Thermal tolerance of sympatric hymenopteran parasitoid species: does it match seasonal activity?

Climatic changes result in an increased in mean temperature and in a higher incidence of extreme weather events such as heat and cold waves. For ectotherms, such as insect parasitoids, the ability to remain active under extreme climatic conditions is a significant key to fitness. The body size of individuals, and in particular their surface to volume ratio, may play a role in their resistance to thermal conditions. The thermal tolerances are investigated of two closely‐related sympatric parasitoid species [Aphidius avenae Haliday and Aphidius rhopalosiphi De Stefani‐Perez (Hymenoptera: Aphidiinae)] that have a similar ecology but differ in body size and phenologies. The critical thermal limits of individuals are assessed in both sexes of each parasitoid species and the influence of surface–volume ratios on their thermal tolerances. Aphidius avenae is less resistant to low temperatures and more resistant to high temperatures than A. rhopalosiphi. The lower surface to volume ratio of A. avenae individuals may help them to remain active in summer when experiencing heat waves. However, body size is not the sole factor that plays a role in differences of thermal tolerance between species and body size may not be an adaptation to extreme temperatures but rather a by‐product of developmental regulation. Closely‐related sympatric species from the same ecological guild can have different thermal tolerances that may allow them to occur within the same habitat. The present study also highlights the importance of clearly defining how to measure critical thermal limits to determine the thermal tolerance of a species.     

Interspecific relations in forest floor coleopteron assemblages: Niche overlap and guild structure

In six different environments of the Towada-Hachimantai National Park, the forest floor coleopterons were sampled by means of pitfall traps with five different baits. Their niche breadths and niche overlaps were assessed for the electivity of habitat, bait, and habitat × bait, and compared with those expected from neutral models constructed randomly. The niche breadths in the observed assemblages were smaller than those expected from the neutral model, while the niche overlaps were more widely distributed than those expected from the neutral model. Mean overlaps between species neighbors in niche space, cluster analyses, and ordinations of species revealed a guild for habitat, bait and habitat × bait. Lawlor's (1979) gamma matrices concerning the habitat electivity show that the rates of mutualism resulted from indirect interspecific competitions are significantly smaller in the guild than in the whole assemblage. This suggests that the interspecific competition among the guild members is mitigated or even converted into mutualism by joining of the species which do not belong to the guild. The rates of mutualism were also significantly larger in the resource state of two dimensions (habitat × bait) than in that of either one. Therefore, if niche overlaps are measured on the basis of resource state of multi-dimensions, the rates of mutualism may increase further.     

Fish feeding guilds in shallow rocky and soft bottom areas on the Swedish west coast

Multivariate analyses of the diet relationships within fish assemblages resulted in the recognition of five major feeding guilds in shallow (0-9 m) rocky- and soft-bottom habitats on the Swedish west coast. The two habitats had similar guilds that could be broadly described as piscivores, decapod feeders, copepod feeders and amphipod and mollusc feeders. The last guild on the rocky bottom was more strictly one of amphipod feeders, whereas the last guild on soft bottoms consisted of infauna feeders (mainly polychaetes and bivalves). A comparison of the diet of the entire fish assemblages showed that amphipods and gastropods were more prevalent as prey taxa on rocky bottoms, whereas bivalves and teleosts were more common on soft bottoms. A large proportion (12 out of 27 species) of the fish species investigated was found in both habitats. These fish species generally seemed to rely on the same major prey groups in the two habitats, but also included prey taxa characteristic for the habitat in which they resided. Sea trout Salmo trutta , mackerel Scombrus scombrus , saithe Pollachius virens , whiting Merlangius merlangus and cod Gadus morhua were found to be the major piscivores in both the investigated habitats. Herring Clupea harengus and members of the family gobiidae were the most prevalent prey species for piscivores within the rocky- as well as the soft-bottom fish assemblage. A comparison of feeding modes suggested that the fish assemblage on rocky bottoms predominantly (60% of the food items) relied on food found in vegetation. On soft bottoms, the average distribution of food categories among fish species was 44% benthic, 35% pelagic and 21% vegetation-associated food items.     

Arthropod community structure along a latitudinal gradient: Implications for future impacts of climate change

Abstract The structure of free‐living arthropod communities on the foliage of Acacia falcata was assessed along an extensive latitudinal gradient in eastern Australia. We hypothesized that abundance and biomass of arthropods within feeding groups would increase from temperate latitudes towards the tropics. We also hypothesized that the ratio of carnivores to herbivores would be consistent along the latitudinal gradient. Three sites at each of four latitudes, spanning 9° and 1150 km (Batemans Bay, Sydney, Grafton, Gympie in Australia), were sampled every season for 2 years, using pyrethrum knockdown. Abundance and biomass (based on dry weight) of arthropods within eight feeding groups were measured. The relative size of the feeding groups, and the ratio of carnivores to herbivores were then compared among latitudes and seasons. We found no consistent north to south (tropical to temperate) change in feeding group structure in terms of abundance. A weak latitudinal trend was evident for predator biomass, consisting of a reduction from north to south, but no significant trends in biomass for other feeding groups were found. Relative abundance and relative biomass of both carnivores and herbivores, as well as the ratio of carnivores to herbivores were consistent among latitudes. Finally, we compared a subset of these data to arthropod communities found on congeneric host species at individual sites along the latitudinal gradient. Overall, 68% of comparisons showed no significant differences in abundance or biomass within different feeding groups between host plants and among latitudes. We conclude that arthropod communities show consistencies among latitudes and between congeneric host species, in terms of feeding group and trophic structure. These results have implications for predicting the impacts of future climate change on arthropod communities.     

Assembly processes of trophic guilds in the root mycobiome of temperate forests

Root‐associated mycobiomes (RAMs) link plant and soil ecological processes, thereby supporting ecosystem functions. Understanding the forces that govern the assembly of RAMs is key to sustainable ecosystem management. Here, we dissected RAMs according to functional guilds and combined phylogenetic and multivariate analyses to distinguish and quantify the forces driving RAM assembly processes. Across large biogeographic scales (>1,000 km) in temperate forests (>100 plots), RAMs were taxonomically highly distinct but composed of a stable trophic structure encompassing symbiotrophic, ectomycorrhizal (55%), saprotrophic (7%), endotrophic (3%) and pathotrophic fungi (<1%). Taxonomic community composition of RAMs is explained by abiotic factors, forest management intensity, dominant tree family (Fagaceae, Pinaceae) and root resource traits. Local RAM assemblies are phylogenetically clustered, indicating stronger habitat filtering on roots in dry, acid soils and in conifer stands than in other forest types. The local assembly of ectomycorrhizal communities is driven by forest management intensity. At larger scales, root resource traits and soil pH shift the assembly process of ectomycorrhizal fungi from deterministic to neutral. Neutral or weak deterministic assembly processes are prevalent in saprotrophic and endophytic guilds. The remarkable consistency of the trophic composition of the RAMs suggests that temperate forests attract fungal assemblages that afford functional resilience under the current range of climatic and edaphic conditions. At local scales, the filtering processes that structure symbiotrophic assemblies can be influenced by forest management and tree selection, but at larger scales, environmental cues and host resource traits are the most prevalent forces.     

Bird dietary guild richness across latitudes,environments and biogeographic regions

Aim To integrate dietary knowledge and species distributions in order to examine the latitudinal, environmental, and biogeographical variation in the species richness of avian dietary guilds (herbivores, granivores, frugivores, nectarivores, aerial insectivores, terrestrial/arboreal insectivores, carnivores, scavengers, and omnivores). Location Global. Methods We used global breeding range maps and a comprehensive dietary database of all terrestrial bird species to calculate guild species richness for grid cells at 110 × 110 km resolution. We assessed congruence of guild species richness, quantified the steepness of latitudinal gradients and examined the covariation between species richness and climate, topography, habitat diversity and biogeographic history. We evaluated the potential of current environment and biogeographic history to explain global guild distribution and compare observed richness–environment relationships with those derived from random subsets of the global species pool. Results While most guilds (except herbivores and scavengers) showed strong congruence with overall bird richness, covariation in richness between guilds varied markedly. Guilds exhibited different peaks in species richness in geographical and multivariate environmental space, and observed richness–environment relationships mostly differed from random expectations. Latitudinal gradients in species richness were steepest for terrestrial/arboreal insectivores, intermediate for frugivores, granivores and carnivores, and shallower for all other guilds. Actual evapotranspiration emerged as the strongest climatic predictor for frugivores and insectivores, seasonality for nectarivores, and temperature for herbivores and scavengers (with opposite direction of temperature effect). Differences in species richness between biogeographic regions were strongest for frugivores and nectarivores and were evident for nectarivores, omnivores and scavengers when present‐day environment was statistically controlled for. Guild richness–environment relationships also varied between regions. Main conclusions Global associations of bird species richness with environmental and biogeographic variables show pronounced differences between guilds. Geographic patterns of bird diversity might thus result from several processes including evolutionary innovations in dietary preferences and environmental constraints on the distribution and diversification of food resources.     

Ecological effects of multi‐species,ant–hemipteran mutualisms in citrus

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Monitoring fungi in ecological restorations of coastal Indiana,U.S.A.

Monitoring of ecological restorations has rarely focused on fungi. In this study, we conduct a first‐ever monitoring of macrofungi in ecological restorations of coastal Indiana (U.S.A.) and present an approach and considerations that can be followed elsewhere. Forty‐two sites were surveyed over a 2‐year period for the presence of saprotrophic, mycorrhizal, and parasitic macrofungi. Sites included those considered to be restoration, prerestoration, or reference and were in wooded, semiwooded, or grassland habitats. With 1,103 observations, 277 species of fungi were identified. Most fungi were found in wooded habitats though some were in grassland restorations. Invasive plant cover negatively impacted fungal species richness. Monitored sites were compared to a set of reference sites using two different similarity indices (overlap and Jaccard), as well as the ratios of different fungal functional guilds, revealing that choice of index can impact how restorations are perceived to match targets. Last, we present a novel, tractable, and conservative way to assess and rank sites by the functional trait guilds of fungi. We show that such an approach can provide important additional information about the success of restorations such that functional guild ratios could be used as an indicator of restoration progress early‐on while functional values are better used in later phases.