Effects of habitat complexity on benthic assemblages in a variable environment

1. Habitat complexity is thought to exert a significant influence on ecological communities, but its operation under variable natural conditions is not well understood, particularly in freshwater. To elucidate the role of habitat complexity, in particular the fractal structure of surface irregularity, in a stream system, field colonisation experiments were conducted at three times of year (summer, winter and spring) using natural substrates with different levels of fractal dimension in a small coastal mountain stream of southern Japan. 2. In the winter experiment, comparison was also made between the standard (control) treatment and the resource‐preconditioning treatment whereby experimental plates were conditioned in the natural stream environment to allow the accumulation of potential food resources (algae and detritus) for 1 month prior to the experiment. 3. Species abundance patterns observed at different times of year showed little systematic variation with levels of habitat complexity but largely followed the patterns expected from, or lying in between, the Random Assortment model and the random fraction model. 4. Taxon richness and density increased with habitat complexity in all seasons except for density in spring. Different taxa showed different patterns of change with habitat complexity, which also varied with seasons. Biomass of invertebrates showed no systematic trend with an increase in habitat complexity. 5. Chlorophyll‐a concentrations tended to be lower in more complex habitats, particularly in summer. In contrast, fine particulate organic matter (FPOM) tended to increase with habitat complexity. However, the relationship between these potential food resources and invertebrate assemblages remain unclear. 6. While there were no significant differences in taxon richness and biomass of invertebrates between the resource‐preconditioning and the control treatment, density was higher in the former than in the latter. The abundance of relatively large, surface‐dwelling animals showed more marked temporal variation over the entire period of colonisation in the resource‐preconditioning treatment than in the control treatment. 7. Body size of invertebrates tended to decline with fractal complexity, indicating that crevice sizes could affect habitat use by benthic animals of different sizes. In addition, body size was larger in the resource‐preconditioning treatment than in the control treatment, suggesting that body size in invertebrate assemblages was controlled by a mixture of factors. Thus, the present study demonstrates that habitat structure affects benthic invertebrate assemblages in a complex manner.     

The effects of habitat complexity and hydraulic conditions on the establishment of benthic stream macroalgae

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The stability–diversity relationship in stream macroinvertebrates: influences of sampling effects and habitat complexity

1. Theory predicts that the stability of a community should increase with diversity. However, despite increasing interest in the topic, most studies have focused on aggregate community properties (e.g. biomass, productivity) in small‐scale experiments, while studies using observational field data on realistic scales to examine the relationship between diversity and compositional stability are surprisingly rare. 2. We examined the diversity–stability relationship of stream invertebrate communities based on a 4‐year data set from boreal headwater streams, using among‐year similarity in community composition (Bray–Curtis coefficient) as our measure of compositional stability. We related stability to species richness and key environmental factors that may affect the diversity–stability relationship (stream size, habitat complexity, productivity and flow variability) using simple and partial regressions. 3. In simple regressions, compositional stability was positively related to species richness, stream size, productivity and habitat complexity, but only species richness and habitat complexity were significantly related to stability in partial regressions. There was, however, a strong relationship between species richness and abundance. When abundance was controlled for through re‐sampling, stability was unrelated to species richness, indicating that sampling effects were the predominant mechanism producing the positive stability–diversity relationship. By contrast, the relationship between stability and habitat complexity (macrophyte cover) became even stronger when the influence of community abundance was controlled for. Habitat complexity is thus a key factor enhancing community stability in headwater streams.     

Wasp community responses to habitat complexity in Sydney sandstone forests

Abstract Habitat structure and complexity affect the diversity and composition of fauna in a number of systems. We investigated patterns in wasp species richness, abundance and composition and also their associations with habitat complexity in Sydney sandstone forests, Australia. Pitfall and flight‐intercept traps collected dissimilar wasp assemblages. High complexity habitats supported greater abundance and species richness and a dissimilar composition of pitfall‐trapped wasps to low complexity habitats. Soil moisture, tree canopy cover, ground herb cover and shrub canopy cover all had significant positive associations with the species richness of pitfall‐trapped wasps. Although the five most abundant families of wasps we trapped are endoparasitoids of other arthropods, they showed a variety of preferences for habitat variables. The mechanisms driving associations between habitat complexity and patterns in wasp communities may also provide a basis for understanding factors influencing the regulation of arthropod assemblages by wasps in agricultural and natural landscapes.     

Effects of substratum stability on diversity of stream invertebrates during baseflow at two spatial scales

1. The effects of substratum stability on the diversity of stream invertebrates were assessed at two spatial scales in a Japanese stream during baseflow, from May to June 1998. Deposition and erosion were examined separately as distinct elements of substratum stability by a newly developed method using small steel pins. Stream invertebrates were sampled after 28 days of measurement of substratum stability. We also measured physical environmental variables, current velocity and depth, and food resource parameters including periphyton and particulate organic matter (POM) standing crops.
2. At the scale of the habitat patch, the effects of substratum stability on invertebrates were overwhelmed by those of POM standing crop. Moreover, higher taxon richness at high abundance may simply result from a higher likelihood of more taxa being included in samples. Therefore, this small scale revealed no role for substratum stability in explaining spatial pattern of community diversity.
3. At the reach scale ( n =10), taxon richness and evenness peaked at an intermediate level of deposition, whereas invertebrate abundance did not show any significant relationship. This result, and the pattern of relative abundance of common taxa, implies that the diversity of stream invertebrates was determined by subtle substratum movements and by the habitat preference of each taxon.
4. The difference in the determinant of community parameters between the habitat patch and the reach affirm the importance of a cross-scale analysis to choose an appropriate spatial scale for investigating the community structure of stream invertebrates. Prominent effects of substratum stability, particularly the deposition of substratum particles, during baseflow suggest that subtle and constant movement of small substratum particles can contribute to determine the diversity of stream invertebrates.     

The effect of plant density on epiphytic macroinvertebrates associated with a submerged macrophyte,Lagarosiphon ilicifolius Obermeyer,in Lake Kariba,Zimbabwe

The effect of variations in the density of a submerged macrophyte, Lagarosiphon ilicifolius, on epiphytic macroinvertebrate community structure in the shallow waters of a sheltered bay of Lake Kariba were investigated. The body size class distributions of a mayfly, Cloeon (Ephemeroptera: Baetidae), and the damselfly family, Coenagrionidae, were also assessed with respect to variation in vegetation density. Macroinvertebrates were sampled from low-, moderate- and high-density beds of L. ilicifolius. There were no significant differences in individual taxon and total macroinvertebrate abundances, macroinvertebrate richness and diversity with respect to vegetation density. In all three density categories the functional feeding group (FFG) composition was dominated by collector-gatherers and collector-filterers. The abundance of the two FFGs did not change significantly within each, as well as among, the three vegetation-density categories (ANOVA, p > 0.05). The largest size class of Cloeon occurred only in high-density beds, whereas the largest coenagrionid individuals were obtained from low- and moderate-density beds and were absent from high-density beds. The results suggest that variation in the density of Lagarosiphon does not affect epiphytic macroinvertebrate community structure, but does affect body-size distributions of macroinvertebrate taxa, probably by affecting predator-prey interactions.     

Does predator abundance influence species diversity of equilibrium macroinvertebrate assemblages in spring fens?

1. Predation may significantly control number and density of coexisting species. The effects of predation on species diversity have traditionally been tested in experiments and theoretical models of simple trophic systems. In complex natural ecosystems, however, disentangling multiple sources of variation is difficult. In groundwater-fed environments, a significant effect of predation can be expected due to the relatively stable environmental conditions; however, it has never been properly examined.
2. We analysed species diversity and total abundance of macroinvertebrate assemblages in 48 Western Carpathian spring fens, separately for whole sites and mesohabitat/season, and partitioned the effects of predation intensity from those of environmental variables in robust models using a bootstrapping technique. We verified our results by accounting for taxa resistant to predation.
3. The assumption that predation-mediated coexistence of species is the main mechanism responsible for the relatively species-rich assemblages in the Western Carpathian spring fens was not supported. However, predation may significantly influence abundance of non-predatory species and, under some conditions, it may contribute to explaining patterns in species diversity.
4. The effect of predation did not differ between the mesohabitats with different stability. However, we found higher environmental control in spring and a stronger effect of predators in autumn, which suggests that different mechanisms influence fen assemblages in different seasons.
5. Our study provides a new robust approach how to test the effect of predation on natural macroinvertebrate assemblages. The importance of predation was lower than expected in equilibrium assemblages but it may vary in time.

     

Species diversity and abundance of small mammals in Nechisar National Park,Ethiopia

Species diversity and abundance of small mammals were studied in Nechisar National Park, Ethiopia, during August 2008 – March 2009. Twenty species of rodents and four species of insectivores were recorded from the study area. Mastomys natalensis (17.37%), Arvicanthis dembeensis (17.09%), Mastomys erythroleucus (8.90%), Stenocephalemys albipes (8.76%), Arvicanthis niloticus (8.19%), Acomys cahirinus (7.34%), Lemniscomys striatus (6.92%), Gerbilliscus nigricauda (6.21%), Grammomys dolichurus (3.67%), Gerbilliscus robusta (2.12%), Mus proconodon (1.98%), Mus mahomet (1.41), Dendromus melanotis (1.27%), Arvicanthis abyssinicus (1.13%), Mus musculus (0.99%), Praomys fumatus (0.85%), Xerus erythropus (0.85%), Lemniscomys barbarus (0.71%), Mus tenellus (0.71%) and Otomys typus (0.28%) were the rodents and their respective relative abundance in the study area. Crocidura olivieri (1.55%), Crocidura fumosa (0.85%), Crocidura bicolor (0.57%) and Elephantulus rufescens (0.28%) were the insectivores recorded with their respective relative abundance. Mastomys natalensis was the most abundant and O. typus and E. rufescens were the least (two each). Diversity of small mammals ranged from 2.299 to 2.625 with an average of 2.412. The highest small mammal diversity was in grasslands and the lowest was in Lake Chamo shore. Small mammal density varied from 5 to 43 ha^?1 and biomass varied from 244 to 2559 g ha^?1 with significant changes in relation to seasons and habitats.     

Reappraising the effects of habitat structure on river macroinvertebrates

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Effects of habitat complexity and predator exclusion on the abundance of juvenile red snapper

Predator exclusion and habitat complexity factors that may affect juvenile red snapper Lutjanus campechanus habitat selection were examined in field and laboratory experiments. A significant predator exclusion effect was detected. Uncaged shell habitats showed significantly lower numbers of age 0 year red snapper, and both uncaged shell and block-shell habitats showed significantly lower numbers of age 1 year red snapper compared with caged habitats ( P < 0·001). Habitat complexity also affected age 0 year red snapper, as mean abundance significantly decreased with decreased habitat complexity ( P < 0·001). In the laboratory, age 0 year red snapper association with complex habitats significantly increased with exposure to a predator Gulf flounder Paralichthys albigutta ( P < 0·001). This study showed that predator exclusion and habitat complexity were significant factors that affected the abundance of juvenile red snapper in nursery areas of the northern Gulf of Mexico. Predation may affect juvenile red snapper abundance directly through mortality and indirectly by influencing habitat selection.     

Effects of habitat complexity,dominance and personality on habitat selection: Ideal despotic cichlids

Habitat structure can impede visibility and movement, resulting in lower resource monopolization and aggression. Consequently, dominant individuals may prefer open habitats to maximize resource gain, or complex habitats to minimize predation risk. We explored the role of dominance on foraging, aggression and habitat choice using convict cichlids (Amatitlania nigrofasciata) in a two‐patch ideal free distribution experiment. Groups of six fish of four distinct sizes first competed for shrimp in one‐patch trials in both an open and complex habitat; half the groups experienced each habitat type first. Following these one‐patch trials, each group then chose between habitat types in a two‐patch trial while competing for food. Finally, each fish underwent an individual behavioural assessment using a battery of “personality” tests to determine if behaviour when alone accurately reflected behaviour within a social context. In the one‐patch trials, dominant fish showed similar food consumption between habitats, but chased more in the complex habitat. In the two‐patch choice trials, dominants preferred and defended the complex habitat, forming an ideal despotic distribution with more than half the fish and competitive weight in the open habitat. Within the groups, individual fish differed in foraging and chasing, with repeatabilities of 0.45 and 0.23 across all treatments. Although a higher foraging rate during the individual assessment predicted foraging rate and use of the complex habitat during the group trials, aggression and boldness tests were not reflective of group behaviour. Across groups, heavier dominants and those with higher foraging rate in the open habitat used the open habitat more, suggesting that both risk and energetic state affect habitat preference in dominant convict cichlids.     

无脊椎动物金属硫蛋白(MTs)多样性及其生态服务功能

金属硫蛋白（MTs）是一类低分子量、半胱氨酸含量异常丰富的金属结合多肽,自从20世纪70年代中期发现海洋无脊椎动物MTs以来,MTs已被证明广泛存在于无脊椎动物的各个类群之中。无脊椎动物物种间的金属硫蛋白存在着显著差异,研究无脊椎动物MTs多样性并揭示其生态服务功能,在理论与实践上都至关重要。本文分析了无脊椎动物MTs的多样性：结合金属元素多样性、同形体及其变体的蛋白质遗传多样性和生态服务功能多样性,并讨论了 MTs的三个生态服务功能：MTs对重金属解毒和调节作用、MTs作为环境监测的生物标志物、MTs的环境重金属污染净化功能及其在环境污染治理中的作用。     

Disturbance history influences the distribution of stream invertebrates by altering microhabitat parameters: a field experiment

1. We investigated the effects of local disturbance history and several biotic and abiotic habitat parameters on the microdistribution of benthic invertebrates after an experimental disturbance in a flood‐prone German stream. 2. Bed movement patterns during a moderate flood were simulated by scouring and filling stream bed patches (area 0.49 m²) to a depth of 15–20 cm. Invertebrates were investigated using ceramic tiles as standardized substrata. After 1, 8, 22, 29, 36 and 50 days, we sampled one tile from each of 16 replicates of three bed stability treatments (scour, fill and stable controls). For each tile, we also determined water depth, near‐bed current velocity, the grain size of the substratum beneath the tile, epilithic algal biomass and standing stock of particulate organic matter (POM). 3. Shortly after disturbance, total invertebrate density, taxon richness and density of the common taxa Baetis spp. and Chironomidae were highest in stable patches. Several weeks after disturbance, by contrast, Baetis spp. and Hydropsychidae were most common in fill and Leuctra spp. in scour patches. The black fly Simulium spp. was most abundant in fill patches from the first day onwards. Community evenness was highest in scour patches during the entire study. 4. Local disturbance history also influenced algal biomass and POM standing stock at the beginning of the experiment, and water depth, current velocity and substratum grain size throughout the experiment. Scouring mainly exposed finer substrata and caused local depressions in the stream bed characterized by slower near‐bed current velocity. Algal biomass was higher in stable and scour patches and POM was highest in scour patches. In turn, all five common invertebrate taxa were frequently correlated with one or two of these habitat parameters. 5. Our results suggest that several ‘direct’ initial effects of local disturbance history on the invertebrates were subsequently replaced by ‘indirect’ effects of disturbance history (via disturbance‐induced changes in habitat parameters such as current velocity or food).     

Restoration for variability: emergence of the habitat diversity paradigm in terrestrial ecosystem restoration

Ecosystem restoration implies focusing on multiple trophic levels and ecosystem functioning, yet higher trophic levels, that is, animals, are less frequently targeted by restoration than plants. Habitat diversity, the spatial heterogeneity between and within habitat patches in a landscape, is a well‐known driver of species diversity, and offers possible ways to increase species diversity at multiple trophic levels. We argue that habitat diversity is central in whole‐ecosystem restoration as we review its importance, provide a practical definition for its components, and propose ways to target it in restoration. Restoration targeting habitat diversity is used commonly in aquatic ecosystems, mostly to increase the physical diversity of habitats, meant to provide more niches available to a higher number of animal species. To facilitate the uptake of habitat diversity in terrestrial ecosystem restoration, we distinguish between compositional and structural habitat diversity, because different animal groups will respond to different aspects of habitat diversity. We also propose four methods to increase habitat diversity: varying the starting conditions to obtain divergent successional pathways, emulating natural disturbances, establishing keystone structures, and applying ecosystem engineer species. We provide two case studies to illustrate how these components and methods can be incorporated in restoration. We conclude that targeting habitat diversity is a promising way to restore habitats for a multitude of species of animals and plants, and that it should become mainstream in restoration ecology and practice. We encourage the restoration community to consider compositional and structural habitat diversity and to specifically target habitat diversity in ecosystem restoration.     

Pulling the threads together: habitat diversity

The dependence of fungi on host and habitat is emphasized and the reticulate pattern of the interactions explored. Habitat diversity, often defined by the vascular plant element, vertebrate and invertebrate associations, and non-phanerogamic mutualisms are considered. The role of man especially in changes in habitat availability is stressed. Infraspecific variability is mentioned. The diversity of habitats is as much a part of the Rio Convention as molecular, cellular and organismal variation.     

The shallow water gobiid assemblage of the Venice Lagoon: abundance, seasonal variation and habitat partitioning

The gobiid assemblage of the Venice Lagoon shallow waters was investigated by means of a semi‐quantitative standardized sampling (using a small beach seine), stratified into five main types of shallow subtidal habitats and conducted on a seasonal basis during 1 year. The degree of overlap in resource utilization among six coexisting goby species was assessed, along both the time axis, by analysing the seasonal variation in abundance and reproductive status (as revealed by the gonado‐somatic index) and the habitat axis, by comparing species abundance across different habitat types and controlling for the effects of some abiotic factors. Smaller species, and especially the marbled goby Pomatoschistus marmoratus , dominated the local assemblage. Although the cycle of shallow water colonization and seasonal variation in total abundance were basically similar, species showed differences in timing of reproduction and recruitment, as well as in habitat preference. The larger species belonging to the genera Gobius and Zosterisessor tended to overlap their habitat use, being more abundant in seagrass habitats than in the unvegetated habitats, whereas the smaller species belonging to the genera Knipowitschia and Pomatoschistus avoided seagrasses, preferring in most cases mud flats and salt marsh creeks. Within these two groups of species some further slight differences in species habitat preference, relationship with abiotic factors and reproductive ecology could be detected. Results are discussed in the light of both ecological mechanisms underlying coexistence of closely related species and the current knowledge of the phylogeny of Mediterranean gobies.     

Effects of structural diversity and identity of patches of habitat on diversity of benthic assemblages

A fundamental problem in ecology, regardless of habitat or system, is understanding the relationship between habitats and assemblage of organisms. It is commonly accepted that differences in composition and surrounding landscape of habitats affect the diversity of assemblages, although there is not much empirical evidence because of difficulties of manipulating structure in many habitats. These relationships were examined experimentally, using habitats of artificial turfs that are colonized by diverse assemblages of gastropods. Each habitat was made of nine sub‐habitats, which were sampled individually to allow tests of hypotheses about the effect of type of habitat and the influence of other adjacent sub‐habitats on the colonizing assemblage. Turf habitats were deployed for 8 weeks on a rocky shore after which they were collected and the colonizing assemblages of gastropods sampled. Independently of the types of turfs combined to form different habitats, there were more species where there was more than one type of component in a habitat (i.e. structural diversity). The type of habitat (i.e. structural identity) itself had little or no influence on the colonizing assemblage. The number of species colonizing short‐sparse and short‐dense turfs was influenced by which type of habitat was adjacent. Thus, when units of one type (e.g. short‐sparse turf) were added to a patch of habitat of long‐sparse turfs, the number of species in short‐sparse turfs was greater than in patches of the same type. This also increased total number of taxa in the whole patch of habitat. These results show how diversity of gastropods colonizing heterogeneous patches of habitat is influenced not only by the number of types of sub‐habitats, but also by interactions with surrounding sub‐habitats. These findings reiterate the importance of investigating the role of structure of habitats and of their surrounding landscapes across different systems, irrespective of their size or associated assemblages of organisms.