Scales and costs of habitat selection in heterogeneous landscapes

Summary Two scales of habitat selection are likely to influence patterns of animal density in heterogeneous landscapes. At one scale, habitat selection is determined by the differential use of foraging locations within a home range. At a larger scale, habitat selection is determined by dispersal and the ability to relocate the home range. The limits of both scales must be known for accurate assessments of habitat selection and its role in effecting spatial patterns in abundance. Isodars, which specify the relationships between population density in two habitats such that the expected reproductive success of an individual is the same in both, allow us to distinguish the two scales of habitat selection because each scale has different costs. In a two-habitat environment, the cost of rejecting one of the habitats within a home range can be expressed as a devaluation of the other, because, for example, fine-grained foragers must travel through both. At the dispersal scale, the cost of accepting a new home range in a different habitat has the opposite effect of inflating the value of the original habitat to compensate for lost evolutionary potential associated with relocating the home range. These costs produce isodars at the foraging scale with a lower intercept and slope than those at the dispersal scale.Empirical data on deer mice occupying prairie and badland habitats in southern Alberta confirm the ability of isodar analysis to differentiate between foraging and dispersal scales. The data suggest a foraging range of approximately 60 m, and an effective dispersal distance near 140 m. The relatively short dispersal distance implies that recent theories may have over-emphasized the role of habitat selection on local population dynamics. But the exchange of individuals between habitats sharing irregular borders may be substantial. Dispersal distance may thus give a false impression of the inability of habitat selection to help regulate population density.     

Ecosystem Linkages Between Lakes and the Surrounding Terrestrial Landscape in Northeast Iceland

Despite a recent emphasis on understanding cross-habitat interactions, few studies have examined the ecological linkages between lakes and surrounding terrestrial habitats. The current paradigm of land–lake interactions is typically unidirectional: the view is that nutrients and matter are transported downslope from the surrounding watershed to their ultimate lacustrine destination. Emergent aquatic insects, which spend their larval stages in lake sediments and emerge as adults to mate over land, can act as vectors of material, energy and nutrients from aquatic to terrestrial habitats. In this study, we document a gradient of midge (Diptera: Chironomidae) infall rates into terrestrial habitats (measured as g dw midges m^?2 d^?1) surrounding eight lakes in Northern Iceland (≈66°N latitude). Lakes ranged from having virtually no midge infall (for example, Helluvaðstjörn, 0.03 g m^?2 d^?1) to extreme levels (for example, Mývatn, 19 g m^?2 d^?1) with abundances of midges decreasing logarithmically with distance from shore. Annual midge input rates are estimated as high as 1200–2500 kg midges ha^?1 y^?1. As midges are approximately 9.2% total N, this can result in a significant fertilization effect of terrestrial habitats with consequences for plant quality and community structure. In addition, we used naturally-occurring δ¹³C and δ¹⁵N isotopes to examine food web structure and diet sources of terrestrial arthropod consumers surrounding lakes with differing amounts of midge input. Terrestrial arthropods showed increased utilization of aquatic-derived (that is, midge) C relative to terrestrial sources as midge infall increased. This pattern was particularly pronounced for predators, such as spiders and opiliones, and some detritivores (Collembola). These findings suggest that, despite being largely ignored, aquatic-to-terrestrial linkages can be large and midges can fuel terrestrial communities by directly serving as resources for predators and decomposers.     

Variability between Scales: Predictors of Nomadism in Birds of an Australian Mediterranean-climate Ecosystem

Nomadism in animals is a response to resource distributions that are highly variable in time and space. Using the avian fauna of the Mediterranean-climate region of southcentral Australia, we tested a number of variables to determine if they predicted nomadism. These variables were species body mass, the distance in body mass terms to the edge of a body mass aggregation, and diet (for example, seeds, invertebrates, nectar, or plants). We utilized two different classifications of the avifauna that diverged in their definition of nomadic to build two different predictive models. Using both classifications, distance to the edge of a body mass aggregation was found to be a significant predictor of nomadism. There was also evidence that nomads tend to feed on nectar and tend to be large. The significance of the variables body mass and diet (nectar) may reflect the greater energy requirements of large birds and the inherent variability of nectar as a food source. The significance of the variable distance to the edge of a body mass aggregation provides further evidence of inherent variability in resources between domains of scale. The edges of body mass aggregations are hypothesized to be areas of increased resource variability that reflect the transition from one scale of landscape pattern to another. Received 14 November 2000; accepted 27 June 2001.     

Frugivores and seed dispersal: mechanisms and consequences for biodiversity of a key ecological interaction

The 5th Symposium on Frugivores and Seed Dispersal, held in Montpellier (France), 13-18 June 2010, brought together more than 220 researchers exemplifying a wide diversity of approaches to the study of frugivory and dispersal of seeds. Following Ted Fleming and Alejandro Estrada's initiative in 1985, this event was a celebration of the 25th anniversary of the first meeting in Veracruz, Mexico. Frugivory and seed dispersal are active research areas that have diversified in multiple directions since 1985 to include evolution (e.g. phylogenetic diversity and dispersal adaptations), physiology (e.g. sensory cues and digestion), landscape ecology (movement patterns), molecular ecology (e.g. gene flow, genetic diversity and structure), community ecology (e.g. mutualistic interaction networks) and conservation biology (effects of hunting, fragmentation, invasion and extinction), among others. This meeting provided an opportunity to assess conceptual and methodological progress, to present ever more sophisticated insights into frugivory in animals and dispersal patterns in plants, and to report the advances made in examining the mechanisms and consequences of seed dispersal for plants and frugivores.     

The predatory Chironomidae of an iron-rich stream: feeding ecology and food web structure

Abstract. 1. Three species of Tanypodinae (Chironomidae) were found in an acid and iron-rich stream in southern England. Maximum abundance was achieved in summer and they were sparse at other times. Individuals were aggregated on the stream bed and were overrepresented in accumulations of leaf litter.
2. The diets of all three species consisted of a mixture of prey (prominently detritivorous chironomid larvae) and detritus. More detritus and fewer prey were taken in winter than in summer.
3. When comparing large tanypod species with small and, intraspecifically, late instars with early, the proportion of guts containing prey increased with increasing body size.
4. Stonefly larvae were more prominent in the diet of Zavrelimyia barbatipes (Kieffer) in summer than in winter but for the other two species the reverse was true. A bigger proportion of Trissopelopia longimana (Staeger) guts contained prey in early summer than in August whereas more Macropelopia goetghebueri (Kieffer) guts contained prey in August. This was apparently a consequence of seasonal differences in the distribution of body size among the populations of these two species.
5. The stream contains two further common predators, Plectrocnemia conspersa (Curtis) and Sialis fuliginosa Pict. These are important predators of tanypod larvae but might also compete with them since they severely deplete populations of prey taken in common.
6. Analysis of the food-web in Broadstone Stream reveals remarkably high values of connectance (C and C_max) and of species richness times connectance (SC_max). Such characteristics are theoretically associated with fragile and dynamically unstable food webs, and may be found in 'constant' environments. There is also an apparently unusual prevalence of omnivory in the community.     

Biodiversity and Conservation of Diptera in Heterogeneous Land Mosaics: A Fly's Eye View

Classical landscape ecology views spatial heterogeneity of habitats at relatively large 'human scales', and it is at such scales that most decisions of land management and nature conservation are made. The present paper makes use of a wider range of spatial scales to examine land mosaics from the 'fly point of view'. Taking examples from the Diptera faunas of mountainous land mosaics, it is demonstrated that: (i) large scale, 'patch content' landscape management has a direct bearing on Diptera community structure, (ii) borders between large scale patches are not necessarily perceived by flies (or other insects) in the same way as we perceive them, (iii) border complexity between patches at any scale may be as important as patch content as an axis of habitat definition. In this sense, 'border' is not to be confused with 'edge effects'. It is concluded that attention to both patch content and patch border complexity of land mosaics, viewed at the relevant spatial scales, is necessary for future successful conservation of Diptera biodiversity and for the efficient use of these insects in environmental assessment studies.     

Tangled webs: reciprocal flows of invertebrate prey link streams and riparian zones

1. Streams and their adjacent riparian zones are closely linked by reciprocal flows of invertebrate prey. We review characteristics of these prey subsidies and their strong direct and indirect effects on consumers and recipient food webs. 2. Fluxes of terrestrial invertebrates to streams can provide up to half the annual energy budget for drift‐feeding fishes such as salmonids, despite the fact that input occurs principally in summer. Inputs appear highest from closed‐canopy riparian zones with deciduous vegetation and vary markedly with invertebrate phenology and weather. Two field experiments that manipulated this prey subsidy showed that it affected both foraging and local abundance of stream fishes. 3. Emergence of adult insects from streams can constitute a substantial export of benthic production to riparian consumers such as birds, bats, lizards, and spiders, and contributes 25–100% of the energy or carbon to such species. Emergence typically peaks in early summer in the temperate zone, but also provides a low‐level flux from autumn to spring in ice‐free streams. This flux varies with in‐stream productivity, and declines exponentially with distance from the stream edge. Some predators aggregate near streams and forage on these prey during periods of peak emergence, whereas others rely on the lower subsidy from autumn through spring when terrestrial prey are scarce. Several field experiments that manipulated this subsidy showed that it affected the short‐term behaviour, growth, and abundance of terrestrial consumers. 4. Reciprocal prey subsidies also have important indirect effects on both stream and riparian food webs. Theory predicts that allochthonous prey should increase density of subsidised predators, thereby increasing predation on in situ prey and causing a negative indirect effect via apparent competition. However, short‐term experiments have produced either positive or negative indirect effects. These contrasting results may be due to characteristics of the subsidies and individual consumers, but could also result from differences in experimental designs. 5. New study approaches are needed to better determine the direct and indirect effects of reciprocal prey subsidies. Experiments coupled with comparative research will be required to measure their effects on individual consumer fitness and population demographics. Future work should investigate whether reciprocal prey fluxes stabilise linked stream–riparian ecosystems, explore how landscape context affects the magnitude and importance of subsidies, and determine how impacts of human disturbance can propagate between streams and riparian zones via these trophic linkages. Study of these reciprocal connections is helping to define a more holistic perspective of catchments, and has the potential to shape new directions for ecology in general.     

Trade-offs between dispersal and competitive ability: a comparative study of wind-dispersed Asteraceae forbs

An underlying assumption in many models of coexistence and species response to fragmentation is the trade-off between dispersal and competitive abilities among species. Despite a well-founded theoretical ground for this assumption, the mechanism itself has not been as thoroughly explored. Empirical studies of the dispersal/competition trade-off have so far mainly concerned the dispersal distance of single offspring, whereas most models where the trade-off is assumed concern dispersal rate, i.e. the number of offspring that is dispersed outside a local patch per time unit. When species differ in fecundity this should also affect the dispersal rate. We therefore investigated different aspects of dispersal ability and competitive ability in the recruitment phase for 15 wind-dispersed Asteraceae species. A trade-off was found between dispersal ability at the offspring level, i.e. distance travelled by single seeds, and competitive ability in the recruitment phase, but no trade-off was found between dispersal ability at the brood level, i.e. the dispersal ability of single seeds in combination with fecundity, and competitive ability in the recruitment phase. The results were supported both by cross-species analysis and analyses by phylogenetically independent contrast. If this is a general pattern then it is troublesome for models making the assumption that there is a trade-off between dispersal rate and competitive ability.     

Warming alters the size spectrum and shifts the distribution of biomass in freshwater ecosystems

Organism size is one of the key determinants of community structure, and its relationship with abundance can describe how biomass is partitioned among the biota within an ecosystem. An outdoor freshwater mesocosm experiment was used to determine how warming of～4 °C would affect the size, biomass and taxonomic structure of planktonic communities. Warming increased the steepness of the community size spectrum by increasing the prevalence of small organisms, primarily within the phytoplankton assemblage and it also reduced the mean and maximum size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in changes in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganization of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure and functioning of aquatic communities and ecosystems.     

The use of habitat mosaics by terrestrial vertebrate fauna: implications for conservation and management

Many species of vertebrates require multiple habitats to obtain different resources at different stages of their life-cycles. Use of habitat mosaics takes place on a variety of spatial and temporal scales, from a daily requirement for adjacent habitats to seasonal use of geographically separated environments. Mosaics of habitats are also required in some species to allow ontogenetic habitat shifts, while in others each sex may have specific requirements that are met by different habitats. The extent and nature of animal movements are key (but generally poorly known) factors affecting the vulnerability of species to landscape change. The requirement by many species for multiple habitats suggests that their conservation will be most effective in a mosaic environment and that protection of certain high profile habitats alone, such as rainforest, will be insufficient to achieve conservation goals. Management regimes that result in homogenization of habitats should be avoided. Priority should be given to research that identifies the extent to which species can locate habitat mosaics, at different spatial scales and arrangements, in modified environments.     

Influence of soil fauna on fungal plant pathogens in agricultural and horticultural systems

An understanding of the ecology of plant pathogens is crucial for the development of agricultural and horticultural growing systems that enhance plant health. One important group of organisms that influences plant pathogen survival and dispersal is the soil fauna. This review deals with known and possible interactions between soil animals and different groups of fungal plant pathogens. It is suggested that facultative saprophytes may be affected considerably by mycelial grazing by soil animals, while obligate pathogens may be more influenced by animals that ingest spores and other types of propagules. Both types of pathogens can also be influenced by indirect interactions with the soil fauna. Manipulating the soil environment for enhancement of beneficial soil animals that consume pathogens seems to be a realistic possibility for sustainable agriculture and horticulture.     

Changes in trophic level of Squatina guggenheim with increasing body length: relationships with type, size and trophic level of its prey

The occurrence of changes in the trophic level (TL) of sharks with growth has not been quantified until now. Here length-related changes on Squatina guggenheim Marini trophic level were determined, and shifts in type, size and trophic level of its prey were analysed. Sampling took place during five bottom trawl surveys conducted in the Argentine–Uruguayan Common Fishing Zone during spring (December/1995, October/1997) and fall (March/1997, March–April/1998, May–June/1998), using an Engel bottom-trawl net to capture the sharks. Three length groups were defined based on diet composition and using a cluster analysis (group I, 23–60 cm; group II, 61–80 cm; group III, 81–91 cm L _T). An ANOSIM procedure detected significant differences (P < 0.05) in the diet spectrum between the three length groups. The smallest sharks (group I) ingested fish prey ranging from 5 to 21 cm L _T, medium sharks (group II) fed on fish prey between 11 and 35 cm L _T, and largest sharks (group III) preyed on fish between 13 and 40 cm L _T. Diet structure of length groups were discriminated by almost the same prey taxa that characterized them. The increase of S. guggenheim body length promoted a decrease in the relative importance of small pelagic fishes. Contrarily, prey as medium benthopelagic fishes, medium pelagic squid and medium benthopelagic fishes showed an inverse tendency, indicating a broad diet spectrum of adults. Predator-length and prey-length relationship indicated a trend where 44.8% of S. guggenheim diet was integrated by prey <20% of their own body length and 32.8% of their diet was composed by prey >30% of their own length. The increase of mean prey weight was associated with the increase of predator weight and length. Smallest sharks (group I) were identified as secondary consumers (TL < 4) whereas medium sharks (group II) and largest sharks (group III) were placed as tertiary consumers (TL > 4). The study revealed an increase in S. guggenheim TL with shark growth as a consequence of changes on type, size and TL of prey ingested.     

Measurement of body size and abundance in tests of macroecological and food web theory

1. Mean body mass (W) and mean numerical (N) or biomass (B) abundance are frequently used as variables to describe populations and species in macroecological and food web studies. 2. We investigate how the use of mean W and mean N or B, rather than other measures of W and/or accounting for the properties of all individuals, can affect the outcome of tests of macroecological and food web theory. 3. Theoretical and empirical analyses demonstrate that mean W, W at maximum biomass (W(mb)), W when energy requirements are greatest (W(me)) and the W when a species uses the greatest proportion of the energy available to all species in a W class (W(mpe)) are not consistently related. 4. For a population at equilibrium, relationships between mean W and W(me) depend on the slope b of the relationship between trophic level and W. For marine fishes, data show that b varies widely among species and thus mean W is an unreliable indicator of the role of a species in the food web. 5. Two different approaches, 'cross-species' and 'all individuals' have been used to estimate slopes of abundance-body mass relationships and to test the energetic equivalence hypothesis and related theory. The approaches, based on relationships between (1) log(10) mean W and log(10) mean N or B, and (2) log(10) W and log(10) N or B of all individuals binned into log(10) W classes (size spectra), give different slopes and confidence intervals with the same data. 6. Our results show that the 'all individuals' approach has the potential to provide more powerful tests of the energetic equivalence hypothesis and role of energy availability in determining slopes, but new theory and empirical analysis are needed to explain distributions of species relative abundance at W. 7. Biases introduced when working with mean W in macroecological and food web studies are greatest when species have indeterminate growth, when relationships between W and trophic level are strong and when the range of species'W is narrow.     

Integration of lakes and streams in a landscape perspective: the importance of material processing on spatial patterns and temporal coherence

1. We studied the spatial and temporal patterns of change in a suite of twenty‐one chemical and biological variables in a lake district in arctic Alaska, U.S.A. The study included fourteen stream sites and ten lake sites, nine of which were in a direct series of surface drainage. All twenty‐four sites were sampled between one and five times a year from 1991 to 1997. 2. Stream sites tended to have higher values of major anions and cations than the lake sites, while the lake sites had higher values of particulate carbon, nitrogen, phosphorous and chlorophyll a. There were consistent and statistically significant differences in concentrations of variables measured at the inlet versus the outlet of lakes, and in variables measured at upstream versus downstream sites in the stream reaches which connect the lakes. In‐lake processing tended to consume alkalinity, conductivity, H⁺, DIC, Ca²⁺, Mg²⁺, CO₂, CH₄, and NO₃^–, and produce K⁺ and dissolved organic carbon (DOC). In‐stream processing resulted in the opposite trends (e.g. consumption of K⁺ and DOC), and the magnitudes of change were often similar to those measured in the lakes but with the opposite sign. 3. Observed spatial patterns in the study lakes included mean concentrations of variables which increased, decreased or were constant along the lake chain from high to low altitude in the catchment (stream sites showed no spatial patterns with any variables). The strongest spatial patterns were of increasing conductivity, Ca²⁺, Mg²⁺, alkalinity, dissolved inorganic carbon and pH with lake chain number (high to low altitude in the basin). These patterns were partly determined by the effect of increasing catchment area feeding into lakes further downslope, and partly by the systematic processing of materials in lakes and in the stream segments between lakes. 4. Synchrony (the temporal coherence or correlation of response) of variables across all lakes ranged from 0.18 for particulate phosphorus to 0.90 for Mg²⁺ the average synchrony for all twenty‐one variables was 0.50. The synchronous behaviour of lake pairs was primarily related to the spatial location or proximity of the lakes for all variables taken together and for many individual variables, and secondarily, to the catchment to lake area ratio and the water residence time. 5. These results illustrate that, over small geographic areas, and somewhat independent of lake or stream morphometry, the consistent and directional (downslope) processing of materials helps produce spatial patterns which are coherent over time for many limnological variables. We combine concepts from stream, lake and landscape ecology, and develop a conceptual view of landscape mass balance. This view highlights that the integration of material processing in both lakes and rivers is critical for understanding the structure and function of surface waters, especially from a landscape perspective.     

Movement of two grassland butterflies in the same habitat network: the role of adult resources and size of the study area

Abstract. 1.  Movement patterns of two butterfly species (meadow brown Maniola jurtina L. and scarce copper Lycaenae virgaureae L.) were studied in a 172 ha area within a landscape with a high percentage of suitable habitats for mark–release–recapture experiments.
2.  Adult resource density, but not patch size or larval food plant abundance, influenced the numbers and the fractions of residents, emigrants, and immigrants.
3.  Differences between species were observed in movement frequency and maximum distances moved but not in mean distances moved.
4.  The scarce copper showed much greater movement ability than expected from the results of published studies. This is believed to be a result of the comparatively large size of the study area and the high cover of suitable habitat (>50%).
5.  The mean and maximum distances travelled by butterflies reflected differences in the size of the study area.     

Examining the Links between Biodiversity and Human Health: An Interdisciplinary Research Initiative at the U.S. Environmental Protection Agency

Under the U.S. Environmental Protection Agency’s mission to protect human health and the environment, the agency seeks to conduct research on the structure and function of ecosystems and to improve our understanding of the processes that contribute to the sustained health of the nation’s ecosystems and the well-being of human populations. Changes in biodiversity can profoundly impact the ability of ecosystems to provide clean water, energy, food, recreation, and other services that contribute to human well-being. In addition, changes in biodiversity can affect the transmission of infectious disease to humans, particularly vectorborne diseases such as malaria and Lyme disease. The Environmental Protection Agency’s new initiative supports interdisciplinary research to characterize the mechanisms that link biodiversity and human health and to use this knowledge to develop integrative tools and approaches for quantifying and predicting these relationships. Research on these links can have an important impact on our view of biodiversity and how we manage resources to protect human and ecosystem health. Disclaimer: This work was funded in part under Grant #CX3-832328 with the American Association for the Advance of Science (AAAS). The views expressed do not necessarily reflect the views of the Environmental Protection Agency.