Effects of Chiton granosus (Frembly, 1827) and other molluscan grazers on algal succession in wave exposed mid-intertidal rocky shores of central Chile

Molluscan grazers can have important effects on the abundance, colonization rates, and successional pathways of algal assemblages and the entire intertidal community. In general, early successional algae are more readily consumed than corticated algae and kelps, which usually get established later in the community succession. To generalize, however, the effect of different grazers on algal assemblages must be examined on different coasts and under different scenarios. This information could help us understand the mechanisms of ecosystem processes and situations in which general models do not apply. Along the coast of Chile, humans harvest large keyhole limpets, which seem to be the only invertebrate grazers capable of controlling the dominant corticated alga Mazzaella laminarioides, a canopy-forming species that can cover extensive areas of the mid intertidal zone. In this scenario, where large limpets are harvested, the overall effects of the diverse molluscan assemblage of limpets, chitons and snails on algal succession and on corticated algae in particular are not clear. We conducted a 26-month-long experiment to evaluate the effects of molluscan grazers on mid-intertidal algal succession and to isolate the effects of Chiton granosus, the most conspicuous member of the assemblage at these tidal elevations. At sites heavily impacted by humans the molluscan grazer assemblage had strong negative effects on colonization and abundance of green algae such as ulvoids and Blidingia minima. In doing so, the grazer assemblage had a strong negative indirect effect on the establishments of chironomid fly larvae, which were only observed on green algal mats and rarely on bare rock. No significant effects were detected on epilithic microalgae, and effects on sessile invertebrates were highly variable over space and time. C. granosus also had significant negative effects on green algae but did not account for the total grazing pressure exerted by the guild. Limited foraging excursions (ca. 35 cm) from refuges and moderate site (crevice) fidelity in this species may contribute to the patchiness in green algal distribution observed in the field. Nearly 13 months after rock surface were experimentally cleared, M. laminarioides appeared in all experimental plots, but increased over three times faster in enclosures containing C. granosus than in exclosures plots or controls, suggesting that moderate levels of herbivory could actually facilitate the establishment of this alga in the succession and that the green algal cover found in the absence of grazers may delay its establishment.     

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.     

The influence of coastal upwelling on the functional structure of rocky intertidal communities

Summary Relationships between organisms at all trophic levels are influenced by the primary productivity of the ecosystem, and factors which enhance rates of primary production may modify trophic relationships and community structure. Nutrient enrichment of intertidal and nearshore waters leads to enhanced production by intertidal algae, and it was hypothesized that where rocky shores are washed by nutrient-rich upwelled waters, the intertidal communities should show a characteristic functional structure, based on the effects of enhanced primary production. Study sites were chosen on rocky shores in southern Africa, central Chile and the Canary Islands, in areas with and without coastal upwelling, and mid-shore community structure at these sites was analysed in terms of the abundance of certain functional guilds of organisms.It was found that algal cover and the biomass of herbivorous limpets supported per unit area on rocky shores were significantly greater in regions of coastal upwelling than in regions where upwelling did not occur. Ground cover by sessile filter-feeding organisms was significantly greater on shores in non-upwelled areas. However, correspondence analysis showed no functional aspect of intertidal community structure that was characteristic of coasts washed by upwelled waters. Primary reasons for this are probably the large variations in the nature of nutrient enrichment that accompanies upwelling, and in the nutrient status of non-upwelled areas. Other factors are man's exploitation of intertidal organisms and differences in the genetic origins of the intertidal species involved.     

The relationship of bionts and taphonomic processes in molluscan taphofacies formation on the continental shelf and slope: eight-year trends: Gulf of Mexico and Bahamas

The Shelf and Slope Experimental Taphonomy Initiative (SSETI) deployed a suite of molluscan species in environments covering a range of depths and sediment types in the Bahamas and on the Gulf of Mexico continental shelf and upper slope for 8 years. Taphonomic state rarely correlated with the distribution of biont guilds among environments. The preservable and nonpreservable biont guilds were also routinely orthogonal. Several coincidences of taphonomic trait and biont guild occurred, including green discoloration that consistently co-occurred with boring algae and bacterial films associated with the development of chalkiness and a soft shell surface. Environments of preservation (EOPs) of disparate taphonomic signature and biont guild complement occur in similar sediment types and environments with similar rates of burial. A paucity of biont coverage is no more a reliable indicator of rapid burial than is a limited degree of shell degradation. The suggestion that preservable bionts might protect shells from taphonomic processes is not well supported. Certain EOP groups are delineated from others most readily by a combination of biont guild and taphonomic trait. Thus, biont guilds augment taphonomic analysis in differentiating EOPs. Shell preservational state, including taphonomic signature and biont coverage, is influenced in a complex way by environment. The analysis confirms an expectation that the diversity of EOPs should be greater in shallow water. Clustering of EOPs reveals that visually distinctive environments may be taphonomically and biotically similar. Visually similar environments may be quite disparate in taphonomic state and biont complement. EOPs grouped by similarity in taphonomic signature and biont coverage very likely define geographically widespread biological and taphonomic regimes, which, however, are everywhere restricted locally in areal dimension.     

Insect guild structure associated with eastern hemlock in the southern Appalachians

An assessment of the insect guild structure associated with immature and mature eastern hemlock, Tsuga canadensis (L.) Carrière, at high and low elevations was made before the invasion by the hemlock woolly adelgid, Adelges tsugae (Annand), and elongate hemlock scale, Fiorinia externa Ferris. Guild dynamics were determined among 243 insect species associated with eastern hemlock in the southern Appalachians. Detritivore, hematophage, herbivore, fungivore, parasitoid, predator, scavenger, and transient guild assignments were made. The herbivore and transient guilds were subdivided into chewers, sapsuckers, flower feeders, pollen feeders, pollen/nectar/sap feeders, and seed feeders. A significant association was found between guilds on immature and mature hemlocks at low elevations, but no significant association was found at high elevations. There was also a strong association of phytophagous insects on immature hemlocks and scavengers on mature hemlocks. The observed transient, scavenger, and predator guilds had a significantly lower co-occurrence among species indicating segregation of the species within these guilds. The herbivore guild had a significantly higher co-occurrence among species than the simulated index indicating aggregation of species within this guild across sites. Detritivore, hematophage, and parasitoid guilds did not differ significantly from the simulated community. These results document a diverse and dynamic insect community on eastern hemlock before invasion by hemlock woolly adelgid and elongate hemlock scale.     

The effects of tidal height,wave-exposure,seasonality and rock-pools on grazing and the distribution of intertidal macroalgae in New South Wales

The effects of grazers (mostly gastropods), height on the shore, wave-exposure, season of the year and the presence of shallow rock-pools on the abundance of intertidal macroalgae were examined on shores at Cape Banks (Botany Bay). At the beginning of each of the four seasons, experimental plots with and without grazers were cleared at four heights on three shores, of increasing exposure to waves, The colonization and growth of algae in these plots were monitored (by measurement of per cent cover and dry wt) for approximately the next 3 months in each season.In grazed plots, foliose algae only grew at the lowest levels on the shores. They were more abundant where wave-action was greater, and during the cooler periods of the year, when growth of the plants was enhanced. Higher on the shore, there was a positive correlation between algal cover in grazed plots and the amount of rainfall during the previous 10 days. In all seasons, there was much greater colonization of foliose algae where grazers were excluded. There was greater algal growth at lower levels on the shore, and where wave-action was stronger. Less algae grew in sheltered areas during warmer times of the year. The major seasonal difference found was the more rapid growth and occupancy of the rock by algae during the cooler seasons of the year.Experimental rock-pools were colonized more rapidly at lower levels on the shore, and during the winter. There was no difference between pools and control (non-pool) areas during winter. During summer, however, there was a greater per cent cover and biomass of algae in pools from which grazers had been excluded than in similar control areas.The results can be interpreted as being due to the greater survival and more rapid growth of algae under conditions of increased moisture, decreased emersion and decreased temperatures and light regimes during low tide (i.e. when physical stresses were reduced). These physical factors were, however, less important to the distribution of the algae than were the effects of grazers. Although few algae were present in any experimental plot, the number of species of algae per plot was considerably reduced in grazed areas.The results confirm that the patterns of vertical distribution and abundance of algae on rock-platforms in New South Wales are primarily the result of the activities of grazers. All algae in the present study were capable of living higher on the shore than they were normally found. Much of the variation along a gradient of wave-exposure, from season to season, and small-scale variation from place to place at any time can be explained by the complex interactions between the activities of grazers, and the effects of variations in the physical environment that influence the recruitment, survival and growth of the algae.     

Comparative trophic morphology in eight species of damselfishes (Pomacentridae)

Damselfishes show significant biodiversity in the coral reefs. To better understand such diversity, an ecomorphological approach was investigated in the trophic morphology of eight species of Pomacentridae (Chromis acares, C. margaritifer, Dascyllus aruanus, D. flavicaudus, Pomacentrus pavo, Plectroglyphidodon johnstonianus, Pl. lacrymatus and Stegastes nigricans) belonging to different trophic guilds (zooplankton, algal, coral polyp feeders and omnivores). Geometric morphometrics were used to quantify size and shape variations in four skeletal units: (1) neurocranium, (2) suspensorium and opercle, (3) mandible and (4) premaxilla. This method allowed us to reveal shape and size differences correlated to functional diversity both within and between trophic guilds. Among zooplanktivores, C. margaritifer, D. aruanus and D. flavicaudus have a high and long supraoccipital crest, short mandibles forming a small mouth and high suspensoria and opercles. These three species can be considered to be suction feeders. In the same guild, C. acares shows opposite characteristics (long and thin mandibles, lengthened neurocranium and suspensorium) and can be considered as a ram feeder. Among herbivores and corallivores, the two species of Plectroglyphidodon and S. nigricans can be considered as grazers. Differences in skeletal shape are mainly related to improving the robustness of some skeletal parts (broad hyomandibular, short and high mandibles). The shapes of P. pavo, which feeds largely on algae, strongly differ from that of the other three grazers exhibiting similar morphological characteristics to C. acares (e.g., long and shallow suspensorium, lengthened neurocranium). This highlights likely differences concerning cutting or scraping method. Finally, no strong correlations exist between size and shapes in the eight studied species. Size difference among species having a very similar shape could be viewed as a factor optimizing resource partitioning.     

Algae-associated marine molluscs in the Azores

The raolluscan fauna of a special habitat, the high intertidal algal turf, was studied at four stations on the island of Sao Miguel, Azores. The number of species found ranged from 13 to 23. However, a small group of only six species (the bivalve Lasaea adansoni and the gastropods Pisinna punctulum, Omalogyra atomus, Fossarus ambiguus, Skeneopsis planorbis and Alvania postrema) accounted for more than 80% of all the specimens collected. Mollusc density reached values of 20000 specimens per 100 g algal dry weight. The abundance and number of species of molluscs was comparable with those reported for algal zones lower on the Azorean shores.
Wave exposure and seasonality effects were found to be small, presumably because of the relatively mild abiotic conditions and the protective role of the turf. The algal substrata influenced the phytal molluscan community in two ways. First, the abundance of molluscs was significantly correlated with algal dry weight. Secondly, molluscan abundance and diversity were influenced by the algal composition of the turf. A rich algal composition, with several species of branched fleshy and coralline algae, was associated with a rich molluscan fauna. The dominance of coralline algae resulted in a abundant but species-poor fauna, while an almost monospecific turf of Gigartina was poor in both species and number of molluscan fauna.     

Evaluating the role of biotic interactions in structuring communities using a gradient analysis of multiple interacting guilds

The extent to which ecological communities are coherent entities as opposed to mere intersections of individual species distributions has long been one of the fundamental questions of ecology. Gradient analysis is one commonly used tool for addressing this question; however, all such studies have used organisms from a single taxon or guild. This risks missing important connections due to non‐competitive interactions, which should be more likely to occur between members of different guilds. Such organisms are unlikely to compete for resources and can have complementary niches that promote non‐competitive interactions. We examined the abundances of taxa in four interacting guilds along an elevation gradient in a forest in the southern Appalachian mountains. A causal discovery algorithm was used to investigate the relative frequencies of interguild and intraguild interactions. These were approximately equally common once taxonomic richness was taken into account. We used elements of metacommunity structure analysis to study the extent to which species distributions are non‐independent and tested the hypothesis that combinations of two or more interacting guilds exhibit more coherence than single guilds. In this analysis, all guilds other than collembola were classified as Clementsian or quasi‐Clementsian. (Collembola were classified as random.) When sets of multiple guilds were examined, Clementsian and quasi‐Clementsian structures predominated. We also compared boundary conjunction, measured as Morisita’s index (MI) for these sets of guilds to the weighted average of the guilds’ MI values. Only sets of directly interacting guilds had higher‐than‐baseline boundary conjunction values, and such boundary conjunction values are found in all but one set of directly interacting guilds. Our results highlight the importance of inter‐guild interactions in structuring patterns of cooccurrence. Trophic interactions and plant–fungus symbioses (mutualistic and/or pathogen–host) appear particularly important.     

Feeding guilds and food resource partitioning in a lake fish assemblage: an ontogenetic approach

Ontogenetic diet patterns and trophic guild structure of a 15 species temperate lake fish assemblage were analysed over wide size intervals (up to seven orders of magnitude in body mass), representing practically the whole life span in most species. A two-step objective clustering technique supplemented with other multivariate statistical tools proved that size-related diet changes clearly played an important role in structuring trophic organization of fishes inhabiting Lake Balaton. As many as 13 out of the 15 fish species showed marked size-related dietary changes with two to four ontogenetic feeding stages. At the assemblage level, 11 trophic guilds were separated. Guild membership was size-dependent in 11 fish species that participated in two to four trophic guilds during their life span. The most complex trophic ontogeny was observed in roach Rutilus rutilus and asp Aspius aspius with four guild memberships. This study showed that trophic status of fishes may be very size-sensitive and thus a universal classification of fish species to general trophic guilds, such as 'planktivore', 'benthivore', 'piscivore' or 'herbivore', should be applied very carefully even in environmental monitoring and fisheries management applications, unless it is supported by relevant results of life span diet analyses.     

Effect of siltation on stream fish communities

Synopsis The effect of siltation on stream fish in northeast Missouri was evaluated using community structural measurements and a functional approach that emphasized feeding and reproductive guilds. As the percentage of fine substrate increased, the distinction among riffle, run, and pool communities decreased, primarily because the number of individuals of typical riffle species decreased. Within the riffle communities the abundance of fish of two feeding guilds — benthic insectivores and herbivores — was reduced as the percent of fine substrate increased. The abundance of fish in other feeding guilds was not affected. The only reproductive guild to be similarly affected was the simple and lithophilous, whose members require a clean gravel substrate for spawning. Species within each guild affected by siltation had significantly similar trends in abundance. The guild analysis indicated that species with similar ecological requirements had a common response to habitat degradation by siltation.     

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     

Large scale patterns and trophic structure of southern African rocky shores: the roles of geographic variation and wave exposure

In this study we revise the biogeographic delimitation, and large-scale patterns of community structure of the intertidal rocky shores of southern Africa. We use binary (presence/absence) and per-species biomass data collected at fifteen localities and thirty-seven different rocky sites, encompassing the shores of southern Namibia, South Africa and southern Mozambique. Multivariate analyses revealed that the shores of southern Africa (south of 25°) can be divided into three main biogeographic provinces: the west coast or Namaqua province, the south coast or Agulhas province and the east coast or Natal province. The biomass structure of the intertidal rocky shores communities of southern Africa varied at a large scale, corresponding to biogeographic differences, while local-scale variation accorded with the intensity of local wave action. The average biomass of west coast communities was on average significantly greater than that of the south and east provinces. At a local scale, the community biomass on exposed shores was an order of magnitude greater than on sheltered shores, within all biogeographic provinces. Semi-exposed shores exhibited intermediate average biomass. The trophic structure of these communities varied significantly with wave action: autotrophs, filter-feeders and invertebrate predators were more prevalent on wave exposed than sheltered shores, whereas grazers were more abundant on sheltered and semi-exposed shores. Exposed shores were consistently dominated by far fewer species than semi-exposed and sheltered shores, independently of biogeographic differences. Within all biogeographic provinces semi-exposed and sheltered shores were more diverse than exposed shores. West coast intertidal communities therefore had high levels of biomass, but were consistently species-poor. Several working hypotheses that could explain these large and small-scale patterns are presented.     

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.     

Diatom ecological guilds display distinct and predictable behavior along nutrient and disturbance gradients in running waters

Three diatom ecological guilds were distinguished based on their potential to tolerate nutrient limitation and physical disturbance, i.e. a low profile, high profile, and motile guild. The guild distributions were examined along nutrient and flow disturbance gradients and across habitats in two extensively sampled streams. The guilds showed distinct distributional patterns, i.e. the low profile guild was favored in nutrient-poor and high disturbance habitats; the high profile guild reached a maximum in nutrient-rich sites and in conditions of low flow disturbance; and the motile guild increased along the nutrient gradients and decreased along the disturbance gradient. Guild distribution was habitat-specific: the low profile guild dominated the epipsammon, the high profile guild showed preference for epilithon and epiphyton, and the motile guild—for epipelon. The highest guild diversity was observed at high nutrient levels across all habitats, at higher flow disturbance levels, and in the epipelon and epiphyton. Comparisons of species, guild, and environmental distances, derived from species counts, guild abundance, and physico-chemical data, respectively, revealed high congruence between species–environment and guild–environment correlations. The predictable behavior of the three ecological guilds along nutrient and disturbance gradients, and across major benthic habitats elucidates the functional value of different diatom growth morphologies in species–environment interactions and suggests a potential use in ecological assessments of human-impacted ecosystems.     

Guild structure of arthropods from Bornean rain forest trees

ABSTRACT. 1. 23275 arthropods collected by insecticide fogging from ten Bornean lowland rain forest trees were sorted to approximately 3000 species and assigned to guilds using two sets of criteria.
2. The rank order for proportions of guilds of species but not individuals is similar in tropical and temperate canopy samples.
3. Misplacement in the guild assignments of a few species can cause important differences in the proportions of certain guilds. This can seriously affect the results of comparisons of different samples, and views on proportional constancy of guilds of species on different trees.
4. Guilds of arthropod species such as chewers, suckers, all phytophages, predators, ants and tourists, occur in constant proportions in samples from different tropical trees and this constancy of proportion is similar in samples from groups of'closely related'and'distantly related'trees.
5. The guild concept of community structure and problems in assigning species to guilds are considered with respect to arthropod samples. The conclusions on constancy of proportion for guilds of species are tempered by remarks on the problems of guild composition.     

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.     

Biodiversity of soil microarthropods: the filtering of species

Decline of soil microarthropod biodiversity is described in the sequence: old forest stands, low-input grasslands, high-input grasslands (with and without the use of persistent pesticides). With this expected trend of declining biodiversity, the patterns of species losses are analysed with the use of classifications of life-history tactics, feeding guilds and tolerances to drought. Species intolerant to drought are absent in grasslands, but present in old forest stands. Also the fraction of thelytokously reproducing microarthropods is higher in old forest stands compared with low-input grasslands. The main difference between low-input and high-input grasslands is found in the feeding guild structure of the community. Low-input grasslands are dominated by (herbo-) fungivorous grazers, whereas high-input grasslands are dominated by fungivorous browsers. Application of DDT in high-input grasslands shows a high density of microarthropods with a high fraction of thelytokous reproduction, associated with a decrease in genetic variation in a thelytokously reproducing species. Patterns in species losses, the species filters, are explained and discussed. It is shown that the decline of biodiversity is not a randorn loss of species but follows and identifiable pattern.     

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.     

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.