Plant damage from and defenses against ‘cryptic’ herbivory: A guild perspective

Abstract

Despite considerable interest in the factors affecting trophic cascades in terrestrial systems, there has been relatively little attention paid to the importance of the herbivore-plant link in explaining why some systems “cascade” (have strong top-down effects on plant survival and population growth) and others “trickle” (have top-down effects on plant damage, but little effect on plant fitness). This is despite the fact that herbivore guild identity has long been recognized as a major force affecting herbivore-plant interactions. We address the potential importance of herbivore guild identity in determining the strength of tritrophic interactions by reviewing literature concerning plant damage from and induced defenses against two “cryptic” herbivore guilds, predispersal seed predators and root/stem borers. Although both guilds are capable of strongly affecting plant fitness, the impact of root/stem borers on plants in natural systems seems far greater than that of predispersal seed predators. The large impact of root/stem borers occurs via their disruption of plant vascular systems, while a variety of factors (safe-site-limited plant populations, long-lived seed banks, temporal plant escape, etc.) each seem important in explaining the smaller effect of predispersal seed predators. While the lack of attention to herbivore guilds is understandable, given the (by necessity) single-species focus of much trophic cascade research, we suggest that predator suppression of root/stem borers and predispersal seed predators will, respectively, yield strong versus weak top-down effects on plant fitness. The potential tritrophic consequences of herbivore feeding mode highlight the importance of research on varied predator-herbivore chains that share a common basal resource.     

Global patterns of guild composition and functional diversity of spiders

The objectives of this work are: (1) to define spider guilds for all extant families worldwide; (2) test if guilds defined at family level are good surrogates of species guilds; (3) compare the taxonomic and guild composition of spider assemblages from different parts of the world; (4) compare the taxonomic and functional diversity of spider assemblages and; (5) relate functional diversity with habitat structure. Data on foraging strategy, prey range, vertical stratification and circadian activity was collected for 108 families. Spider guilds were defined by hierarchical clustering. We searched for inconsistencies between family guild placement and the known guild of each species. Richness and abundance per guild before and after correcting guild placement were compared, as were the proportions of each guild and family between all possible pairs of sites. Functional diversity per site was calculated based on hierarchical clustering. Eight guilds were discriminated: (1) sensing, (2) sheet, (3) space, and (4) orb web weavers; (5) specialists; (6) ambush, (7) ground, and (8) other hunters. Sixteen percent of the species richness corresponding to 11% of all captured individuals was incorrectly attributed to a guild by family surrogacy; however, the correlation of uncorrected vs. corrected guilds was invariably high. The correlation of guild richness or abundances was generally higher than the correlation of family richness or abundances. Functional diversity was not always higher in the tropics than in temperate regions. Families may potentially serve as ecological surrogates for species. Different families may present similar roles in the ecosystems, with replacement of some taxa by other within the same guild. Spiders in tropical regions seem to have higher redundancy of functional roles and/or finer resource partitioning than in temperate regions. Although species and family diversity were higher in the tropics, functional diversity seems to be also influenced by altitude and habitat structure.     

Effects of species vs. functional diversity: Understanding the roles of complementarity and competition on ecosystem function in a tropical stream fish assemblage

The positive effects of biodiversity on the functioning of ecosystems are well demonstrated in laboratory microcosms but the precise mechanisms underlying higher ecosystem process rates in natural assemblages are less well understood. We investigated, under semi-natural conditions (field enclosures), the potentially interactive effects of species identity and trophic function (i.e., feeding guild) on consumer growth, using a fish assemblage in a tropical stream. We tested the relative importance of species identity and trophic function on consumer growth by placing 2 fish of either (i) the same species, (ii) different species but of similar trophic function, or (iii) different species of different trophic functions in each of 72 stream enclosures for 48 days and measuring biomass change, individual diet composition and behavior. We predicted that if functional diversity had a larger impact than species diversity, then fish growth would be highest for pairs of species from different functional groups (i.e., those with the highest diet complementarity), intermediate for different species within a guild, and lowest for the same species (those with the lowest complementarity and highest niche overlap), such that functional variation between species in different guilds would exceed functional differences within guilds. Our results show that functional heterogeneity rather than species diversity per se had the greatest impact on food resources used complementarily, leading to higher biomass accrual. Mechanistically, higher growth rates were driven by concomitant increases in resource intake and reductions in antagonistic interactions. Together, these results underscore the importance of functional diversity on macroconsumer production in natural assemblages.     

On the use of the guild concept in plant ecology

The original definition of the guild is reiterated and the concept discussed and placed in the context of related concepts such as resources and competition. From this conceptual framework the current use of guilds in studies of plant community ecology is evaluated. We discuss the criteria with which species are assigned to guilds, the association of guilds with specific communities, the resource classes on which guilds are based, and the competitive relationships between species of a guild. We conclude that the guild is presently applied in a much more loose way as compared to its original definition. In particular, the a priori assignment of species to guilds on the basis of the use of well-defined resource classes is often relaxed. This obscures the insight that the guild structure may provide in the role of resource partitioning and competition in structuring the community. A more strict use of the concept is advocated.     

Local richness-species pool ratio: A consequence of the species-area relationship

A constant ratio between species richness estimated at the local and regional scale is interpreted as a proof of quasi-neutral unsaturated communities. Based on Zobel’s model of plant community (Zobel,Folia Geobot. 36: 3–8, 2001) we tested the methodology of the species-pool concept by comparing the saturated and unsaturated communities generated by spatially-explicit mechanistic simulations with known assembly rules. Tests show that local-regional species plots can be applied to distinguish saturated vs. unsaturated communities, however, the outcome of tests, i.e. the relationship between local and regional richness depends on the size of the areas compared. Independently from the mechanisms controlling diversity, trivial saturation will appear if one of the scales is either too small or too broad because species-area curves are bound at these extreme scales. Similarly, trivial unsaturaton will appear if the two scales compared are close to each other. The application of species-area curves is useful because they help to find scales for non-trivial relationships. Field tests reporting quasi-neutrality and unsaturated plant communities were performed at the intermediate scales of the corresponding species-area curves, and they were estimated from heterogeneous samples. Therefore, this field evidence might be biased by scaling artefacts. We propose to reanalyze the field evidence with solid scaling conventions and to restrict the concept of quasi-neutrality to subordinated functional groups based on the following hypotheses: (1) neutrality will appear within subordinated guilds as a consequence of the hierarchical structure of plant communities; (2) the lower a guild in the hierarchy the higher neutrality of within-layer processes detected; (3) quasi-neutrality found at the community level is not a proof of community-level neutrality but it is due to the higher number of subordinated species in the samples.     

Guild structures of seed insects in relation to acorn development in two oak species

We investigated patterns of acorn growth in Quercus variabilis Blume and Quercus serrata Thunb., seasonal trends in emergence of seed insects found in the acorns, oviposition periods of the insects and falling periods of insect-infested acorns. In Q. variabilis, two insect guilds were associated with acorn development: (i) the immature acorn feeding (IAF) guild [Curculionidae sp., Poecilips cardamomi (Schaufuss), and Characoma ruficirra (Hampson)]; and (ii) the mature acorn feeding (MAF) guild [Curculio robustus (Roelofs), Curculio sikkimensis (Heller), and Cydia glandicolana (Danilevsky)]. In Q. serrata, there were three guilds: (i) the pistillate flower feeding (PFF) guild (cynipid wasp); (ii) the IAF guild [sap absorption by Mechoris ursulus (Roelofs)]; and (iii) the MAF guild (M. ursulus, C. sikkimensis, Cydia danilevskyi (Kuznetzov), C. glandicolana and Autostichidae sp.). The succession of guilds during acorn development may be a consequence of the use by different species of the limited food resource. The lack of a PFF guild in Q. variabilis that was found in our field site would have a positive effect on IAF guilds in utilizing the acorns.     

A partial food web involving predatory gastropods on a Pacific fringing reef

An analysis of the feeding habits of a diverse assemblage of predatory gastropods on a Guam fringing reef, shows that seven major prey categories are eaten, namely polychaetes, sipunculans, gastropods, bivalves, crustaceans, ophiuroids, and fish. The three largest feeding groups are the polychaete feeding guild which mainly consists of species of Conus, the gastropod guild dominated by species of the Muricidae and the sipunculan guild consisting mainly of the Mitridae. There is considerable dietary overlap between members of feeding guilds, but interaction between guilds is low and accounted for by the relatively few generalist species in the community.     

Predicting resilience of ecosystem functioning from co‐varying species' responses to environmental change

Understanding how environmental change affects ecosystem function delivery is of primary importance for fundamental and applied ecology. Current approaches focus on single environmental driver effects on communities, mediated by individual response traits. Data limitations present constraints in scaling up this approach to predict the impacts of multivariate environmental change on ecosystem functioning. We present a more holistic approach to determine ecosystem function resilience, using long‐term monitoring data to analyze the aggregate impact of multiple historic environmental drivers on species' population dynamics. By assessing covariation in population dynamics between pairs of species, we identify which species respond most synchronously to environmental change and allocate species into “response guilds.” We then use “production functions” combining trait data to estimate the relative roles of species to ecosystem functions. We quantify the correlation between response guilds and production functions, assessing the resilience of ecosystem functioning to environmental change, with asynchronous dynamics of species in the same functional guild expected to lead to more stable ecosystem functioning. Testing this method using data for butterflies collected over four decades in the United Kingdom, we find three ecosystem functions (resource provisioning, wildflower pollination, and aesthetic cultural value) appear relatively robust, with functionally important species dispersed across response guilds, suggesting more stable ecosystem functioning. Additionally, by relating genetic distances to response guilds we assess the heritability of responses to environmental change. Our results suggest it may be feasible to infer population responses of butterflies to environmental change based on phylogeny—a useful insight for conservation management of rare species with limited population monitoring data. Our approach holds promise for overcoming the impasse in predicting the responses of ecosystem functions to environmental change. Quantifying co‐varying species' responses to multivariate environmental change should enable us to significantly advance our predictions of ecosystem function resilience and enable proactive ecosystem management.     

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.     

Indicator guilds representing forest composition and configuration in the Great Lakes – St. Lawrence forest region – A nationally replicable selection methodology

Sustainable forest management (SFM), an explicit policy objective in Canada, balances social, economic and environmental values. The status and trends of forest-associated species is one indicator of SFM, though it is under utilized due to challenges with indicator selection and data availability. This paper demonstrates and tests an indicator selection methodology which combines Breeding Bird Survey (BBS) data and LandSat land cover data to identify indicator guilds, or groups of indicator species, for a series of forest composition and configuration attributes in the Great Lakes St. Lawrence forest region. Guild performance is tested at independent sites within the region and compared with that of guilds assembled using known species’ habitat preferences, and abundance trends are reported for two periods: 1990–2007 and 1967–2007. Guilds assembled using the method proposed here describe more variation in forest composition (r-sq(adj): 41–76) than those assembled using known habitat preferences alone (r-sq(adj): 17–58). Forest configuration guilds, which were not compared with existing guilds, also describe a large proportion of variation in configuration attributes (r-sq(adj): 47–76). Guild abundance remained stable over the long and short term for most guilds with the exception of the wetland guild, which increased moderately over the long-term, and the deciduous guild which increased moderately over the short-term. Despite challenges associated with the use of bird guilds as indicators of forest composition and configuration, results presented here suggest that indicator guilds may provide useful information regarding the status and trends of regional scale forest composition and configuration attributes.     

Obituaries

Abstract

It has been suggested that bryophyte communities differ from those of higher plants, in that species coexistence is not limited by inter-specific competition. To test this hypothesis, bryophyte ‘lawns’ were-sampled at six locations in southern New Zealand. At each site, 625 quadrats, each ca 1 X 1cm, were arranged on a contiguous grid.

Variance in quadrat richness was significantly less than expected on a random basis at four sites, with the same trend in a fifth, i.e. quadrat richness was relatively constant. Since a patch model was used to reduce the effects of micro-environmental variation and spatial autocorrelation, this suggests that competition was restricting coexistence. The degree of restriction was similar to that found previously in grass lawn communities.

Species association was calculated on a patch basis, examining only small spatial-scale deviations from expectations. At four- sites this gave only negative associations. At the other two sites there were both positive and negative associations, but the pattern of associations gave no indication of Root/Pianka-type guilds.

Examination of the variance in guild proportions, using taxonomic (moss vs liverwort) and morphological (prostrate vs erect) guilds, gave- no indication of significant guild structure for any site (i.e. in the overall analyses for each site, index RV_gp was very close to the null-model expectation of 1.0).

Searches using the Wilson- Roxburgh method failed to reveal any significant intrinsic guild classification. That is, there was no indication of groups of species within a community that tended to be mutually exclusive because of similarity in resource use. Thus, lack of guild proportionality using a priori guilds was not due to the use of an inappropriate guild classification, but to lack of a guild structure in the communities.

It is concluded that there is community structure among bryophytes, in that species exclude each other to the same degree as higher-plants do in their communities. However, there is no evidence of structuring of these bryophyte communities into guilds; it seems that bryophyte species all form one guild.     

Oribatid mites reveal that competition for resources and trophic structure combine to regulate the assembly of diverse soil animal communities

相似文献   

Patterns of morphological traits shaping the feeding guilds in the intertidal mudflat fishes of the Indian Sundarbans

Broad-scale patterns of resource utilization and the corresponding morphological evolution is a result of an integral relationship among form and function. In addition, there is also an inherent role of the latter in determining species co-interaction and assemblage pattern that forms an integral aspect of ecological research. The present study aimed to evaluate the ecomorphological relationship among 37 fish species inhabiting the intertidal mudflats of the Indian Sundarbans by outlining the following objectives: (i) identifying and characterizing feeding guilds/groups and (ii) understanding the inter-relationship between morphometry with (a) the established feeding guild classifications and (b) observed prey taxa (that characterizes these feeding groups) for determining the role of morphometry in prey acquisition followed by (iii) the evaluation of their potential phylogenetic convergence among the species. For the first objective, two approaches for feeding guild classification were made (3-Guild and 8-Guild) for assessing the prediction accuracy of morphological characters in identifying the different guilds. While the former was based on troph values, the latter classification mode relied on the similarities in diet composition among the different fish species. For addressing the second objective, we employed two different models namely, linear discriminant (LDA) and redundancy analysis (RDA). While the LDA model tested the prediction accuracy of morphological traits in classifying the different feeding guilds, RDA was applied to model the correlation between the morphological traits and the prey categories. In the LDA model, morphological characters showed higher accuracy (78.4%) in classifying three feeding groups rather than eight feeding groups (73%). Following this, the RDA model (explaining 79.78% of constrained variance) showed gill raker intensity, protrusion length, head depth, caudal peduncle, eye diameter and inter-orbital distance to be highly associated with selection of specific prey types by species, thereby characterizing a particular feeding guild. However, generalized linear models testing for correlation between troph value and feeding groups showed substantial variation (90.35%) in the dietary index being explained by the 8-Guild classification. Hence, our study maintains the assumption that broad morphological differentiation acts as one of the underlying processes resulting in dietary variations that results in the varying modes of resource utilization by the coexisting species, thereby determining the structure of a trophic guild. Furthermore, it also suggests that in terms of prey abundance or selectivity, the 8-Guild model is much more conducive in representing the feeding habits of the species while the morphological traits reflected a relatively broader scheme of classification, (i.e., 3-Guild model) with certain traits being phylogenetically conserved within these groups.     

莱州湾鱼类群落同功能种团的季节变化

利用2011年5月、8月、10月和12月底拖网调查数据,对莱州湾海域鱼类同功能种团特征及其季节变化进行了研究。全年调查共渔获鱼类49种,全部为硬骨鱼类。根据鱼类的摄食习性,调查海域鱼类可划分为浮游动物食性种团、浮游动物/底栖动物食性种团、底栖动物食性种团、底栖动物/游泳动物食性种团、游泳动物食性种团、杂食性种团和碎屑食性种团共7个同功能种团,其中底栖动物食性种团种类数最多(14种),底栖动物/游泳动物食性种团次之(12种)。碎屑食性种团生物量在全年处于第一优势地位,占32.8%;其次为浮游动物食性种团,占31.6%;再次为底栖动物/游泳动物食性种团,占25.0%。同功能种团多样性(HFD)和种类多样性(Hs)季节变化趋势相同,均在夏季达到最高值,冬季达到最低值;两者关系使用指数方程拟合效果最佳。浮游动物食性种团平均营养级为3.71、浮游动物/底栖动物食性种团为3.83、底栖动物食性种团为3.43、底栖动物/游泳动物食性种团为3.75、游泳动物食性种团为3.86、杂食性种团为3.73、碎屑食性种团为3.34。与20世纪80年代、90年代调查结果相比,目前莱州湾碎屑食性种团比例明显上升,游泳动物食性种团比例大幅下;底栖动物食性种团和游泳动物食性种团的平均营养级明显下降,碎屑食性种团平均营养级有所上升。     

Inter- and intra-guild patterns of food resource utilization by chironomid larvae in a subtropical coastal lagoon

Studies on food preferences provide background information on the mechanisms that allow coexistence and resource exploitation among several species within the same system. In this study, we aimed to identify the trophic guild of chironomid larvae based on their feeding habits using gut content analysis. Larvae were collected using an Eckman-Birge grab in many areas of the subtropical Peri lagoon (southern Brazil) seasonally between March 2008 and April 2009. Null models were used to determine the frequency of co-occurrence of food items in the diets of chironomid larvae and to determine the frequency of co-occurrence of species belonging to a particular guild. Significant differences (seasonal or annual) were observed in patterns of co-occurrence of food items in the larval diets. Animal remains had a lower co-occurrence than would be expected as a result of chance, and plant items had a co-occurrence greater than would be expected by chance. The c scores for co-occurrence of species belonging to both predator and herbivore guilds revealed a higher co-occurrence of species than would be expected by chance. We suggest that the factors responsible for the results of this study were resource partitioning among species, habitat heterogeneity and resource availability in the environment.     

千岛湖陆桥岛屿鸟类集团对栖息地片段化的敏感性及其季节变化

为探究千岛湖陆桥岛屿不同鸟类集团对栖息地片段化敏感性的差异和季节变化,于2009年4月—2012年1月鸟类繁殖季(4、5、6月)和冬季(11、12、1月)对千岛湖41个陆桥岛屿鸟类集团进行了研究。结果表明,冬季杂食鸟对片段化敏感性高于食虫鸟,繁殖季时二者无显著差异,繁殖季和冬季时下层鸟对片段化敏感性均高于林冠鸟,冬季留鸟对片段化敏感性高于候鸟,繁殖季则无显著差异。杂食鸟和留鸟对片段化敏感性存在季节差异,而食虫鸟、林冠鸟、下层鸟和候鸟对片段化敏感性均无季节差异。不同鸟类集团对栖息地片段化敏感性的差异和季节变化规律,有助于人们在栖息地管理和保护区设计时采取更有针对性的鸟类保护措施。     

Associations between avian functional guild response and regional landscape properties for conservation planning

This project facilitates a regional approach to conservation planning in Pennsylvania based on avian breeding habitat selection. The objectives were to: (1) determine the sensitivity of spatial pattern in avian diversity to changing thresholds of intra-guild species richness and (2) relate change of spatial pattern in avian diversity with landscape characteristics of bird Atlas blocks. Two state-wide spatial data layers, based on Landsat satellite data were constructed for this study. These regional landscape data were compared to Breeding Bird Atlas data from 1983 to 1989 using a geographic information system. Breeding bird data were recorded from 4928 blocks that form a grid covering Pennsylvania. Correlation analysis reduced landscape variables to 12 originally derived from forest, urban, roads, streams, and topographic data.Avian functional response guilds were used to analyze associations between breeding bird data and landscape variables. Functional response guilds were created by grouping organisms based on shared habitat preferences or behavioral characteristics. Most of the 18 avian guilds identified for this study were based on shared structural resource characteristics of preferred breeding habitat. Preferred structural resources frequently included the amount and type of forest. For this study, guilds separate resource characteristics by: (1) primary habitat (i.e. forest interior, forest edge), (2) area sensitivity (i.e. forest and grassland), (3) migratory status (i.e. resident, temperate, and tropical), and (4) nest placement (i.e. canopy nester, forest ground nester). Wetland obligate species were treated as a separate guild. Breeding Bird Atlas blocks were tabulated with respect to the number of species present from each guild. For a given guild, the number of its species in a block is termed guild-specific species richness. Sample blocks having high species richness for a given guild often occur adjacent or in close proximity forming spatial clusters in the landscape. Spatial coherence (adjacency/proximity) among the blocks forming these islands is shared guild-specific richness. Spatial clustered blocks of each guild represent areas that presumably possess required resources for members of that guild. Blocks having high intra-guild richness were evaluated with a group of block-level continuous variables using multiple logistic regressions. Logistic regression results indicate that a convincing connection exists between landscape properties of Breeding Bird Atlas blocks and habitat selection characteristics of guild members. Percent of forest cover and mean elevation were the most important habitat characteristics influencing intra-guild richness for most of the guilds tested. Concordance values from logistic regression were used to determine the strength of each guild model. Concordance, the proportion that represents the percent of correct guild richness predictions versus incorrect predictions, suggests a relationship between guild-rich clusters and habitat resources required by each guild. The highest concordance was for the exotics guild at 76.3% and the next highest was 74.8% for the grassland area sensitive guild. This signifies a 75% certainty that landscape variables could predict occurrence of a guild-rich block. Eight more guilds had concordance values greater than 65%.By using a guild approach, this study goes beyond total diversity to the more informative structural and functional diversity of guilds. Spatially clustered blocks of high species richness for a particular guild are more indicative of habitat availability and quality than would be the case for overall species richness. Clusters of blocks having high intra-guild species richness become candidate areas for conservation efforts.     

Niches and size relationships in Coleoptera associated with Cardueae host plants: adaptations to resource gradients

Summary The ecological meaning of size relationships within guilds is still a matter of debate. We analyzed the niches and size relationships in Coleoptera associated with Cardueae host plants. Species were grouped into guilds using distributional data, host records and feeding strategies: a) The species of the genus Larinus are inhabitants of flower heads within the Cynaroideae. Two types of Larinus species were distinguished: one type attacks immature flower heads, the other exploits the floer heads in a more advanced stage. The females of the first group have elongated rostres adapted to piercing through the bracts of closed flower heads, the other group possesses blunt, short rostres. For an oligophagous group of four Larinus species we are able to show that the distribution of average female rostre length is non-random. b) In southern France four stem boring species of the genera Agapanthia and Lixus coexist within the same hosts. The frequency distributions of body length from these species are clearly overdispersed. c) Coexisting species of the folivorous genus Cassida show no differences in body sizes. We conclude that morphometric differences within the investigated guild of endophytic species (Larinus and Agapanthia/Lixus) evolved in response to size of the used plant structures and the size of potentially competing species, a pattern not evident in ectophytic species. We suggest that these differences are part of a general pattern as the evolution of herbivorous guild may strongly depend on the way how the host resource is exploited (endophagy vs ectophagy). So current differences in statements on the organization of herbivore communities could perhaps be reconciled.     

Variability in species richness and guild structure in two species-rich grasslands

It has been suggested that variation in the proportion of species in guilds (=guild proportionality) indicates community structuring by guilds in biotic communities. This hypothesis was tested on a subthermophilous grassland and a mesotrophic meadow at a scale of 0.09 m² based on a five-year data set. Further, variation in the total number of species, variation in the number of species belonging to a guild and non-randomness in species composition of guilds were studied. A number of criteria for guild definition were used, such as life form, Grime's C-S-R strategy, phenology, plant height, pollination and dispersal syndromes, leaf shape and anatomy and taxonomy at the family level. The observed variation in the number of guild species corresponded to the null model in which species assemblages with fixed species richness per square were randomly generated from the species pool. The observed variation in the number of guild species was often higher than the variation calculated for randomly distributed species whereas the variation in the proportion of guild species was in some cases lower than the variation calculated for randomly distributed species with fixed frequencies. Possible reasons for the discrepancy in the results based on different models are discussed. It is concluded that there is little evidence of guilds in the organization of grasslands. *** DIRECT SUPPORT *** A02DO006 00012     

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.