Single Habitat Research Articles

Picturing Tropical Nature

The “tropics” have haunted the North Atlantic imperial imagination. The foliage, fruits, birds, animals, and peoples of these regions have satiated the appetites for exotica of physicians, naturalists, painters, curiosity seekers, and the sexually shy. The local inhabitants of the tropics, to be sure, have not been passive consumers of the various representations of their lands promiscuously put in circulation by the various European and the United States visitors. Nancy Leys Stepan has written a fascinating account of the history of this parallel (but not dialogical) set of representations, and her focus is Brazil in the nineteenth and early twentieth centuries.Nineteenth-century naturalists, travelers, and painters socialized North Atlantic audiences into a number of conventions about tropical fauna and flora that would later prove very difficult to dislodge. Illustrations crammed widely dispersed fauna and flora into a single habitat, and travelers emphasized adventure, the exotic, and their mastery over events and circumstance. Accounts of failure, contingency, and the mundane did not find a market. When Alfred Russell Wallace published his Narrative of Travels on the Amazon and the Rio Negro (1853), he made the conventions of the genre explicit, complaining of his having to travel long distances to find animals and plants that he had originally thought lived in the same habitat. The account emphasized Wallace’s boredom and failures. Moreover, the book lacked illustrations and tales of mastery and adventure. It was a commercial flop. By 1869, however, Wallace had learned his lesson. His The Malay Archipelago (1869) and Tropical Nature (1878) shamelessly exploited all the pictorial and narrative conventions Wallace had previously scorned. This time the books sold well.The European market craved images of freaks and sexually promiscuous racial inferiors in the tropics as well. The naturalist Louis Agazzi and the many practitioners of the new discipline of tropical medicine went out their way to satisfy these cravings. Stepan recounts Agazzi’s efforts to identify through photography the deleterious effects of mongrelization in Brazil and the various tropical racial types he encountered during his visit. This story of the science of race and imperialism is already well known (partly thanks to Stepan’s own previous writings), but the author’s account of the rise of tropical medicine as a discipline that managed to transform age-old European diseases into the exclusive pathologies of the tropical world is new and fascinating. Stepan shows how practitioners of the new discipline solely focused on discovering the cycles of “exotic” microscopic pathogens and on developing voyeuristic photographic archives of monstrous bodily parts of the individuals affected by these diseases.But, Stepan truly breaks new ground when she turns to how the Brazilian intelligentsia reacted to these North Atlantic representations of the tropics. She suggests, for example, that tropical medicine was not warmly received in Brazil, despite all the efforts of the distinguished local physician Carlos Chagas, because Chagas reproduced in his research the same voyeuristic taste for exotic monstrosities that had characterized North Atlantic practitioners. The Brazilian intelligentsia also questioned Agazzi’s racial typologies and saw tropical mongrelization as a boon, a source of national strength rather than degeneration. Finally, landscape architects such Roberto Burle Marx playfully and ironically manipulated European conventions of tropical flora to create gardens of great beauty.I have only one caveat with this book. Stepan overlooks nineteenth-century landscape painting in Brazil on the false premise that it was marginal and unimportant because the local intelligentsia never developed a taste for Natural Theology and thus a view of nature as sacred. Drawing on a single source, she wrongly concludes that only a handful (some 50) paintings and photographs of rural landscapes were produced in Brazil in the nineteenth century (pp. 216–17). Carlos Roberto Maciel Levy identified years ago some 600 extant landscape paintings by Antônio Parrerias (1860–1937) alone. In fact, a complete catalogue of nineteenth-century landscape painting in Brazil would most likely run into the thousands. For all its contributions, the reader will not find in Picturing the Tropics a study of how the dozens of Braizilian nineteenth-century landscape painters contested the North Atlantic representations of the “tropics.”

SCALE-DEPENDENT EFFECTS OF LANDSCAPE CONTEXT ON THREE POLLINATOR GUILDS

Most ecological processes and interactions depend on scales much larger than a single habitat, and therefore it is important to link spatial patterns and ecological processes at a landscape scale. Here, we analyzed the effects of landscape context on the distribution of bees (Hymenoptera: Apoidea) at multiple spatial scales with respect to the following hypotheses: (1) Local abundance and diversity of bees increase with increasing proportion of the surrounding seminatural habitats. (2) Solitary wild bees, bumble bees, and honey bees respond to landscape context at different spatial scales. We selected 15 landscape sectors and determined the percentage of seminatural habitats and the diversity of habitat types at eight spatial scales (radius 250-3000 m) by field inspections and analyses of vegetation maps using two Geographic Information Systems. The percentage of semi- natural habitats varied between 1.4% and 28%. In the center of each landscape sector a patch of potted flowering plants (four perennial and two annual species) was placed in the same habitat type, a grassy field margin adjacent to cereal fields. In all, 865 wild bee individuals and 467 honey bees were observed and an additional 475 individuals were caught for species identification. Species richness and abundance of solitary wild bees showed a close positive correlation with the percentage of seminatural habitats at small scales up to 750 m, whereas bumble bees and honey bees did not respond to landscape context at these scales. In contrast, honey bees were correlated with landscape context at large scales. The densities of flower-visiting honey bees even increased with decreasing proportion of seminatural habitats at a radius of 3000 m. We are not aware of any empirical studies showing contrasting foraging patterns related to landscape context at different spatial scales. We conclude (1) that local landscape destruction affects solitary wild bees more than social bees, possibly changing mutualistic plant-pollinator and competitive wild bees- honey bees interactions and (2) that only analyses of multiple spatial scales may detect the importance of the landscape context for local pollinator communities.

Lack of convergence in aquatic Anolis lizards.

Why convergent evolution occurs among some species occupying similar habitats but not among others is a question that has received surprisingly little attention. Caribbean Anolis lizards, known for their extensive convergent evolution among islands in the Greater Antilles, are an appropriate group with which to address this question. Despite the well-documented pattern of between-island convergence, some Greater Antillean anoles are not obviously part of the convergence syndrome. One example involves aquatic anoles--species that are found near to and readily enter streams-which have evolved independently twice in the Caribbean and also twice on mainland Central America. Despite being found in similar habitats, no previous study has investigated whether aquatic anoles represent yet another case of morphological convergence. We tested this hypothesis by collecting morphological data for seven aquatic anole species and 29 species from the six convergent types of Greater Antillean habitat specialists. We failed to find evidence for morphological convergence: the two Caribbean aquatic species are greatly dissimilar to each other and to the Central American species, which, however, may be convergent upon each other. We suggest two possible reasons for this lack of convergence in an otherwise highly convergent system: either there is more than one habitat type occupied by anoles in the proximity of water, or there is more than one way to adapt to a single aquatic habitat. We estimate that almost all of the 113 species of Greater Antillean anoles occupy habitats that are also used by distantly related species, but only 15% of these species are not morphologically similar to their distantly related ecological counterparts. Comparative data from other taxa would help enlighten the question of why the extent of convergence is so great in some lineages and not in others.

Scaling and habitat proportions in relation to bird diversity in managed boreal forests

The study of the relevant scales for use in landscape biodiversity management involves several difficulties, like small sample sizes at large scales and varying trends between species. I studied richness in a pool of 25 bird species in relation to the amounts and coverage proportions of four forest habitats over eight scales based on data from forty-two 10 km transects. By adding habitat amounts from the transects, the accumulated species pool flattened out when about 400 ha of older forest was included. Transect pooling gave plot sizes that reflected plots ranging in size 10–80 km 2, and the correlation’s between bird species richness and the proportions of two good and two poor habitats were calculated at eight scales. For three of the habitat proportions, respectively, species richness was significantly influenced only at the smallest scale (10 km 2), while for old forest also at 20 km 2. These regressions changed slopes (positive or negative) from the smaller to the larger scales for three of the habitats. However, in areas of 10 km 2 bird diversity was significantly predicted (positive or negative) by the proportion of any single habitat (suitable or poor), while in areas of 20–80 km 2 it was not, which may suggest that to reach comparably high levels of species richness in large areas, a mixture of several habitats is decisive. Thus, management of forest bird diversity may not be efficient over broad areas if the proportions of only one or a few habitats are used.

Inconsistency in short-term temporal variability of microgastropods within and between two different intertidal habitats

Small-scale temporal variation in abundances of fauna in marine soft sediments has long been recognised. Many studies on rocky intertidal shores have, however, focused on larger fauna in single habitats and have primarily examined relatively long time-scales. The implications of small-scale variability are frequently not adequately addressed in the studies of changes in fauna over longer time-scales. Without knowledge of the magnitude of variation at smaller scales, comparisons across longer time-scales may be confounded. In this study, the temporal variability of a number of co-existing species of microgastropods in patches of two different intertidal habitats (coralline turf and sediment) in Botany Bay, New South Wales, Australia, was measured using a nested, hierarchical sampling design incorporating temporal scales of weeks, 1 and 3 months. In addition to habitats, there were also spatial scales of metres between plots and 100s of metres between the locations. There was generally a lack of consistency in the trends of variance for the three temporal scales at the smallest spatial scale of plots. In addition, the different species, including those that were closely related, showed different patterns of variation, depending on the habitat and site. These data show the importance of incorporating adequate scales of sampling in different habitats when analysing the distribution and abundance of microbenthos in intertidal habitats.

Can habitat specialisation maintain a mosaic hybrid zone in marine bivalves?

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 245:157-170 (2002) - doi:10.3354/meps245157 Can habitat specialisation maintain a mosaic hybrid zone in marine bivalves? Nicolas Bierne1,*, Patrice David2, Aimé Langlade3, François Bonhomme1 1Laboratoire Génome, Populations, Interactions, CNRS UMR 5000, SMEL, 1 Quai de la Daurade, 34200 Sète, France 2CEFE - CNRS, 1919 route de Mende, 34293 Montpellier Cedex 5, France 3Laboratoire Conchylicole de Bretagne IFREMER, BP 26, 56470 La Trinité-sur-Mer, France *Present address: Centre for the Study of Evolution and School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom. Email: n-bierne@univ-montp2.fr ABSTRACT: Maintaining the integrity of differentiated genomes in marine organisms needs efficient isolation mechanisms, because planktonic larval dispersion provides contacts between taxa. Habitat specialisation is interesting in this respect, because it can both prevent interspecific crosses (each taxon reproduces in its own habitat) and eliminate hybrids (typically less fit than a parental taxon in each habitat). The contact zone between smooth-shelled mussels Mytilus edulis and M. galloprovincialis in Europe is a good example, as allozyme genotypes typical of both taxa seem to segregate into different habitats. However, allozymes may be selected directly and it is not known whether the same pattern can be extended to the whole genome. Here, we used 6 presumably neutral PCR markers to investigate habitat specialisation, focussing on the Bay of Quiberon, a small region in the midst of the contact zone between the 2 taxa. Confirming allozyme findings, our results indicate that habitat specialisation is apparent at the genomic scale, as M. edulis-like genotypes are found in sheltered or open-sea sites under freshwater influence, whereas M. galloprovincialis-like genotypes occupy exposed sites. Hybrid (or mixed) populations are found in open-sea or sheltered areas without freshwater influence. Therefore, habitat specialisation does contribute to the interspecific barrier. However, this mechanism seems insufficient to completely prevent the mixing of the 2 genomes, as mixed populations exist and provide opportunity for further hybridisation. Large gametic disequilibria within hybrid populations indicate the existence of restrictions to genetic exchange between the 2 taxa, even within a single habitat. Habitat-independent isolation mechanisms must, therefore, exist in addition. KEY WORDS: Habitat specialisation · Hybrid zone · Introgression · Mytilus edulis · Mytilus galloprovincialis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 245. Online publication date: December 18, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

LACK OF CONVERGENCE IN AQUATIC ANOLIS LIZARDS

Why convergent evolution occurs among some species occupying similar habitats but not among others is a question that has received surprisingly little attention. Caribbean Anolis lizards, known for their extensive convergent evolution among islands in the Greater Antilles, are an appropriate group with which to address this question. Despite the well-documented pattern of between-island convergence, some Greater Antillean anoles are not obviously part of the convergence syndrome. One example involves aquatic anoles—species that are found near to and readily enter streams—which have evolved independently twice in the Caribbean and also twice on mainland Central America. Despite being found in similar habitats, no previous study has investigated whether aquatic anoles represent yet another case of morphological convergence. We tested this hypothesis by collecting morphological data for seven aquatic anole species and 29 species from the six convergent types of Greater Antillean habitat specialists. We failed to find evidence for morphological convergence: the two Caribbean aquatic species are greatly dissimilar to each other and to the Central American species, which, however, may be convergent upon each other. We suggest two possible reasons for this lack of convergence in an otherwise highly convergent system: either there is more than one habitat type occupied by anoles in the proximity of water, or there is more than one way to adapt to a single aquatic habitat. We estimate that almost all of the 113 species of Greater Antillean anoles occupy habitats that are also used by distantly related species, but only 15% of these species are not morphologically similar to their distantly related ecological counterparts. Comparative data from other taxa would help enlighten the question of why the extent of convergence is so great in some lineages and not in others.Corresponding Editor: T. Smith

Soft-sediment benthic biodiversity on the continental shelf in relation to environmental variability

Soft-sediment macrobenthos data for the Norwegian continental shelf (61°N, 1 to 2°E) was used to examine species distributions, community structure and community differences, and how different measures of biodiversity are related to environmental variability. Water depth at 35 sites ranged from 115 to 331 m over a spatial sampling scale of ca. 45 km × 60 km, and there was consid- erable variation in sediment characteristics. Of a total of 508 recorded species, 39% were restricted to 1 or 2 sites, whereas only 3 species spanned the entire sampling area. Polychaetes were the most common and widespread taxonomic group; crustaceans and echinoderms were more restricted in their distributions than the other dominant groups. Whittaker's beta diversity measure ( βW, extent of change in species composition among sites) was highest for those groups with the highest proportion of restricted-range species. The number of shared species, the complementarity (biotic distinctness), and the Bray-Curtis similarity between all pairwise combinations of sites (3 beta diversity measures) were more strongly related to change in environment (notably depth, followed by median grain size and silt-clay content) than to spatial distance between sites. Likewise, a multivariate analysis (BIO- ENV) identified these factors as the major environmental variables influencing the faunal patterns, whereas univariate measures of diversity were not related to depth or median grain size. Univariate measures of diversity, beta diversity measures, and BIO-ENV analyses showed that molluscs, followed by polychaetes, were most highly related to environmental variables. In this study, alpha, beta and gamma diversity were higher than in a study of a single soft-sediment habitat type in the southern part of the Norwegian continental shelf.

A general model for simulating the effects of landscape heterogeneity and disturbance on community patterns

An individual-based, spatially explicit stochastic lattice model, CAPS, was designed to examine multiple processes responsible for spatial patterns of abundance and diversity of sessile species in heterogeneous landscapes. Species simulated by CAPS differ in habitat preferences (niche width), dispersal of propagules, and relative fecundity. The spatial distribution of habitat types are represented as heterogeneous gridded landscapes. The outcome of competition and establishment processes in successive generations is determined locally via a seed lottery. A series of 200 year-long simulations was performed to investigate the effects of variation in species characteristics and competition, landscape heterogeneity, and disturbance on patterns of species abundances. The outcome of competition was most sensitive to differences in fecundity between species, the spatial distribution of suitable habitat and the initial distribution of species. Species with a narrow niche were confined to a single habitat type and remained at or near their initialization sites. Broader niches resulted in increasing niche overlap and competition but enhanced species mobility, allowing abundance levels to approach expected values determined by map resources. Even so, initial distributions still affected the spatial patterns of species distributions at year 200. Disturbance regimes were simulated by varying the frequency, extent and spatial pattern of disturbances. Disturbance events removed species from affected sites but did not otherwise alter habitat characteristics. Results showed that disturbances may lead to a reversal in competition and establishment, dependent on species-specific differences in fecundity and dispersal. Although intermediate levels of disturbance frequency and extent increased the probability of species coexistence, the spatial pattern of disturbance played an unexpectedly important role in the tradeoff between dispersal and fecundity. The ability to simulate multiple factors affecting patterns of persistence, abundance and spatial distribution of species provided by CAPS allows new insight into the temporal and spatial patterns of community development.

When sources become sinks: migrational meltdown in heterogeneous habitats.

We consider the evolution of ecological specialization in a landscape with two discrete habitat types connected by migration, for example, a plant-insect system with two plant hosts. Using a quantitative genetic approach. we study the joint evolution of a quantitative character determining performance in each habitat together with the changes in the population density. We find that specialization on a single habitat evolves with intermediate migration rates, whereas a generalist species evolves with both very low and very large rates of movement between habitats. There is a threshold at which a small increase in the connectivity of the two habitats will result in dramatic decrease in the total population size and the nearly complete loss of use of one of the two habitats through a process of "migrational meltdown." In some situations, equilibria corresponding to a specialist and a generalist species are simultaneously stable. Analysis of our model also shows cases of hysteresis in which small transient changes in the landscape structure or accidental demographic disturbances have irreversible effects on the evolution of specialization.

Relationships between plant nitrogen economy and life history in three deciduous-forest herbs

1 We compared nitrogen (N) uptake and whole-plant N dynamics in three deciduous-forest herbs of contrasting life histories: the spring ephemeral Alliumtricoccum, the summergreen Violapubescens and the semievergreen Tiarellacordifolia. We predicted that differences in above-ground physiology would translate into differences in N acquisition and partitioning, such that nitrogen-use efficiency (NUE) would increase from Allium to Viola to Tiarella. 2 Patterns of N uptake were generally the opposite of our predictions. Allium had the lowest N uptake capacity in both laboratory and field experiments whereas roots of Tiarella had the highest specific N uptake capacity. 3 Viola was the only species in which the specific uptake capacity of roots was related to photosynthetic activity of leaves, both decreasing by a factor of two from spring to summer. In contrast, Tiarella consistently had the lowest photosynthetic capacity and the highest specific uptake capacity whereas Allium maintained substantial root uptake capacity throughout the summer when it had no photosynthetic activity. 4 There were no significant differences between species in overall NUE. However, there were differences in the components of NUE: nitrogen productivity (A) and mean residence time of N in the plant (MRT). Nitrogen productivity increased, and MRT decreased, from Allium to Viola to Tiarella. 5 In all three species, there was a balance between acquisition of N and building of biomass over the annual growth cycle, despite dramatic disjunctions between the tissue-specific rates of carbon and N acquisition in Allium and Tiarella. The variation in A and MRT we observed among co-occurring species of a single N-rich habitat was comparable with that observed by other researchers studying plants adapted to habitats of widely varying N availability.

Landscape Heterogeneity and Diurnal Raptor Diversity in Honduras: The Role of Indigenous Shifting Cultivation1

I studied the relationship between diurnal raptor diversity, density, and richness, and landscape heterogeneity in continuous primary forests and forests farmed by native Amerindians in the Río Plátano Biosphere Reserve of northeastern Honduras from January to June 1996 and 1997. I estimated landscape heterogeneity—the variability in naturally occurring and/or anthropogenic habitat mosaics—by mapping the extent and distribution of five human-modified and natural habitats in 24 1 km2 survey plots. I used the Shannon index to calculate landscape heterogeneity values for the respective plots based on the proportion of total area of each habitat within each plot. Diurnal raptor surveys from canopy-emergent viewpoints in these plots resulted in 137 observations of 18 species of raptors. Four species (Coragyps atratus, Ictinia plumbea, Leucopternis albicollis, and Buteo magnirostris) differed significantly in abundance among heterogeneity classes. Raptor diversity, density, and richness all increased directly with increasing landscape heterogeneity. Landscape heterogeneity was more important in explaining differences in raptor species diversity than the presence or extent of any single habitat or combination of habitats. In contrast to previous studies, my results indicate the importance of indigenous shifting cultivation in altering the naturally occurring patterns of habitat mosaics in lowland rain forest and its effect on bird species abundance and diversity in a rain forest ecosystem.

WHEN SOURCES BECOME SINKS: MIGRATIONAL MELTDOWN IN HETEROGENEOUS HABITATS

We consider the evolution of ecological specialization in a landscape with two discrete habitat types connected by migration, for example, a plant-insect system with two plant hosts. Using a quantitative genetic approach, we study the joint evolution of a quantitative character determining performance in each habitat together with the changes in the population density. We find that specialization on a single habitat evolves with intermediate migration rates, whereas a generalist species evolves with both very low and very large rates of movement between habitats. There is a threshold at which a small increase in the connectivity of the two habitats will result in dramatic decrease in the total population size and the nearly complete loss of use of one of the two habitats through a process of “migrational meltdown.” In some situations, equilibria corresponding to a specialist and a generalist species are simultaneously stable. Analysis of our model also shows cases of hysteresis in which small transient changes in the landscape structure or accidental demographic disturbances have irreversible effects on the evolution of specialization.Corresponding Editor: M. Whitlock

Photosynthetic nitrogen-use efficiency in evergreen broad-leaved woody species coexisting in a warm-temperate forest.

Photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) varies among species from different habitats and correlates with several ecological characteristics such as leaf life span and leaf mass per area. We investigated eight evergreen broad-leaved woody species with different leaf life spans that coexist in a warm-temperate forest. We determined photosynthetic capacity at ambient CO(2) concentration in saturated light, nitrogen concentration, and the concentration of ribulose-1,5-bisphosphate carboxylase (RuBPCase), a key enzyme of photosynthesis and the largest sink of nitrogen in leaves. Each species showed a strong correlation between photosynthetic capacity and RuBPCase concentration, and between RuBPCase concentration and nitrogen concentration. Photosynthetic capacity of leaves decreased with increasing leaf life span, whereas PNUE did not correlate significantly with leaf life span. There was a twofold variation in PNUE among species. This relatively small variation in PNUE is consistent with the argument that species that coexist in a single habitat maintain a similar PNUE. The two components of PNUE-photosynthetic rate per unit RuBPCase and RuBPCase per unit leaf nitrogen-were not significantly correlated with other leaf characteristics such as leaf life span and leaf mass per area. We conclude that differences in PNUE are relatively small among coexisting species and that differences in absolute amounts of photosynthetic proteins lead to differences in photosynthetic productivity among species.

The importance of aquatic margins to invertebrates in English chalk streams

Standardized kick-sweep samples of invertebrates were taken from three habitats - mid-channel gravel, Ranunculus and marginal vegetation - in six lowland chalk streams, on four sampling occasions between May 1996 and January 1997. Several types of marginal vegetation were sampled, including the stems and leaves of trailing terrestrial vegetation and semi-emergent marginal macrophytes. There was little difference in invertebrate community composition between the different marginal vegetation types, despite fine-scale differences in habitat architecture. The invertebrate communities in mid-channel gravel, Ranunculus and marginal vegetation were very different from each other over most of the year, particularly in spring and winter. Each habitat was characterised by a suite of invertebrates, reflecting the physical and biological differences between the habitats. Community diversity and equitability were greatest in the physically complex margins and least in the more simply structured Ranunculus. Invertebrate abundance per sample was greatest in Ranunculus. Approximately one half of all taxa in the chalk streams showed no significant preference for any single habitat. Of those taxa that significantly preferred one habitat, many more preferred marginal vegetation compared to either gravel or Ranunculus. Many taxa found throughout the investigation avoided gravel and Ranunculus, but very few taxa avoided marginal vegetation. Rare taxa also occurred more frequently in the margins. Marginal vegetation was used by invertebrates both as a favoured site of oviposition and as a conduit between the aquatic and terrestrial environments. Margins thus acted as a focus for reproduction and recruitment for chalk streams. The relative importance of marginal vegetation for stream invertebrate biodiversity and reproduction is high relative to other mid-channel habitats. More attention should be given to this habitat than has been in the past, particularly in the fields of stream conservation and restoration.

Implications of taxonomic resolution and sample habitat for stream classification at a broad geographic scale

Macroinvertebrate biological monitoring in Victoria, Australia, has required substantial resources over the past decade, and often results have taken years to reach water managers. Ways of reducing the time and effort required in this program were examined. The influence of taxonomic resolution and sample habitat on the classification and ordination of 165 stream sites in 27 catchments across Victoria was examined by progressively reducing the level of detail in the original data. Macroinvertebrate samples were collected from 2 habitats (riffle and edge) at each site. A 3rd data set was generated by amalgamating the individual habitats. These 3 habitat treatments were analyzed at family, genus, and species level, and a 4th taxonomic treatment was generated at species level including Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa only. All 12 data sets were analyzed using presence/absence data, and each was used to classify sites across Victoria into groups that were characterized using environmental variables. The Mantel test was used to compare the 12 analyses, and showed that each of the analyses produced similar patterns. A number of possible ways to reduce time and effort in broad-scale macroinvertebrate studies were evident: 1) single habitat sampling was sufficient for biological monitoring, 2) studies that require species-level discrimination may be able to reduce costs by identifying EPT taxa only, and 3) genus-level identifications offered no substantial advantage over family-level identifications. Overall, species-level identification appeared to be unnecessary for broad-scale monitoring programs and, in future, taxonomic effort could be reduced by identifying to family level only.

Fragments are not islands: patch vs landscape perspectives on songbird presence and abundance in a harvested boreal forest

The boreal mixed‐wood forest of northern Alberta. Canada is characterized by a mosaic of deciduous and coniferous forest patches. Recently, the deciduous portion of the forest was allocated for industrial logging. Widespread habitat loss and fragmentation may negatively affect birds and other wildlife. Most research on the effects of habitat loss on bird abundance has focussed on the forest as a patch or island in a matrix of non‐habitat, but some species of songbird may use both the forest patch and the matrix. We hypothesized that some species of songbird might be able to compensate for a loss of deciduous forest by moving into other habitat types (termed “habitat compensation”). We report on a replicated field investigation in which we assessed the response of songbirds to commercial timber harvest by first examining their abundance within deciduous forest only, and then adding the clearcuts and coniferous forest in the surrounding areas to the analysis for a broader, landscape view of the system. Bird communities in deciduous and coniferous habitats had significant overlap in species composition: there was less overlap between forest and clearcuts. The shift from patch‐centred to landscape sampling altered our interpretation of over half of the most common species' responses to logging in at least one year, suggesting that habitat compensation may have been occurring. However, significant variation in responses of species was observed between the two study areas. Our past reliance on island biogeographic and other single habitat approaches may be inappropriate for this system, and we stress that a broad, landscape view is required to properly assess and interpret species' responses to habitat loss and fragmentation.

Temporal patterns in coral assemblages on the Great Barrier Reef from local to large spatial scales

From 1992 to 1997 changes in cover of hard and soft corals and macro-algae were monitored using annual video transect surveys on the northeast flank of up to 52 reefs along most of the Great Barrier Reef (GBR). Trends in cover of hard corals, algae and soft corals were usually consistent among clusters of adjacent or nearby reefs. This consistency probably reflected the spatial scales of the effect of episodic disturbances caused by cyclones or crown-of-thorns starfish Acanthaster planci. Hence, our comprehensive monitoring of a single habitat provided an effective indicator of the status and trends on adjacent reefs. Moreover, we observed broad-scale patterns of increase and decline in coral cover that suggest that a 'patchwork mosaic' null model is a useful concept at scales of whole reefs and regions. At a large spatial scale (up to 10° of latitude), cover of hard corals within the NE slope habitat averaged 29% (± 12.4 standard deviation) and increased by 1.7% (±6.5) over 5 yr of surveys. Cover of soft corals and algae remained constant and averaged 14% (±12.4) and 41% (±16.6) respectively. Inner shelf, mid-shelf and outer shelf reefs in a 'recovery' phase increased their cover of hard coral at average annual rates of 2.6% (±3.0), 3.9% (±4.1) and 4.3% (±4.5) respectively. Year-to-year changes in cover of soft corals were typically smaller and less variable than changes in cover of hard corals or algae. There was no evidence of any shift to alternative stable states of assemblage composition.

On investigating local–regional species richness relationships

Most authors (e.g. Hugueny & Paugy 1995; Caley & Schluter 1997; Griths 1997; Oberdor€ et al. 1998) have concluded that local species richness is directly proportional to regional species richnessÐthe proportional sampling hypothesis (Cornell & Lawton 1992). Others (see Cornell & Karlson 1997) have found evidence for a levelling o€ in local richness as regional richness increases, consistent with the saturation of communities with species in some regions. Figure 1a shows the expected relations for the proportional sampling hypothesis and one version of the saturation curve. Here I consider the e€ects of inadequate sampling, inadequate pool identi®cation and statistical methodology (polynomial vs logarithmic and unconstrained vs constrained regression) on the shape of the local±regional relation detected, and examine other possible interpretations of a claimed non-interactive assemblage (Oberdor€ et al. 1998). The position of the intercept and the degree of curvature of the regression line are central to shape identi®cation. Inadequate sampling can a€ect where the local± regional relation crosses the ordinate. It is conceivable that local diversity at any given site could be zero when some species occur in the region. Whether or not this is the case will depend, in part, on the sample e€ort. Sampling e€ort that is inadequate but uniform across regions will move the intercept below zero by shifting the regression line to the right but should not a€ect the shape of the relation. If the degree of undersampling is a function of regional richness, the intercept might not pass through the origin (Fig. 1b). Changes in species rank-abundance patterns (or dispersion patterns) with regional richness could also a€ect the type of relation detected; for example, a shift from a geometric to a log-normal series pattern with increasing regional richness will result in a smaller fraction of the assemblage being sampled. A trend of reduced dominance with increasing species richness, which is plausible (Gray 1987; Whittaker 1975), will increase the chance of falsely detecting a saturating relationship. Correctly identifying regional pools can be problematic; for example Oberdor€ et al. (1998) de®ned their regional pool in ecological terms, noting that `a regional but ecologically based species richness would include only those species that are able to maintain populations within the sites studied'. The ecological pools were identi®ed from a more geographically widespread correspondence analysis (Verneaux 1981) which divided a species continuum into nine categories. How the sample sites were related to Verneaux's categories was not explained. This step is important because identifying an assemblage as indicative of, for example, Verneaux's metarhithron rather than the adjacent mesorhithron category would increase the regional pool size from 10 to 15 (i.e. by 50%) or if only the two most common abundance classes were used from 5 to 9 (by 80%). Moreover the 10 species found by Oberdor€ et al. (1998) do not appear to come from a single habitat because they divide into two ecological assemblages, one characteristic of relatively fastowing conditions (salmon, trout, minnow, bullhead, stoneloach) and the other of much slower ows (gudgeon, roach, chub and dace). Misidenti®cations of pools will shift the intercept up or down, depending on whether they have been underor overestimated: incorrect inclusion seems more likely than exclusion, favouring subzero intercepts. Two methods have been used to test the shape of the local±regional relation. 1. Fit a second-order polynomial regression, the lower order, linear, model being used to test for linearity if the second-order term is not signi®cant (Hawkins & Compton 1992). Some authors (Hugueny & Paugy 1995; Caley & Schluter 1997; Cornell & Karlson 1997; Oberdor€ et al. 1998) have omitted the constant, thereby constraining the line to pass through the origin, because `when regional diversity is zero, so too is local diversity' (Caley & Schluter 1997). It is correct that local richness must, by de®nition, be equal to or less than regional richness but the line need not pass through the origin, for the reasons outlined above. Accordingly when using polynomial regression the intercept a should be R 0 but not necessarily Correspondence: University of Ulster Freshwater Laboratory, Traad Point, Ballyronan, Co. Londonderry, UK, BT45 6LR. E-mail: D.Griths@ulst.ac.uk Journal of Animal Ecology 1999, 68, 1051±1055

An Efficient Sampling Survey Design to Estimate Pink Shrimp Population Abundance in Biscayne Bay, Florida

We developed an efficient sampling design-based approach using fishery-independent surveys to estimate population abundance of pink shrimp Penaeus duorarum over time in Biscayne Bay, Florida. We initially implemented quarterly stratified random sampling (StRS) using nine habitat strata and determined that average pink shrimp density (numbers/m2) was highest in late fall and lowest in spring and late summer. Coefficient of variation of the quarterly surveys, expressed as percent standard error/mean density, ranged from 5.8% to 14.3%. We found StRS to be more efficient (i.e., with lower variance) than simple random sampling (SRS) in most seasons. Statistical analyses suggested that pink shrimp densities were dependent on the biophysical habitat variables of bottom substrate, depth, and salinity. We also noted ontogenetic shifts in these relationships that were particularly pronounced at the onset of sexual maturation. Poststratification analysis was used to further evaluate several alternative habitat-based sampling schemes. Results showed that a five-strata composite design that used all three habitat variables was similar in performance, but less complex, than the original nine-strata design. In addition, the composite design outperformed both SRS and all other StRS designs indexed on single habitat variables. The new five-strata composite design was implemented in late summer 1997 and achieved a significant reduction in coefficient of variation compared with the late summer 1996 survey. This new design did not perform as well as expected in late fall 1997, which we attribute to a mismatch between our seasonal sample allocation strategy and the timing of pink shrimp recruitment into Biscayne Bay in 1997. Finally, we show how statistical sampling designs that use stratifications based on relevant habitat covariates can yield high-precision abundance estimates at low costs and provide a robust quantitative methodology for identifying habitat essential to fisheries production.