Measuring community responses to large-scale disturbance in conservation biogeography

Aim   Which community metrics should be used to reflect community response to large-scale habitat alterations is unclear. Here, we assess what and how community changes should be measured to accurately track community responses to large-scale disturbance in space and/or time.
Location   France.
Method   We first developed a simulation model to examine temporal changes in the species composition of large-scale metacommunities. Using this model, we assessed how species richness, Shannon index, trends of particular subset of species or community indices of habitat specialization were influenced by different disturbance scenarios, and whether these indices were biased by imperfect detectability. We further used more than 1000 empirical bird communities from the French Breeding Bird Survey recently exposed to disturbances of various intensities as a case study.
Results   Our simulation and empirical results both demonstrate that species richness and diversity measures can show confusing trends and even provide misleading messages of communities' fate. In contrast, reflecting the composition of the community in terms of habitat specialist and generalist species was more robust and powerful to reflect disturbance effects.
Main conclusions   We highlight the weakness of using community metrics that fail to incorporate ecological difference among species when summarizing community-level trends in disturbed landscapes.     

Experimental evidence of the dynamic effect of free-floating plants on phytoplankton ecology

1. There is an increasing concern to understand the role of free-floating plants (FFP) on the functioning and structure of shallow lakes, particularly the mechanisms by which their dominance is self-stabilizing and how they may outcompete phytoplankton.
2. In a field experiment with mesocosms, we simulated three commonly encountered scenarios in warm temperate shallow lakes: FFP dominance, FFP fluctuation and FFP absence. We explored the effects of several key processes, triggered by FFP dynamics, on the composition, diversity and production of phytoplankton, and on the physicochemical conditions.
3. The effects of persistent floating mats on light interception triggered a complex response by the phytoplankton: species were lost and biomass was low, yet high diversity and productivity potential were maintained. A contrasting phytoplankton response characterized mesocosms lacking FFP, where light was sufficient but nitrogen was limiting. Fluctuating FFP cover brought periodic shifts between these two limiting resources for the phytoplankton, which most probably explain the maintenance of richness, diversity and production in these shallow lakes.
4. These results support the recently proposed framework of alternative stable states, providing experimental field evidence of the mechanisms resulting from the shifts between floating plants and phytoplankton dominance.     

Butterfly response to severe ENSO-induced forest fires in Borneo

Abstract.  1. Little is known about animal community response to severe El Niño Southern Oscillation (ENSO)-induced fire events. Here the response of butterflies to the 1997/98 ENSO-induced fire event in East Kalimantan (Indonesian Borneo) is assessed. In addition to the community-wide study, a detailed assessment of the lycaenid Jamides celeno is made.
2. Species richness declined significantly from 211 species pre-ENSO to 39 species post-ENSO and community composition changed significantly. Along with the decline in species richness there was a marked increase in dominance. Jamides celeno , for example, increased from 3% of the pre-ENSO assemblage to 58% of the post-ENSO assemblage. Like J. celeno , most of the species in the post-ENSO assemblage were generalists; most of the specialist species having disappeared from pre- to post-ENSO.
3. The major host plant used by J. celeno was the abundant resprouting Fordia splendidissima . Furthermore, significantly more eggs were laid on plants with the crazy ant, Anoplolepis gracilipes , present than on plants with other ants or no ant attendance. Caterpillar presence was significantly higher on plants tended by ants than on untended plants.
4. The median distance moved by J. celeno was 30 m with a maximum recorded distance of 290 m.
5. The abundance of J. celeno and other generalists in the post-ENSO assemblage at Wanariset was probably related to their ability to utilise the few available resources after the fire (e.g. F. splendidissima resprouts), their presence in degraded habitats surrounding the Wanariset forest, and their ability to disperse successfully by either being strong fliers (e.g. Euploea spp.) or being able to attain very high population sizes and thereby produce a surplus of dispersers (e.g. J. celeno ).     

Are distribution patterns linked to dispersal mechanism? An investigation using pond invertebrate assemblages

1. Dispersal ability influences the distribution and abundance of organisms, but empirical investigations of the relationship between dispersal ability and the composition of ecological assemblages are scarce. Here, we compare between-site variation in the species richness and community composition of actively and passively dispersing pond invertebrates.
2. Coleoptera (active dispersers) and microcrustacea (passive dispersers) were sampled over a season from 16 ponds within a 4-km radius in south-west England. Species richness and community composition were related to environmental variables using regression and Canonical Correspondence Analysis (CCA), respectively.
3. Coleopteran species richness was significantly and positively correlated with pond permanence and maximum area, whereas microcrustacean species richness was relatively equal across sites and did not correlate with environmental variables. The frequency of species' occurrence between sites was the same for both groups, which suggests that active and passive dispersers exhibited the same degree of dispersal.
4. Between-site variation in community composition was non-random for both groups, with pond permanence and area, together, explaining similar proportions of between-site variation for Coleoptera. Permanence was correlated most strongly with microcrustacean community composition and a high proportion (25%) of microcrustacean species were more numerous in smaller, more ephemeral ponds.
5. These data suggest that, at small spatial scales, Coleoptera which can undertake multiple dispersal events, are more likely to colonise large, more permanent ponds than passively dispersing microcrustacea. For microcrustacea, other traits (in this case those permitting existence in ephemeral habitats) may over-ride the influences of dispersal in driving between-site variation in species composition.     

Responses of phytoplankton and epilithon during acidification and early recovery of a lake

1. Lake 302S in the Experimental Lakes Area of Canada was acidified from pH 6.7 (1981) to 5.1 (1986). The pH was further reduced to 4.5 in 1987 and held at that level until 1991. From 1992 to 1995, the pH was allowed to increase to a target value of 5.8.
2. The response of the phytoplankton community to decreasing pH from 6.0 to 5.1 was similar to that observed in another experimentally acidified lake (223) and in other atmospherically acidified lakes. Acidification affected species diversity of both the phytoplankton and epilithon. Phytoplankton diversity was positively correlated with pH. Epilithic algal diversity was more variable and did not correlate with pH.
3. Phytoplankton biomass was enhanced by acidification as the assemblage shifted from a dominance of chrysophytes to large dinoflagellates ( Gymnodinium sp. and Peridinium inconspicuum ). Epilithon biomass was unaffected, but dominance shifted from filamentous cyanophytes ( Lyngbya ) to acidophilic diatoms ( Tabellaria quadriseptata and Anomoeonis brachysira ).
4. The only taxon to be similarly affected in both the phytoplankton and epilithon was the cyanobacteria, being significantly reduced below pH 5.1. During early recovery (pH 5.5–5.8), cyanobacteria increased and species present prior to acidification recolonized both habitats.
5. In the early stages of recovery, planktonic and benthic assemblages remained more similar to acidified than natural assemblages, but more profound change began at pH > 5.5.     

Do battles lead to coexistence? Role of interference competition in structuring the insect community on fermented tree sap

Abstract.  1. In insect communities on fermented tree sap, agonistic interactions occur frequently among the component species. This study examined the effects of such interference competition on community structure and species co-occurrence on a spatio-temporally small scale.
2. Experimental removal of giant hornets ( Vespa mandarinia ), one of the most dominant species, showed no effect on either species richness or total abundance of the remaining insects. Significant increases in abundance were detected for five out of 19 taxa: V. ducalis , V. crabro , Lasius japonicus , Cryptarcha lewisi , and a group of micro sap beetles ( Epuraea spp., Haptoncus spp., and Haptoncurina spp.).
3. Behavioural observations indicated that interference did not alter the staying time at a patch (an exuding spot on a tree) for V. mandarinia , Rhomborrhina japonica , and Neope goschkevitschii . Interference-mediated departure from a patch was less frequent than departure without interference for all nine species observed, except for R. japonica . These behavioural contexts varied yearly for several species.
4. These results suggest that interference competition is a minor determinant of overall community structure, despite its conspicuousness. This weak effect of interference may be attributed to the short stay of dominant species and to individual behavioural responses, such as competitor avoidance. The variable influence of interference might be related to differences in species attributes, such as dominance hierarchies.     

Colonising aliens: caterpillars (Lepidoptera) feeding on Piper aduncum and P. umbellatum in rainforests of Papua New Guinea

Abstract.  1. Caterpillar assemblages feeding on two alien plants, Piper aduncum and P. umbellatum , were studied in lowland rainforest in Papua New Guinea and compared with assemblages from 69 species of native woody hosts, including congeneric P. macropiper .
2. Species richness of caterpillars feeding on P. aduncum (29 species per 1500 m² of foliage) and P. umbellatum (36 species) was higher than the median richness for the 69 native hosts (23 species).
3. The probability that a caterpillar species colonised alien Piper increased with its host range from 3% for the species feeding on a single plant family to 92% for the species with host range >10 plant families.
4. The assemblage on P. aduncum was dominated by a single species ( Herpetogramma sp. near licarsisalis , Crambidae), which represented 48% of individuals, and also had a high proportion (34%) of rare species, collected as single individuals. This community structure was indistinguishable from that of a typical native host. In contrast, the P. umbellatum assemblage was unusual as no species represented >10% of individuals.
5. The aggressive invasion by P. aduncum of early successional vegetation is not explained by a competitive advantage due to low herbivore load, as the abundance of caterpillars feeding on it was comparable to that of native pioneer plants.
6. The caterpillar assemblage on P. aduncum demonstrated that an assemblage indistinguishable from native assemblages in density, species richness, and dominance structure (but not in host specificity) can originate from the existing species pool in lowland rainforests on a recently established tree species in <50 years.     

Predicting the spatial dominance of phytoplankton in a light limited and incompletely mixed eutrophic water column using the PROTECH model

1. A phytoplankton community model [Phytoplankton RespOnses To Environmental CHange (PROTECH)] was used to examine the effect of a wide range of varied light intensities and mixed depths upon simulated phytoplankton populations. Two different column lengths of the simulated water body were examined (the upper 5 m and the whole 14.5 m water column) for each scenario.
2. The hypotheses tested were that: (i) under low light intensity and/or deep mixing the simulated community will be dominated by a phytoplankter with a low critical light intensity; (ii) at high light intensity and shallow mixing the simulated community will be dominated by small, fast-growing phytoplankters; (iii) under all conditions, except deep mixing, the largest proportion of phytoplankton biomass will be found near the surface.
3. It was found under most conditions that, although there was a bloom in the upper column (dominated by algae such as Chlorella , Ceratium or Rhodomonas ), the largest phytoplankton biomass in the water column was located 9 m below the surface and consisted of solely Asterionella . This bloom was missed by the 5-m samples. Thus, using the whole column sample lengths, hypothesis (i) was not rejected but hypotheses (ii) and (iii) were refuted.
4. The inclusion of specific movement characteristics of phytoplankton in the model allowed the possibility of the dominance of multiple spaces within the water column and should be included in any model-based investigation of this topic. Further, the results from the model suggest that a reduced depth of mixing creates greater environmental heterogeneity, allowing more species to persist.     

Community structure of arboreal caterpillars within and among four tree species of the eastern deciduous forest

Abstract.  1. A seasonally replicated experimental design was used to address the question of how differences within and among host tree species affect arboreal caterpillar communities.
2. Seasonal variation influenced caterpillar community composition most significantly, and the similarity among caterpillar assemblages did not necessarily follow the pattern of phylogenetic relatedness among host trees.
3. Species richness and abundance of caterpillars were higher on oaks and maples than on American beech. Diversity partitioning models revealed that β diversity was only occasionally greater or less than expected by chance alone.
4. When β diversity was significant, values tended to be greater than expected by chance among replicate trees within each species and lower than expected by chance among the four tree species.
5. Differences among trees appeared important for determining patterns of species presence/absence for rare species and influencing patterns of species dominance within caterpillar assemblages. Differences among tree species had a significant effect on overall lepidopteran community composition and mean species diversity (i.e. α diversity).
6. Because β diversity of caterpillars among host trees was lower than expected by chance, host specificity within the Lepidoptera may be less prevalent than thought previously.     

Microclimate and tree community linked to differences in lepidopteran larval communities between forest fragments and continuous forest

Aim  We aim to assess the impact of forest fragmentation on lepidopteran larval community and study the associations of microclimate and tree community with lepidopteran assemblage.
Location  Kibale National Park, Uganda.
Methods  We investigated the effects of forest fragmentation on leaf herbivory, density of lepidopteran caterpillars, species richness and diversity as well as the composition of herbivorous lepidopteran larval community. Microclimate, size of the fragment, distance to the continuous forest, and tree diversity were studied as possible explanatory factors. We sampled 10 Neoboutonia macrocalyx Pax. (Euphorbiaceae) trees in each fragment during dry and rainy season, total of four times, in a year to cover the seasonal variation.
Results  The rates of herbivory, total larval density and species richness were significantly lower in the forest fragments than in the continuous forest but species diversity expressed as Fisher's alpha did not differ. The dominance structure and community composition of the larval communities in the fragments was different from that of the continuous forest. None of the differences we observed were related to the fragment area or distance to the continuous forest. Instead, we found an indication of association between the herbivore and the tree communities. The fragments had significantly lower humidity during most of the day and higher temperature during the afternoons (14–17 h), which might partially explain the differences in lepidopteran larval communities.
Main conclusions  Decreased larval density and species richness as well as differences in the community composition and structure all highlight the importance of large continuous forest areas for maintaining larval biodiversity.     

Elevation gradients of diversity for rodents and bats in Oaxaca, Mexico

1  This study documents patterns of rodent and bat diversity related to abiotic and biotic factors along elevational gradients in the Sierra Mazateca (640–2600 m a.s.l.) and Sierra Mixteca (700–3000 m a.s.l.) in Oaxaca, Mexico.
2  The two transects share similar faunas: 17 and 23 rodent species were captured in the sierras Mazateca and Mixteca, respectively, 14 of which occurred on both transects. Rodent species richness was similar in the wet season and the dry season along both transects. Rodent species richness peaked at 1025–1050 m in tropical semi-deciduous forest on both transects. Endemic species were restricted to high-elevation habitats.
3  Sixteen and 17 bat species were captured in the sierras Mazateca and Mixteca, respectively; 11 occurred on both transects. Bat species richness was higher in the wet season than in the dry season in the Sierra Mazateca. Bat species richness peaked at 1850 m in pine–oak forest in the Sierra Mazateca, and at 750 m and 1050 m in tropical semi-deciduous forest in the Sierra Mixteca, decreasing abruptly at higher elevations on both transects.
4  Patterns of trophic diversity of rodents and bats coincided with those of species richness on each transect. Species richness increased with increasing habitat diversity; increased with increasing rainfall and productivity; increased with increasing resource diversity; and increased in areas with high rates of speciation (rodents only).
5  The need for conservation action in Oaxaca is urgent and proponents should promote establishment of protected areas linking lowland habitats with high species richness to high-elevation habitats harbouring large numbers of endemic forms.     

Seasonal variation in the abundance, biomass and biodiversity of earthworms in soils contaminated with metal emissions from a primary smelting works

1. Earthworms (Annelida: Oligochaeta) were sampled on four occasions (spring, summer, autumn and winter) at 14 sites along two transects from a primary lead/ zinc/cadmium smelting works at Avonmouth, UK.
2. Total abundance and biomass of earthworms decreased with proximity to the smelter. No worms were collected from the two sites closest to the factory (<0·6 km) and catches were significantly lower than controls at a further five sites (<3 km).
3. Seasonal composition of sampled communities differed only for summer with lower numbers of individuals and species collected at all sites. Reduced catches in the summer sample is a response to drought.
4. Species richness was lowest at sites close to the factory. For example, worms such as Aporrectodea caliginosa (Savigny) and Allolobophora chlorotica (Savigny) that were dominant at relatively clean sites further from the smelter are absent from the most contaminated soils.
5. Reduced species richness resulted in lower Shannon–Weiner diversity and higher Berger–Parker dominance. Multivariate cluster analysis for spring, summer and winter indicated that sites could be split into three groups based upon relative species composition. In autumn, two clusters were identified.
6. The absence of sensitive species from sites close to the smelting works supports the inclusion of earthworms as a key group in a terrestrial prediction and classification scheme for quantifying the effects of pollutants on soil biodiversity. However, sampling should be carried out in spring or autumn to obtain an accurate picture of community structure.     

Testing a biological mechanism of the insurance hypothesis in experimental aquatic communities

1.  The insurance hypothesis predicts a stabilizing effect of increasing species richness on community and ecosystem properties. Difference among species' responses to environmental fluctuations provides a general mechanism for the hypothesis. Previous experimental investigations of the insurance hypothesis have not examined this mechanism directly.
2.  First, responses to temperature of four protist species were measured in laboratory microcosms. For each species, we measured the response of intrinsic rate of increase ( r ) and carrying capacity ( K ) to temperature.
3.  Next, communities containing pairs of species were exposed to temperature fluctuations. Community biomass varied less when correlation in K between species (but not r ) was more negative, and this resulted from more negative covariances in population sizes, as predicted. Results were contingent on species identity, with findings differing between analyses including or not including communities containing one particular species.
4.  These findings provide the clearest support to date for this mechanism of the insurance hypothesis. Biodiversity, in terms of differences in species' responses to environmental fluctuations (i.e. functional response diversity) stabilizes community dynamics.     

The importance of sward architectural complexity in structuring predatory and phytophagous invertebrate assemblages

Abstract.  1. Although the importance of plant community assemblages in structuring invertebrate assemblages is well known, the role that architectural complexity plays is less well understood. In particular, direct empirical data for a range of invertebrate taxa showing how functional groups respond to plant architecture is largely absent from the literature.
2. The significance of sward architectural complexity in determining the species richness of predatory and phytophagous functional groups of spiders, beetles, and true bugs, sampled from 135 field margin plots over 2 years was tested. The present study compares the relative importance of sward architectural complexity to that of plant community assemblage.
3. Sward architectural complexity was found to be a determinant of species richness for all phytophagous and predatory functional groups. When individual species responses were investigated, 62.5% of the spider and beetle species, and 50.0% of the true bugs responded to sward architectural complexity.
4. Interactions between sward architectural complexity and plant community assemblage indicate that the number of invertebrate species supported by the plant community alone could be increased by modification of sward architecture. Management practices could therefore play a key role in diversifying the architectural structure of existing floral assemblages for the benefit of invertebrate assemblages.
5. The contrasting effects of sward architecture on invertebrate functional groups characterised by either direct (phytophagous species) or indirect (predatory species) dependence on plant communities is discussed. It is suggested that for phytophagous taxa, plant community assemblage alone is likely to be insufficient to ensure successful species colonisation or persistence without appropriate development of sward architecture.     

The community-wide and guild-specific effects of pubescence on the folivorous insects of manzanitas Arctostaphylos spp.

Abstract.  1. Insect communities on 26 species of manzanita Arctostaphylos spp. (Ericaceae) were sampled in order to examine the effects of variation in foliar pubescence traits on a community of folivorous insects. Manzanitas vary widely in pubescence density, length, and glandularity both within and between species.
2. Linear models were fitted and evaluated to determine whether pubescence traits are associated with the species richness and abundance of folivorous insects after accounting for the effects of other relevant habitat and host-plant related characteristics.
3. Pubescence traits were clearly associated with both community-wide and guild-specific variation in the structure of the folivorous insect community of manzanitas, however the effects of pubescence were manifested primarily as effects on the abundance of folivores not on species richness. The species richness of folivorous insects on manzanitas was not associated with pubescence density or length but was associated positively with glandularity.
4. The abundance of all guilds except leaf-mining insects was lower on manzanitas having longer pubescence. In contrast, the abundance of external-chewing insects was higher on plants having denser pubescence and on plants having glandular pubescence.
5. Overall, the results suggest that both longer pubescence and the amount of contact between an insect and pubescence act quantitatively to decrease the abundance of external-feeding guilds of folivorous insects. The abundance of species in internal-feeding guilds that oviposit directly on leaves is unrelated to foliar pubescence traits in the host plant.     

Changes in the plankton community following introduction of filter-feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter-feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined.
2. During a summer experiment, a bloom of Anabaena flos-aquae developed (≈ 8000 cells mL⁻¹) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700–14 400 organisms L⁻¹) after the bloom in this fish-free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass.
3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (≈ 24 °C) inhibited active feeding of this warm-water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans.
4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.     

Comparison of lepidopteran larval communities among tree species in a temperate deciduous forest, Japan

Abstract.  1. The enormous diversity of phytophagous insects in forest canopies is hypothesised to be supported by the number of herbivorous species per host tree species or host specificity. It is therefore necessary to examine the effect of host plant species on compositional changes in the herbivore communities.
2. The lepidopteran larval communities were examined in the canopies of 10 tree species in a temperate deciduous forest of Japan. The phylogeny and leaf flush phenology of host plant species were taken into account as factors affecting the herbivore community assembly.
3. Examination of seasonal changes in the larval community structures on each tree species showed that larval species richness, abundance, and evenness decreased significantly from spring to summer. Larval species richness and abundance were characterised by family-level phylogenetic differences among tree species, whereas evenness was determined at a higher taxonomic level.
4. Compositional changes in the larval communities among tree species showed a remarkable pattern, with a phylogenetic effect at a high taxonomic level in spring, similar to evenness, but a phenological effect in summer. This suggests that host specificity could support the lepidopteran larval diversity in spring.
5. These results suggest that the differences in host utilisation of the herbivore, which reflects the phylogenetic effect of the host plants, can be important as a factor affecting the diversity of lepidopteran larval communities in temperate forests.     

Zooplankton biomass and community structure in a Danube River floodplain system: effects of hydrology

1. Zooplankton density and biomass was examined in a Danube River floodplain section with highly variable hydrological dynamics. Temporal patterns were analysed to assess the effects of hydrological conditions on zooplankton community structure and the differential response of the two major zooplankton taxa, rotifers and crustaceans.
2. Calculated floodplain water age was used as an integrated parameter describing hydrological conditions and connectivity.
3. Total zooplankton biomass, crustacean biomass and crustacean species number were significantly positively related to water age. Rotifer biomass followed a hump-shaped relationship with water age, and rotifer species number decreased with increasing water age.
4. Rotifers dominated the community in periods of low to medium water ages. In periods of higher water ages the community was dominated by crustaceans.
5. We propose that the hydrological regime of floodplains is crucial for zooplankton biomass patterns and succession, through the alternation of washing-out effects, taxon-specific potential of reproduction and biological interactions. Flood events and high water levels reset the community to an early successional phase.     

Water quality and phytoplankton community structure in mangrove streams under different logging regimes in Cameroon

Mangrove logging is rampant, and its effects on phytoplankton dynamics have not been investigated. Phytoplankton are valuable in biomonitoring pollution in mangrove ecosystems. This study assessed the relationship between physico‐chemical characteristics of the water and observed phytoplankton community structure, in relation to anthropogenic activities. Water samples were collected from seven sites within the mangrove ecosystem that differed in wood harvesting age and proximity to human settlements. Characterization of samples followed standard methods. pH of all water samples indicated acidity. Phytoplankton species richness and soluble P were positively correlated (r = 0.822, P ≤ 0.023), but no correlations existed with logging age (r = ?0.273, P = 0553). The site with highest soluble phosphorus concentration (Site 4) had highest phytoplankton abundance, diversity and richness. A total of 127 species were identified in 58 families. Euglenaceae was the most abundant family (13 species) and Anacystis sp. the most frequent species (100%). The most common genera were Microcystis and Anacystis, bioindicators of pollution. The site at which harvesting was most recently performed had more eutrophic species, while site harvested earliest (Site 5) had the least. These results are discussed with respect to how anthropogenic activities influence water quality, phytoplankton community structure, mangrove conservation and management.