Main Guilds Research Articles

Divergent effects of drought and nitrogen deposition on microbial and arthropod soil communities in a Mediterranean forest

Drivers of global change such as warming and increased nitrogen (N) availability are altering soil communities worldwide, with unknown consequences for the functioning of the terrestrial ecosystems. Higher N availability may stimulate soil communities and boost nutrient cycling, but the expected increase in aridity may nullify this effect. Additionally, shifts in microbial communities may lead to trophic cascades throughout soil food webs, affecting key ecosystem properties associated with the turnover of carbon and nutrients. Whether the responses to these different drivers of global change are similar between the main guilds of soil organisms, however, is unclear. We analyzed soil phospholipid fatty acids and extracted soil fauna to determine the simultaneous responses of microbial and arthropod soil communities to experimental drought and increased N availability in a Mediterranean forest. The experimental drought decreased community sizes across the entire soil food web, and N addition increased the biomass of all microbial groups except fungi, thereby increasing the relative dominance of bacteria. Likewise, the abundance of oribatid mites strongly increased after the addition of N, whereas the population of springtails quickly decreased, leading to a shift in the structure of the arthropod community. An increase in soil N availability promoted the energy channel dominated by bacteria, triggering a bottom-up trophic cascade affecting the arthropod mesofauna, thus propagating the effects of N inputs throughout the soil food web. The strong constraint of drought on soil microbes, however, may neutralize the effect of an increase in N availability. Complex interactions among factors of global change may therefore hinder our ability to predict their effects on soil biodiversity and associated consequences for ecosystem functioning. Forecasts of responses of soil biodiversity to global change should not only consider different drivers and their potential interactions, but also the likely contrasting effects among different groups of soil organisms.

Testing for top-down cascading effects in a biomass-driven ecological network of soil invertebrates.

To investigate the structural changes of a food‐web architecture, we considered real data coming from a soil food web in one abandoned pasture with former low‐pressure agriculture management and we reproduced the corresponding ecological network within a multi‐agent fully programmable modeling environment in order to simulate dynamically the cascading effects due to the removal of entire functional guilds.We performed several simulations differing from each other for the functional implications. At the first trophic level, we simulated a removal of the prey, that is, herbivores and microbivores, while at the second trophic level, we simulated a removal of the predators, that is, omnivores and carnivores. The five main guilds were removed either separately or in combination.The alteration in the food‐web architecture induced by the removal of entire functional guilds was the highest when the entire second trophic level was removed, while the removal of all microbivores caused an alteration in the food‐web structure of less than 5% of the total changes due to the removal of opportunistic and predatory species.Omnivores alone account for the highest shifts in time of the numerical abundances of the remaining species, providing computational evidence of the importance of the degree of omnivory in the stabilization of soil biota.

Responses of fungal community structure and functional group to fertilization in yellow clayey soil.

We investigated the responses and underlying mechanisms of community composition, and function group of fungi in yellow clayey paddy soil to different long-term fertilization, which may provide scientific basis for rational fertilization and sustainable development in agriculture ecosystems. There were four treatments, including control (CK), inorganic fertilizer (NPK), inorganic fertilizer combined with manure (NPKM), and inorganic fertilizer combined with straw (NPKS). Illumina high-throughput sequencing and FUNGuild were performed to investigate the fungal community structure and functional group, respectively. Ascomycota, Basidiomycota, and Zygomycota were identified as the three dominant ones. The proportion of Ascomycota in NPKM and NPKS were significantly lower (49% and 47%, respectively) compared with CK (71%) and NPK (74%) treatments, with the main reduced orders of Hypocreales, Pleosporales and Eurotiales. While there was higher relative abundance of Basidiomycota in NPKM and NPKS (18% and 28%) compared to CK (14%) and NPK (10%), the orders with enhancement were Tremellales, Trechisporales, and Agaricales. The ratio of Basidiomycota was decreased with sole inorganic fertilizer. Moreover, the relative abundance of Zygomycota was increased after 33 years of fertilization, which was dominated by Mortierellales and Basidiobolales at order level. Diversity indices including Shannon, Simpson, Chao1 and ACE were all significantly declined in NPK compared with CK, NPKM and NPKS treatments, whereas Chao1 index and ACE index in NPKM and NPKS were higher than that in CK and NPK. Saprotroph was the main fungal functional group across all the four treatments (48%-57%). Higher proportion of symbiotroph fungi was identified in soils with NPKS and NPKM (17%) in comparison to CK and NPK. The main guilds with the increasing proportion were arbuscular mycorrhizal fungi and ectomycorrhizal fungi. However, significantly higher proportion of animal pathogen fungi were detected in NPK (10%) than other treatments. Redundancy analysis (RDA) showed that moisture, salinity and porosity in soil were more strongly related with fungal community composition and fungal functional composition than soil organic matter and total nitrogen. Our results suggest that sole application of inorganic fertilizer results in great changes in fungal community compositions and the hazard of over production of pathogen fungi, whereas combined organic-inorganic fertilization would be beneficial to maintain the healthy environment through increasing fungal diversity and the ratio of symbiotrophic fungi in yellow clayey paddy soil.

Ecology and trophic links of macroinvertebrates in a dune slack of a Mediterranean coastal ecosystem (Grosseto, Italy)

Along a Tyrrhenian coastal ecosystem the macroinvertebrates of a dune slack were studied to assess food webs, guilds and the possible links with other beach compartments. Environmental monitoring was conducted for an entire year through beach profiling, collection of the vegetation, of substrate samples and of the chemico-physical parameters of the ground water. Macroinvertebrates were assessed seasonally with two line transects of pitfall traps whereas monthly captures were carried out for coleopterans only. Zonations were also calculated to subdivide dune slack residents from non-residents. The plant and invertebrate specie were then grouped using Hierarchical Cluster analysis. Canonical Correspondence Analysis was instead used to evaluate the effect of the environmental parameters of the dune slack on the vegetation structure and macroinvertebrate composition. To evaluate the relative contribution of the different food sources to the diets of the macroinvertebrates a Bayesian stable isotope mixing model was employed. The study clearly showed that the inhabiting dune slack fauna was subdivided in two main guilds of non-predator and predator species and that slacks could be used all year round by resident species adopting particular behaviours or avoiding interspecific competition by modulating their spatial and temporal strategies. Furthermore slacks were exploited as nursery grounds for immature stages of specific species and in other cases as important feeding areas for predators. These findings indicated that macroinvertebrates exploited beach compartments according to the different stages of their life-cycle and that the integrity of the entire beach ecosystem is a key factor to promote a high biodiversity in a sandy beach-dune ecosystem.

Feeding Behavior and Habitat Use in a Waterbird Assemblage at a Marine Wetland in Coastal Patagonia, Argentina

Wetlands are critical foraging areas for many waterbird species, and their relatively high productivity often determines the coexistence of several species using food resources for breeding and/or refueling during migration. Between 18 October and 20 December 2000, we gathered information on foraging habitat use and feeding techniques of sixteen waterbirds during the austral spring at Malaspina inlet, Chubut, Argentina. We quantified the utilization by waterbirds of ten foraging habitat types and seven feeding techniques on seven fixed survey stations along the coastline, representing the different coastal habitats of the Malaspina inlet. The waterbird assemblage was structured in three main guilds: shallow water frequenters (three cormorants, two terns, a grebe, and two steamer-ducks), hard habitat peckers (two gulls, an egret, and an oystercatcher) and soft habitat frequenters (two oystercatchers, a sandpiper, and a duck). These differed greatly in their use of habitats and feeding techniques, suggesting clear differences in the use of food resources. Most of the groups defined used almost exclusively one feeding technique or habitat type. This fact and the low resource utilization breath values suggest the existence of a relatively high degree of specialization within this waterbird assemblage.

Rats on the run: removal of alien terrestrial predators affects bush rat behaviour

Predators can strongly influence the microhabitat use and foraging behaviour of prey. In a large-scale replicated field experiment in East Gippsland, Australia, we tested the effects of reduced alien red fox (Vulpes vulpes) and alien wild dog (Canis lupus familiaris) abundance (treatment) on native bush rat (Rattus fuscipes) behaviour. Bush rats are exposed to two main guilds of predators, namely mammalian carnivores and birds of prey. Tracking rat movements using the spool-and-line technique revealed that, in treatment sites, rats used ground cover, which provides shelter from predators, less often than at unmanipulated fox and wild dog abundance (non-treatment sites). In treatment sites, rats more frequently moved on logs where they would have been exposed to hunting foxes and dogs than in non-treatment sites. Furthermore, in treatments, rats showed a preference for understorey but not in non-treatments. Hence, bush rats adapted their behaviour to removal of alien terrestrial predators. Giving-up densities (GUDs) indicated no treatment effects on the marginal feeding rate of bush rats. Interestingly, GUDs were higher in open patches than in sheltered patches, suggesting higher perceived predation risk of bush rats during foraging at low versus high cover. The lack of treatment effects on GUDs but the clear response of bush rats to cover may be explained by the impact of predators other than foxes and wild dogs.

Temporal coexistence of dung-dweller and soil-digger dung beetles (Coleoptera, Scarabaeoidea) in contrasting Mediterranean habitats

The western part of the Mediterranean basin is a transitional biogeographical region for the distribution of the representatives of the main guilds of dung beetles; towards the south, Aphodiinae (dung-dwellers) become scarce, whereas northwards Scarabaeinae (soil-diggers) progressively disappear. The number of species in local dung beetle assemblages is enhanced by this double faunistic contribution. Annual dung beetle assemblages were sampled in two sub-Mediterranean sites, which differed by 600 m in elevation, in order to determine the phenological dynamics related to the way of using dung (dung-dwellers/Aphodiinae vs. soil-diggers/Scarabaeinae and Geotrupinae). Aphodiids were active all year round, although they were affected by summer drought and, at high elevation, by the length of the cold season. This reduced activity was related to an impoverishment of Aphodiinae and to reduced temporal segregation between species. In contrast, soil-diggers were not active all year round and showed different species assemblages in the two sites. An extension of the activity period of these beetles was observed due to the occurrence of cold resistant species at high elevation. Our results suggested that the occurrence of soil-diggers seemingly did not affect the seasonality of dung-dwellers; their local abundance showed no negative correlation and, most importantly, phenological differences between dung-dwellers were always significantly higher than the seasonal differences between dwellers and diggers.

A numerical classification of reproductive guilds of the freshwater fishes of south‐eastern Australia and their application to river management

AbstractA comprehensive list of freshwater fishes from south‐eastern Australia is classified into five major reproductive guilds, based on numerical analysis of 13 life history or reproductive characteristics. The guilds defined generally support previously proposed, subjective life history‐based classifications of freshwater fish species in this region. The majority of species fell into two groups, with 18 and 19 species, and the remaining guilds each contained from 1 to 12 species. The most important biological characteristics that separated the major groups of species included: care of the eggs or young, the presence of adhesive or non‐adhesive eggs, serial or single spawning, and viviparity. Two of the main guilds could each be divided into two sub‐guilds mainly based upon the requirement for a spawning migration. The objective definition of reproductive guilds allows river and natural resource managers to consider the effects of changes in environmental management on groups of species that are likely to respond in similar ways.

Feeding habits and trophic organization of the fish community in shallow waters of an impacted tropical habitat

The feeding ecology and trophic organization of 32 fish species found in an highly impacted waters from four sites of the eastern Johor Strait, Singapore has been studied. Among the wide variety of prey consumed, calanoid copepod (46.9% domination) was the most important dietary component of fishes in this ecosystem. In general, fishes show a narrow range in adaptive radiation of feeding habits, with only three main guilds identified. Spatially, a more complex guild was recorded for the habitat with more complex structure, although the number of guilds was consistent at three to four guilds. Seasonally, a change of guild organization was observed. Many fish species placed in one guild might be classified in another guild during a different season. This information facilitates the examination of complex associations of fishes and identifies groups of species that use similar resources within a specific community and can serve as a reference for feeding ecology of fishes in highly impacted tropical habitats.

Do Birch Trees (Betula pendula) Grow Better if Foraged by Wood Ants?

1. Populations of insect herbivores in three main guilds were studied on experimental saplings and natural birch (Betula pendula) trees which were either foraged or not foraged by wood ants (Formica rufa) on the Gait Barrows NNR. 2. The effects of the ants on the insects, and hence on the damage by the herbivores to the trees were measured. 3. Growth parameters of foraged and unforaged trees were measured. 4. Of the seven aphid species feeding on Betula pendula, two had mutualistic relationships with the ants and were increased in numbers by them. The remaining five species were decreased in numbers

Spatial and temporal patterns of root activity in a species-rich alluvial grassland.

The time and depth of activity of a number of co-existing grassland plants was measured using a technique involving the simultaneous injection to different depths in soil of 3 chemical tracers - Li, Rb and Sr. Root activity at a particular depth was assessed from the concentration of each tracer in leaf tissue.The seven most constant species showed very similar patterns of root activity, which was greater at 5 than at 15 or 25 cm except towards the end of the growth period in late June. Maximum root activity generally occurred earlier than maximum shoot productivity but there was little evidence of differentiation between species. When root activity was assessed as a proportion of total community root activity, by combining tracer concentration and biomass data, seasonal differences between species were more obvious. Using both root activity and productivity data, species were grouped into two main guilds, one active in spring (April-May) and one in summer (June).Correlations of above-ground biomass with root activity at different depths revealed that species of the spring guild were more active in the 5-15 cm horizons and those of the summer guild at 15-25 cm.These patterns suggest that rooting depth and time of activity are strongly linked: early-active species tend to be less productive and shallower-rooted and this combination of characters allows them to escape from competition with more productive species, by being active at a time when deeper soil layers are less hospitable.

Resource Utilization Pattern and Guild Structure in a Waterfowl Community

Resource utilization and guild structure was studied in a waterfowl community breeding in an eutrophicated lake in SE Finland. The community was composed of 13 species with a density of 123 pairs km-2 and a biomass of 159 kg km-2. Resource utilization was analyzed in terms of feeding habitat and feeding method. Using cluster analysis three and five interpretable main guilds were recognized along these two dimensions, respectively. When the two resource axes were considered simultaneously, the overlaps between the species were usually very low and segregation became more apparent, breaking down the clear one-dimensional guild structure. However, both cluster analysis and the principal component analysis yielded two similar main guilds: diving ducks and grebes; dabbling ducks and coot. In general, the species in the first guild were characterized by wide niche breadths along the feeding habitat dimension and by narrow niche breadths along the feeding method dimension, while among the species in the second guilds the opposite was true. It is suggested that the segregation of the species in the two-dimensional niche space cannot be interpreted as evidence for competition but merely reflects group-specific adaptations to utilize resources intrinsically in different ways. The comparisons between the observed and randomized resource use overlaps using morphologically very similar species pairs did not reflect any strong competitive interactions either. It is concluded that competition does not play an important role in structuring the waterfowl community studied.