A metacommmunity approach to co-occurrence patterns and the core-satellite hypothesis in a community of tropical arboreal ants

Inferring mechanisms of community assembly from co-occurrence patterns is difficult in systems where assembly processes occur at multiple spatial scales and among species with heterogeneous dispersal abilities. Here, we demonstrate that local scale analysis of co-occurrence patterns is inadequate to fully describe assembly mechanisms and instead utilize a metacommunity and core-satellite approach. We generated a co-occurrence and life-history data set for a community of twig-nesting ants on coffee plants across 36 sites within a tropical agroecosystem to test the following three hypotheses: (1) twig-nesting ant species compete for nest-sites, (2) they are structured as a metacommunity, and (3) core species show segregated patterns, while satellite species show random patterns of co-occurrence. Species were divided into four groups: core species that are well distributed regionally and dominant locally, regional dominants that are well distributed regionally but do not dominate locally, local dominants that are dominant locally but are not widely distributed, and satellites that are neither widely distributed nor dominant locally. Only the most abundant species in the community, Pseudomyrmex simplex, was classified as a core species. Regional dominants, local dominants, and satellite species show random patterns of co-occurrence. However, when P. simplex is included in the co-occurrence matrix, patterns become aggregated for all three species groupings. This suggests that P. simplex “assembles” the community by providing a core metapopulation that other species track. Analyzing co-occurrence patterns among candidate subsets of species, at multiple spatial scales, and linking them to species traits substantially improves the explanatory power of co-occurrence analyses in complex metacommunities.     

Scale-dependent spatial population dynamics of gall-makers on oak

The patterns of synchrony in the population fluctuations of six species of gall‐makers on oak (Hymenoptera, Cynipidae and Diptera, Cecidomyiidae) were analyzed over a small‐scale transect (8 km) and a large‐scale transect (500 km). Gall‐maker species differed in their degree of synchrony. At the small scale some species showed synchrony among local sites, whereas at the large scale, with one exception, population fluctuations of all species were largely independent. The patterns of synchrony differed between the two spatial scales. At the small scale a considerable degree of synchrony was found among sites for two species, Cynips divisa and Neuroterus quercusbaccarum, whereas at the large scale no synchrony was seen for these species. For one species, Macrodiplosis volvens, the fluctuations were asynchronous at both the small and large scales. At the large scale, synchrony among sites was found for one species: the fluctuations of Neuroterus anthracinus were largely synchronous at both scales (i.e. over several hundred kilometers). Distance‐dependent synchronies (i.e. decreasing synchrony with increasing distance) were found for only one species, Neuroterus anthracinus. In summary, the levels of synchrony in the population fluctuations of these insects differed among species and were scale‐dependent. Scaling up from the small scale to the large scale does not seem appropriate.     

THE MYCORRHIZAE OF PIONEER SPECIES IN DISTURBED ECOSYSTEMS IN WESTERN PENNSYLVANIA

Study plots with ten types of disturbances were established in a Solidago-Aster community in western Pennsylvania. One year after disturbance, 93% of all species had vesicular-arbuscular mycorrhizae (VAM) and accounted for 92% of all plant cover. After 3 yr, 96% of the species had VAM and 96% canopy coverage. An adjacent 10-yr Solidago-Aster community had 100% VAM species. The VAM annuals, Ambrosia artemisiifolia and Setaria glauca, were major first year dominants while VAM perennials, Agropyron repens, Solidago canadensis, and Aster ericoides, dominated at 3 yr. The mean percent mycorrhizae of all dominants at 1 yr was 39% and 34% at 3 yr. Four disturbed sites had 100% VAM colonization after 1 yr and six sites after 3 yr. Severe physical disturbances (topsoil removed and topsoil-subsoil removed) resulted in complete colonization by VAM species and mean mycorrhizal infections of more than 75%. The plowed-disked-prometone and plowed-disked-vapam disturbances resulted in low levels of mycorrhizae after 3 yr. The plowed-disked-atrazine plot showed an initial severe decrease in percentage of mycorrhizae, but doubled its infection rate by 3 yr. Three non-mycorrhizal species (Chenopodium album, Rumex acetosella, and Polygonuspersicaria) were observed during the 3-yr period. C. album was the major dominant after 1 yr in the plowed-disked-fertilized site and R. acetosella a dominant in the plowed-disked-prometone plot.     

Gravel dredging alters diversity and structure of riverine fish assemblages

1. Human activities affect fish assemblages in a variety of ways. Large‐scale and long‐term disturbances such as in‐stream dredging and mining alter habitat and hydrodynamic characteristics within rivers which can, in turn, alter fish distribution. Habitat heterogeneity is decreased as the natural riffle–pool–run sequences are lost to continuous pools and, as a consequence, lotic species are displaced by lentic species, while generalist and invasive species displace native habitat specialists. Sediment and organic detritus accumulate in deep, dredged reaches and behind dams, disrupting nutrient flow and destroying critical habitat for habitat specialist species. 2. We used standard ecological metrics such as species richness and diversity, as well as stable isotope analysis of δ¹³C and δ¹⁵N, to quantify the differences in fish assemblages sampled by benthic trawls among dredged and undredged sites in the Allegheny River, Pennsylvania, U.S.A. 3. Using mixed‐effects models, we found that total catch, species richness and diversity were negatively correlated with depth (P < 0.05), while species richness, diversity and proportion of species in lithophilic (‘rock‐loving’) reproductive guilds were lower at dredged than at undredged sites (P < 0.05). 4. Principal components analysis and manova revealed that taxa such as darters in brood hider and substratum chooser reproductive guilds were predominantly associated with undredged sites along principal component axis 1 (PC1 and manova P < 0.05), while nest spawners such as catfish and open substratum spawners including suckers were more associated with dredged sites along PC2 (P < 0.05). 5. Stable isotope analysis of δ¹³C and δ¹⁵N revealed shifts from reliance on shallow water and benthic‐derived nutrients at undredged sites to reliance on phytoplankton and terrestrial detritus at deep‐water dredged sites. Relative trophic positions were also lower at dredged sites for many species; loss of benthic nutrient pathways associated with depth and dredging history is hypothesised. 6. The combination of ecological metrics and stable isotope analysis thus shows how anthropogenic habitat loss caused by gravel dredging can decrease benthic fish abundance and diversity, and that species in substratum‐specific reproductive guilds are at particular risk. The effects of dredging also manifest by altering resource use and nutrient pathways within food webs. Management and conservation decisions should therefore consider the protection of relatively shallow areas with suitable substratum for spawning for the protection of native fishes.     

Impacts of two invasive mollusks, <Emphasis Type="Italic">Rapana venosa</Emphasis> (Gastropoda) and <Emphasis Type="Italic">Corbicula fluminea</Emphasis> (Bivalvia), on the food web structure of the Río de la Plata estuary and nearshore oceanic ecosystem

This paper quantifies the impacts of two invasive species, Rapana venosa (Gastropoda, Muricidae) and Corbicula fluminea (Bivalvia, Corbiculidae), in the food web of the Río de la Plata estuary and adjacent nearshore oceanic ecosystem. We analyzed certain functional traits of these mollusks assessed by a mass balance trophic model previously constructed for the years 2005–2007. This model incorporates 37 functional groups: three marine mammals species, one coastal bird, 17 fishes, 12 invertebrates, two zooplankton, one phytoplankton, and detritus. The model also includes 5 fishing fleets operating in the area. The results showed that the two invasive species affect multiple ecosystem components both directly and indirectly. R. venosa and the whitemouth croaker, Micropogonias furnieri, exhibited a high level of niche overlap (91%), while C. fluminea exhibited a high level of niche overlap with Mytilidae (94%), which suggests in both cases high levels of competition for similar resources. R. venosa had mixed trophic impacts but exhibited a predominantly top down effect on most bivalves. R. venosa could be a threat to natural resources in the area including to the fishing fleets. C. fluminea negatively influenced phytoplankton and detritus biomass and its positive effects on higher trophic level groups suggest a central bottom-up role in the food web as a bentho-pelagic coupler. Both species had negative impacts on the five fleets modeled, showing that the effects of these invasive species could extend to the socio-economic sector.     

Detrital traits affect substitutability of a range‐expanding foundation species across latitude

Climate‐driven range shifts of foundation species could alter ecosystem processes and community composition by providing different resources than resident foundation species. Along the US Atlantic coast, the northward expanding foundation species, black mangrove Avicennia germinans, is replacing the dominant salt marsh foundation species, marsh cordgrass Spartina alterniflora. These species have distinct detrital attributes that ostensibly provide different resources to epifauna. We experimentally examined how detritus of these species affects decomposition and community composition in different habitat contexts at regional and local scales. First, we manipulated detritus identity (Avicennia, Spartina) at 13 sites across a 5° latitudinal gradient spanning mangrove, mixed marsh‐mangrove and salt marsh habitats. Across latitude, we found that Avicennia detritus decomposed 2–4 times faster than Spartina detritus, suggesting that detrital turnover will increase with mangrove expansion. Epifaunal abundance and richness increased 2–7 times from south to north (mangrove to salt marsh) and were equivalent between Avicennia and Spartina detritus except for crabs, a dominant taxonomic group that preferred Spartina detritus. Second, to examine the whether changing habitat context affected regional patterns, we manipulated detritus identity and surrounding habitat type (mangrove, salt marsh) at a single mixed site, also including inert mimics to separate structural and nutritional roles of detritus. Epifaunal richness was similar between the two detrital types, but crabs were 2–7 times more abundant in Spartina detritus due to its structural attributes. Surrounding habitat type did not influence decomposition rate or community patterns, which suggests that latitudinal influences, not surrounding habitat, drove the regional community patterns in the first experiment. Overall, mangrove expansion could alter epifaunal communities due to the lower structural value and faster turnover of mangrove detritus. As species shift with changing climate, understanding foundation species substitutability is critical to predict community change, but we must account for concomitant environmental changes that also modify communities.     

Plant species richness in the mallee region of Western Australia

Sixteen sites (area 1000 m²) within the mallee region of southern Western Australia were sampled for vascular plant species richness. Species richness ranged from 17 species per 1000m² in a Halosarcia syncarpa salt-complex site and a Eucalyptus occidentalis tree mallee site, up to 48 species per 1000 m² in a Eucalyptus angulosa-Eucalyptus tetragona shrub mallee site. Woodland, woodland/mallee and mallee sites consisted mainly of perennial species while shrubland sites and salt-complex sites had a higher percentage of ephemeral species. Sites with the highest species richness occurred on soils with the lowest nutrient content. Sites with lowest species numbers were those with severe habitat conditions or where better nutrient conditions may have provided the dominants with a competitive advantage to suppress associated species.     

Comparative dendroclimatic study of Scots pine, Norway spruce, and silver fir in the Vrancea Range, Eastern Carpathian Mountains

Using dendroclimatical methods, we compared the growth response to climate fluctuations of three of the main Romanian Carpathian Mountains coniferous species, Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karst.) and silver fir (Abies alba Mill.), growing intermixed in a unique stand. Climate and soil conditions were therefore the same for all the trees studied. The experimental site was chosen to be representative of the south-exposed sites in the Romanian Carpathian Mountains, where pine occurs naturally. In order to investigate the consequences of fluctuations in climate at different temporal scales, we examined both inter-annual and decadal time-steps. An index of soil water deficit was computed to investigate the consequences of drought. Our study reveals that species exhibited different responses to precipitation, temperature or drought. Overall, pine was the most sensitive to precipitation, while spruce showed a higher response to temperature at high frequency for both the current and the previous growing seasons, and to soil water deficit. Fir was the least sensitive species of the comparison. However, for all species, decadal modulations of growth show precipitation as a common and strong driver on the dry south-facing slopes. The results show that Scots pine would be affected more than fir by increased drought frequency and could in the future be replaced on the xeric sites.     

Colonization of ephemeral detrital patches by vagile macroinvertebrates in a brackish lake: a body size-related process?

The mechanisms regulating the build-up of invertebrate assemblages on ephemeral detritus patches are still poorly understood. Here, the daily colonization of decaying reed leaves by vagile macroinvertebrates was monitored in an brackish lake in Italy. The highly variable abundance patterns of dominant taxa were analysed by spectral and geostatistical techniques to test for nonrandomness and to further determine whether they were related to body size. Comparisons between two contrasting sites allowed an assessment of the generality of our observations. At both sites, the macroinvertebrate assemblage was dominated by three detritivorous taxa, i.e. the isopod Lekanesphaera monodi, the amphipod Microdeutopus gryllotalpa and the polychaete Neanthes caudata. Overall, their abundance patterns were characterised by short-term fluctuations of a nonrandom, autocorrelated nature. In addition, a significant covariation was observed between the average body mass of each taxon and the complexity of the respective abundance pattern, expressed by the fractal dimension D. The covariation was observed at both study sites, notwithstanding the diverging outcomes of bivariate pattern comparisons for similar-sized taxa. Our findings indicate that the size of macroinvertebrates is strongly related to the short-term dynamics of their abundance patterns on reed detritus, suggesting that the interaction between vagile consumers and ephemeral resource patches might be influenced by individual energetics. The implications of size-related constraints for the coexistence of species on decaying detrital patches are discussed.     

Distribution and habitat utilization in two atyid shrimps (Crustacea: Decapoda) in rivers of Nuku-Hiva Island (French Polynesia)

The distribution of Atyoida pilipes (Newport, 1847) and Caridina weberi De Man, 1892 was studied at two spatial scales on Nuku-Hiva Island (Marquesas, French Polynesia). At the stream reach scale, the two species were present at 40 and 39 sites, respectively, out of a total of 49 sites sampled. These two taxa represented more than half of the invertebrates collected at 9 sites. There was no difference in distribution between the species at the reach scale. However, clear differences appeared between the two species at the microhabitat scale. A. pilipes was more abundant in lotic habitats, even waterfalls, while C. weberi was associated with accumulations of leaves in lentic habitats. A. pilipes, particularly males, were tolerant to parameters such as water velocity, leaves, and the presence of algae and rocks. C. weberi had a more restricted altitudinal distribution and were scarce upstream from large waterfalls. These differences were linked to differences in climbing ability rather than the effect of chemical parameters, such as oxygen content. Our results suggest that little competition for space or food resources occurs between the two species. Both are feeding on small detritus particles, but through differing mechanisms and in differing habitats.     

Fish bioenergetics model used for estimation of food consumption in a navigation canal with heavy traffic

Fish were sampled in two successive years in a canal in north-west England with heavy boat traffic (10000 mh^–1yr^–1). An energy budget was used to calculate the food consumption of the two most dominant species, roach Rutilus rutilus and gudgeon Gobio gobio. For two subdominant (perch, Perca fluviatilisand ruffe, Gymnocephalus cernuus) and four rare species living there, parameters of the energy budget and prey consumption were estimated using ecological indices calculated for both dominants. The food conversion efficiency was low compared with values for the same species in other habitats, probably because of detritus and scarcity of macrobenthos in the diet. This may have been a result of the heavy boat traffic.     

Early herbaceous succession along a topographical gradient on forest clear-felling sites in mountainous terrain,central Japan

Early successional patterns of herbaceous communities in forest clear-felling sites were investigated along a topographical gradient, which included ridge, slope and valley habitat types, in warm-temperate evergreen forest regions of central Japan for 5 years. Three dominant species with wind-dispersed seeds played a major role in the succession: an annual,Crassocephalum crepidioides, a biennial,Erigeron canadensis, and a perennial,Miscanthus sinensis. Pioneer herbs that have a seed-bank strategy, which are common in old field succession, were not found in the mountainous sites. The persistence of the annual or biennial dominants during the very early stages of secondary succession was different in the three topographical habitat types. In the ridge habitat,M. sinensis dominated from the first year state, andC. crepidioides andE. canadensis were less prominent.Crassocephalum crepidioides andE. canadensis became dominant as one moved down the slope. In the valley habitat,C. crepidioides dominated in the first year stage, was succeeded byE. canadensis in the second year, and thenM. sinensis gradually replaced it in later years. As all three wind-dispersed dominants simultaneously invaded in all the habitat types after clear-felling, the different successional patterns along the topographical gradient might have resulted from differences in the establishment ability and the growth rate of the three dominants depending on the three habitat types.     

Ant community structure on a small Pacific island: only one native species living with the invaders

In most studies about ant communities, species are grouped into competitive hierarchies where top dominants drive the majority of other species away from resources. Nevertheless, in some ecosystems high ground temperatures may disrupt this hierarchical organization. Other changes in community structure are caused by the arrival of invasive ant species, which rapidly disassemble local communities. We studied the effects of competition and temperature on ant community organization on Surprise Island (New Caledonia). Four different habitats were distinguished: a central plain, a sea shore Argusia shrubland, a dense Scaveola shrub, and an arboreal Pisonia strata. Eight ant species were identified from pitfall traps (seven introduced and only one native species, Pheidole oceanica). Ant assemblages in each habitat had a different ecologically dominant species, and a dominant species in one habitat could be non-dominant and less abundant in another. From interactions at baits, we built a competitive hierarchy where the top dominant species was the native Ph. oceanica. Daily foraging activity rhythms of the different species mostly overlapped. The relationship between bait occupation and ground temperature followed a negative linear pattern at all sites and for most species, except for the relatively thermophilous Monomorium floricola. Indices of co-occurrence in pitfall traps indicated that species co-occurred randomly with respect to one another. Conversely, species appeared to be segregated when we examined co-occurrence at baits at the sites where Ph. oceanica was abundant. Oceanic islands are very susceptible to alien species, but on Surprise Island it seems that the sole native species dominates in some habitats when confronted by invasive species.     

Feeding habits and food resources of filter-feeding Trichoptera in a regulated mountain stream

A year-round study was conducted to examine feeding habits and food resources of the filter-feeding Trichoptera Arctopsyche grandis and Brachycentrus occidentalis along a regulated mountain stream gradient. There was a well defined longitudinal species replacement with A. grandis reaching maximum densities 2.3 kilometers below the impoundment, and concomitant with its decline downstream was an increase in B. occidentalis. At all sampling sites the < 75 µm organic seston fraction usually consisted primarily of diatoms (>70%, by areal estimate on microscope slides), whereas the 75–250 µm and > 250 µm seston fractions were predominantly composed of detritus (> 80 %). B. occidentalis larvae consumed primarily detritus and diatoms (> 70 % of the diet), while A. grandis ingested a variety of materials with animals, detritus and/or filamentous algae often constituting > 80% of the diet. Animal material was over-represented in the diets of both species when compared with amounts in the seston. Feeding habits provided partial explanations for the distinct longitudinal distribution patterns of filter-feeding Trichoptera observed in the regulated river.     

Long-term vegetation dynamics in the Šumava Mts. natural spruce-fir-beech forests

In 1972(74)–1996(98), repeated phytocoenological surveys of natural mixed forest remainders were made on permanent plots in the Šumava Mts. in the south-western part of the Czech Republic. The surveys were made in localities with subsoils poor in nutrients (Boubín-Milešice—27 plots) and in a locality with nutrient-rich subsoil (Stožec—15 plots). Vegetation dynamics were studied according to the year of measurement and the nutrient capacity of the geological bedrock. We used the indices of floristic similarity, the calculation of plant communities’ characteristics (Shannon–Wiener’s index, equitability index), the calculation of taxa characteristics (fidelity, average cover, constancy) and multivariate ordination analyses—indirect (DCA) and direct (CCA). Changes in environmental conditions were studied between the years of measurement and between the localities using bioindication—by the calculation of Ellenberg indicator values (EIV) for plant communities. Over 24 years both the nutrient-poor site and the nutrient-rich site showed a considerable reduction in the tree layer cover and conversely the advancement of shrub layers. The coverage degree of dominants in the main tree layer (Fagus sylvatica, Picea abies and Abies alba) markedly decreased. Abies alba also exhibited a pronounced drop in constancy. On the other hand, the lower tree layer and shrub layers in Boubín-Milešice exhibited a distinctive invasion of Fagus sylvatica. An increase in the frequency of Sorbus aucuparia and a decrease in the frequency of Ulmus glabra were determined too. Herb layer changes were highly significant between the 1970s and the 1990s with qualitative changes being greater than quantitative changes. The number of species and Shannon–Wiener’s index increased. A significant difference was recorded between the nutrient-poor and the nutrient-rich sites in the values of the quantitative similarity of relevés with other differences being insignificant. The nutrient-poor sites exhibited herb layer homogenisation. A significant increase of EIV for light was found on both site types. The changes in phytocoenoses were interpreted partly as developmental trends (caused by indirect impact of man—e.g. fluctuations in game populations since the 18th century, the impact of air pollution); partly as cyclical changes connected with the developmental cycle of the natural temperate forest.     

Oviposition habitat selection by container‐dwelling mosquitoes: responses to cues of larval and detritus abundances in the field

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Escapes from herbivory in relation to the structure of mangrove island macroalgal communities

Summary Some shallow habitats that surround mangrove islands exhibit abruptly discontinuous macrophyte boundaries; in other regions, plant distributional patterns are less defined. Where distinct boundaries do occur, fleshy algae predominate on the roots of the red mangrove, Rhizophora mangle, which do not contact the bottom sediments (hanging roots), while calcifying algae dominate on the substratum-penetrating roots and banks (=embedded-root habitat) surrounding the mangrove thickets. Considerable natural-history and floristic information reveals that the fleshy hanging-root species are not specialists, for that type of habitat. Experimental transplants showed that on banks and embedded roots where there typically are abundant macroherbivores (particularly sea urchins), most fleshy algae are eliminated.The dominants of the hanging-root habitat (e.g, Acanthophora spicifera, Spyridia filamentosa, Caulerpa racemosa var. Occidentalis) are 6–20 times more susceptible to herbivores than the dominants of the embedded-root habitat (e.g., Halimeda opuntia f. triloba, H. monile). Consequently, we suggest the former are relegated to the spatial refugia from herbivores (=non-coexistence escapes) provided by the hanging roots. Factors associated with these palatability differences include higher average calorific values (6.5 times) of the fleshy hanging-root dominants, greater proportions of organic content (2.6 times) and the general absence of calcification. The dominants of the embedded-root habitat show reduced edibility as a probable consequence of low calorific values, heavy calcification and potential herbivore-detering secondary metabolites. Correlative evidence and preliminary experimental results tentatively indicate that, in the absence of macroherbivores, the hanging-root dominants, which exhibit production rates 4.7 times greater than the dominants of the embedded-root habitat, are better competitors for space.We suggest that variations in herbivory are responsible, in part, for maintaining greater algal diversity in mangrove systems. At a study site with abundant sea urchins, five algal species were found only in the embedded-root habitat three species were confined to the hanging roots, while three others occurred in both. At an urchin-free site, no macrophytes were found only on embedded-root substrata, while one (in trace amounts) was found only on hanging-root habitat and eight occurred in both. We predict that in the absence of herbivores, the species assemblage characteristic of the hanging-roots would exclude many of the dominants from the embedded-root habitat.     

Growth limitation of three Arctic sea ice algal species: effects of salinity, pH, and inorganic carbon availability

The effect of salinity, pH, and dissolved inorganic carbon (TCO₂) on growth and survival of three Arctic sea ice algal species, two diatoms (Fragilariopsis nana and Fragilariopsis sp.), and one species of chlorophyte (Chlamydomonas sp.) was assessed in controlled laboratory experiments. Our results suggest that the chlorophyte and the two diatoms have different tolerance to fluctuations in salinity and pH. The two species of diatoms exhibited maximum growth rates at a salinity of 33, and growth rates at a salinity of 100 were reduced by 50% compared to at a salinity of 33. Growth ceased at a salinity of 150. The chlorophyte species was more sensitive to high salinities than the two diatom species. Growth rate of the chlorophyte was greatly reduced already at a salinity of 50 and it could not grow at salinities above 100. At salinity 33 and constant TCO₂ concentration, all species exhibited maximal growth rate at pH 8.0 and/or 8.5. The two diatom species stopped growing at pH > 9.5, while the chlorophyte species still was able to grow at a rate which was 1/3 of its maximum growth rate at pH 10. Thus, Chlamydomonas sp. was able to grow at high pH levels in the succession experiment and therefore outcompeted the two diatom species. Complementary experiments indicated that growth was mainly limited by pH, while inorganic carbon limitation only played an important role at very high pH levels and low TCO₂ concentrations.     

Plant genotype identity and diversity interact with mesograzer species diversity to influence detrital consumption in eelgrass meadows

Seagrass meadows are among the world's most productive ecosystems, and as in many other systems, genetic diversity is correlated with increased production. However, only a small fraction of seagrass production is directly consumed, and instead much of the secondary production is fueled by the detrital food web. Here, we study the roles of plant genetic diversity and grazer species diversity on detrital consumption in California eelgrass Zostera marina meadows. We used three common mesograzers—an amphipod, Ampithoe lacertosa, an isopod, Idotea resecata, and a polychaete, Platynereis bicanaliculata. Each grazer consumed eelgrass detritus at rates greater than live eelgrass or macroalgae. This detrital consumption, however, was not spread evenly over leaves shed from different eelgrass clones. Palatability and consumption varied because of genotype specific differences in leaf texture, secondary metabolites (phenolics), and nutritional quality (nitrogen). Further, detritus derived from some eelgrass genotypes was palatable to all grazers, while detritus from other genotypes was preferentially consumed by only one grazer species. Under monospecific grazer assemblages, plant genetic identity but not diversity influenced detritus consumption. However, more realistic, diverse mesoconsumer communities combined with high plant‐detrital genotypic diversity resulted in greater consumption and grazer survival. These results provide a mechanism for field observations of increased mesograzer density and diversity in genetically diverse seagrass assemblages and offer a potential explanation for variation in results of resource diversity– detrital processing experiments in the literature, which often exclude macroinvertebrate taxa. More broadly, our findings support the emerging principle that biodiversity effects are strongest when diversity in both consumer and resource taxa are present.     

Life history and larval feeding of some species of Ephemeroptera and Plecoptera (Insecta) in the Sierra Nevada (Southern Iberian Peninsula)

We monitored two high mountain streams from the Sierra Nevada (Southern Spain) monthly throughout an annual cycle, measuring and analyzing physical and chemical parameters. Temperature was hourly registered. We studied life cycles and larval feeding of four mayfly species [Serratella ignita (Poda, 1761), Serratella spinosa nevadensis (Alba-Tercedor, 1981), Alainites muticus (Linnaeus, 1758), and Baetis alpinus Pictet, 1843] and two stonefly species [Amphinemura triangularis (Ris, 1902) and Capnioneura mitis Despax, 1932]. Some species changed their strategies (growth rate, life cycle duration, and/or voltinism) in accordance with different conditions (depending on the altitude and temperature). The gut content data showed that species fed mainly on detritus (as collector-gatherers or as shredders), except B. alpinus that behaved as a scraper in one of the streams. Differences in the larval diet of the same species in different streams, and even through its life, support the idea of not using general models to extrapolate the function of a species from a higher taxonomical level. Handling editor: D. Dudgeon