arthropods

1. Effects of climate change, such as higher average temperatures and earlier snowmelt, are already apparent, especially in alpine regions. However, community responses of functionally important arthropod taxa to changing climatic conditions are mostly unknown. 2. In this study, an earlier snowmelt was simulated at 15 plots along an elevational gradient in the German Alps. At each study site, soil emergence traps were established for sampling soil‐hibernating arthropods on earlier and control snowmelt treatments during the growing season. The abundance and emergence phenology of the five most common arthropod orders (Araneae, Coleoptera, Diptera, Hemiptera, Hymenoptera) were analysed, as well as the species richness of Coleoptera. 3. There was increasing abundance and species richness of Coleoptera along the elevational gradient, indicating that at higher altitudes more individuals and species hibernate in the soil. Abundances of Diptera also increased with elevation. By contrast, abundances of Hemiptera declined with increasing elevation, while abundances of Araneae and Hymenoptera did not show significant elevational patterns. Arthropods at higher elevations emerged, on average, 5 weeks later than arthropods at lower elevations, because of a longer‐lasting snow cover. The earlier snowmelt treatment resulted in higher abundances of Araneae and Hymenoptera compared with the control plots, indicating that the time of snowmelt influenced the abundance of predators, such as spiders or parasitic wasps, more than that of herbivores. 4. An earlier emergence of certain arthropod guilds and a change in relative abundance of guilds might desynchronise species interactions, leading to a possible loss of biodiversity.     

The structure and components of European estuarine fish assemblages

This paper discusses the structure of fish assemblages using information from 17 European estuarine areas (in the British Isles, Portugal, Belgium, France, the Netherlands, Germany, Norway and Spain). Binary (presence/absence) and quantitative data for each assemblage have been used to assess the assemblage structure according to taxonomy (i.e. species identity). Following this, a total of 29 functional guilds were created in order to describe the use made of an estuarine area for each taxon encountered: feeding preferences, reproduction type, substratum preferences (for bottom dwelling fish) and position within the water column (vertical preference guild). The paper focuses on the designation and determination of the proportions of the guild members of the fish assemblage within each estuary. Ecological guilds within the assemblage include estuarine residents, marine juvenile migrants, catadromous and anadromous migrants, marine seasonal users, and freshwater and marine adventitious species. Feeding guilds include detritivores, planktonic feeders, infaunal croppers and sediment ingesters, piscivores, and active predators of mobile crustaceans. Reproduction guilds include planktonic and demersal spawners and those using brood-protection. The substratum preference indicates the proportions of sand, mud, rock and vegetation dwellers, and the vertical preference denotes benthic, demersal or pelagic species. The analysis has allowed both the estuaries to be grouped according to taxonomic and guild similarity and the characterisation of a typical European estuarine fish assemblage. Within the limits posed by differing sampling methods, times of sampling and survey rationale, there is a high similarity between estuaries. The data indicate common patterns of estuarine usage irrespective of the differences between the estuaries although such patterns cannot be interpreted fully given the incomplete knowledge of their physical and anthropogenic characteristics.     

Pollination and parasitism in functionally dioecious figs

Fig wasps (Agaonidae: Hymenoptera) are seed predators and their interactions with Ficus species (Moraceae) range from mutualism to parasitism. Recently considerable attention has been paid to conflicts of interest between the mutualists and how they are resolved in monoecious fig species. However, despite the fact that different conflicts can arise, little is known about the factors that influence the persistence of the mutualism in functionally dioecious Ficus. We studied the fig pollinator mutualism in 14 functionally dioecious fig species and one monoecious species from tropical lowland rainforests near Madang, Papua New Guinea. Observations and experiments suggest that (i) pollinating wasps are monophagous and attracted to a particular host species; (ii) pollinating and non-pollinating wasps are equally attracted to gall (male) figs and seed (female) figs in functionally dioecious species; (iii) differing style lengths between gall figs and seed figs may explain why pollinators do not develop in the latter; (iv) negative density dependence may stabilize the interaction between pollinating wasps and their parasitoids; and (v) seed figs may reduce the search efficiency of non-pollinators. This increased pollinator production without a corresponding decrease in seed production could provide an advantage for dioecy in conditions where pollinators are limiting.     

Organization of a parasitoid community associated with a complex of galls on Atriplex spp. in southern California

Abstract. 1. Atriplex canescens (Pursh) Nuttall and A.polycarpa (Torrey) Watson (Chenopodiaceae) support twelve morphologically distinct gall types in southern California. Thirty-seven common species of parasitoids, predators and inquilines are associated with these galls. 2. The galls incited by eight members of the Asphondylia atriplicis Cockerell (Diptera: Cecidomyiidae) species complex are linked into a single, interacting community through shared hymenopterous parasitoids and inquilines. 3. Cluster analysis (UPGMA) grouped the fifteen most common species of Chalcidoidea into three host guilds of five species each: (1) specialists in tumour stem and blister leaf galls on A.canescens, (2) specialists in woolly stem galls on A.poiycarpa, and (3) generalists that attack all galls. Guild 1 dominated the galls with which it was primarily associated, while guild 3 dominated the remainder. 4. The abundances of the parasitoids of the tumour stem and blister leaf galls were negatively correlated with the abundances of two organizer species, a gall-forming inquiline, Tetrastichus cecidobroter Gordh and Hawkins, and an internal, larval—pupal parasitoid, Tetrastichus sp. B. The abundances of nine of the twelve most common chalcidoids were not correlated with the abundances of all coaccurring species in six other galls. 5. Host seasonality partly determines parasitoid population dynamics and guild structure. Parasitoid dominance increased with gall duration, suggesting that parasitoid competition depends on resource stability. The two continuously available galls were dominated by their specialist guild, while all seasonal galls were dominated by generalists. The subdominant specialists of woolly stem galls may represent competitively inferior species that utilize those galls opportunistically, because of the gall's widespread distribution and 9–10 month yearly availability. 6. Sites in the Colorado Desert and chaparral that supported several gall types showed stable relative abundances of the major parasitoid species, whereas sites in the Mojave Desert that supported only woolly stem galls had unpredictable parasitoid species assemblages. 7. The competitive success of Atriplex gall parasitoids may depend primarily on voltinism (multivoltine species dominated univoltine species) and mode of feeding (phytophagous, mixed entomophagous—phytophagous and facultatively hyperparasitic species in general dominated strict primary parasitoids).     

Changes in function and temporal variation in a guild of gall‐parasitoids across a temperature gradient in Australian subtropical rainforest

Parasitoids play an important role in ecosystem functioning through their influence on herbivorous insect populations. Theoretical and experimental evidence suggest that increased species richness can enhance and stabilize ecosystem function. It is important to understand how richness‐driven functional relationships change across environmental gradients. We investigated how temperature affected the relationship between parasitoid richness and parasitism rate in a guild of gall‐parasitoids along an elevational gradient. We collected galls at 15 sites along five elevational gradients (between 762 m and 1145 m asl) on six occasions over a year. A total of 1902 insects, including 1593 parasitoids, were reared from 12 402 galls. Parasitism rate increased significantly with temperature on all sampling occasions, except December and February. We found a significant, positive richness–parasitism relationship. This relationship, however, was weaker at higher elevations which may be linked to decreased functional efficiency of parasitoids at lower temperatures. Temporal variability in parasitism rate and parasitoid richness were significantly related, regardless of temperature. A stable functional guild of this kind may provide a more reliable ecosystem service under environmental changes.