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The purpose of this study was to identify the use of marine versus terrestrial food items by terrestrial arthropod predators on Baltic Sea shores. The inflow of marine nutrients in the area consists mainly of marine algal detritus and emerging aquatic insects (e.g., chironomids). Diets of coastal arthropods were examined using carbon and nitrogen stable isotope analysis in a two source mixing model. The results suggest that spiders are the terrestrial predators mainly utilizing nutrients and energy of marine origin on Baltic Sea shores, whereas insect predators such as beetles and heteropterans mainly utilize nutrients and energy derived from terrestrial sources, possibly owing to differences in hunting behaviour. That spiders are the predators which benefit the most from the marine inflow suggest that eventual effects of marine subsidies for the coastal ecosystem as a whole are likely mediated by spiders. L'objectif de notre etude est de determiner l'utilisation relative des sources alimentaires marines et terrestres par les arthropodes terrestres predateurs sur les cotes de la Baltique. L'apport de nutriments marins dans la region consiste en des debris d'algues marines et d'insectes aquatiques (par ex., des chironomides) qui emergent. Nous examinons les regimes alimentaires d'arthropodes cotiers a l'aide d'une analyse des isotopes stables de carbone et d'azote dans un modele de melange a deux sources. Nos resultats indiquent que les araignees sont des predateurs terrestres qui utilisent surtout des nutriments et de l'energie d'origine marine sur les cotes de la Baltique, alors que les insectes predateurs, tels que les coleopteres et les heteropteres, utilisent surtout des nutriments et de l'energie provenant des sources terrestres, peut-etre a cause de differences dans leurs comportements de chasse. Le fait que les araignees soient les predateurs qui beneficient le plus des apports marins indique que les effets eventuels des apports marins sur l'ecosysteme cotier dans son ensemble se font vraisemblablement par l'intermediaire des araignees. [Traduit par la Redaction], Introduction Many terrestrial predators are known to aggregate in large numbers along shorelines and by various water bodies around the world (Polis et al. 1997, 2004; Sanzone et al. 2003). [...]

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1600-0706.2009.17540.x Byline: Hannah Ostergard, Peter A. Hamback, Johan Ehrlen Abstract: Fluctuations of resources in time and space will influence not only species abundance but also interactions among species. For plant-consumer interactions, the effects of resource variation have mostly been studied in systems with high resource variability. Systems with moderate variations are less studied, although ecological and evolutionary dynamics of plants and consumers are likely to be affected also by less extreme variability. The effects of variation in a particular resource should depend on consumer diet width. We examined how spatial and temporal variation in seed production in the perennial herb Lathyrus vernus influenced population dynamics and resource utilization in two beetle pre-dispersal seed predators with different host ranges over six years. The monophagous Apion opeticum occupied fewer patches and had lower densities than the oligophagous Bruchus atomarius. The proportion of seeds attacked increased with increases in seed production between years for both seed predators. A possible explanation for these patterns is that population dynamics of beetles are driven largely by local factors and that the same factors influence both beetle performance and seed production. In B. atomarius, patterns may also be influenced by a more pronounced preference for L. vernus in years with a high seed production in L. vernus. We conclude that relatively modest variation in seed production may result in responses that differ in both direction and extent from those usually observed in systems with high variation in seed production. Article History: Manuscript Accepted 3 April 2009 Article note: H. Ostergard, P. A. Hamback and J. Ehrlen (ehrlen@botan.su.se), Dept of Botany, Stockholm Univ., Lilla Frescativ. 5, SE-106 91 Stockholm, Sweden.

To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1600-0706.2009.17177.x Byline: Peter A. Hamback, James Gilbert, Katie Schneider, Holly M. Martinson, Gundula Kolb, William F. Fagan Abstract: Ecological stoichiometry has emerged as a tool for exploring nutrient demand and evolutionary responses to nutrient limitation. Previous studies of insects have found predictable variability in stoichiometry, both in relation to body size and trophic mode, at ordinal levels or higher. Our study further examines the evolutionary and ecological lability in these traits by comparing the effects of body size, trophic mode (larval and adult) and larval habitat on the stoichiometry of insects within one order (Diptera). The study also expands on previous work by analyzing trophic mode both at coarse (detritivore, herbivore, predator) and fine (high- vs low- nutrient quality resources within trophic categories) scales and by comparing nutrient stoichiometry in two geographical regions, Sweden and Arizona. As predicted, adults feeding on nectar or pollen had the lowest body N content in the dataset. Additionally, for Diptera with predatory larvae, species low N diets had lower body N content than those with high N diets. However, body N content was not consistently lower for all species with low N resources, as species feeding on plant material were indistinguishable in stoichiometry from predators with high N diets. We suggest that these results emerge because larval resource exploitation is poorly understood in herbivorous Diptera species. Body P content for Swedish Diptera decreased with body size for all trophic modes, and the only difference among trophic modes was that blood feeders had higher P content than other groups. The regional comparison further showed that the allometry of body P content is a labile trait that may vary at regional scales, as there was no allometric scaling of body P content in the Arizona data set, in contrast to the Swedish data set. These results are not easily explained by existing theoretical frameworks, but instead point to a general context-dependence of P stoichiometry, which should now be a focus for future work. Article History: Manuscript Accepted 29 October 2008 Article note: P. A. Hamback (peter.hamback@botan.su.se) and G. Kolb, Dept of Botany, Stockholm Univ., SE-106 91 Stockholm, Sweden. - J. Gilbert, K. Schneider, H. M. Martinson and W. F. Fagan, Dept of Biology, Univ. of Maryland, College Park, MD 20742, USA.

Inter- and intraspecies variations in host plant traits are presumably involved in many host shifts by insect herbivores, and elucidating the mechanisms involved in such shifts has been a crucial goal in insect-plant research for several decades. Here we propose that herbivore-induced evolutionary increases in host plant resistance may cause oligophagous insect herbivores to shift to other sympatric plants as currently preferred host plants become increasingly unpalatable. We tested this hypothesis in a system based on the perennial herb Filipendula ulmaria (Rosaceae), whose herbivory defense has become gradually stronger due to prolonged selection by Galerucella tenella (Coleoptera: Chrysomelidae) herbivory in a boreal archipelago. We show that Galerucella gradually increases its use of the alternative host plant Rubus arcticus (Rosaceae) in parallel to gradually increased resistance in Filipendula. Our results imply that, by driving the evolutionary increase in Filipendula resistance, Galerucella is also gradually making the original host species more unpalatable and thereby driving its own host-breadth enlargement. We argue that such self-inflicted 'rent rises' may be an important mechanism behind host plant shifts, which in turn are believed to have preceded the speciation of many phytophagous insects. Key words: coevolution; Filipendula ulmaria; Galerucella tenella; herbivore; host shift; resistance; Rubus arcticus; Skeppsvik Archipelago, Sweden.

Oviposition sites of phytophagous insects should correlate with plant traits that maximize survival of the progeny. Plants, on the other hand, should benefit from traits and developmental patterns that complicate oviposition decisions. In the antagonistic interaction between plant and pre-dispersal seed predator the time lag between egg laying and seed development may allow for abortion of fruits in plants, potentially reducing fitness loss through predation. We studied the perennial herb Lathyrus vernus and the beetle pre-dispersal seed predator Bruchus atomarius in Sweden to determine the fitness consequences of nonrandom fruit abortion in the plant and oviposition patterns of the beetle. The beetle had a sophisticated ability to locate fruits with high probability of retention, partly by fruit position and phenology but also by some additional unidentified cue. Mortality of eggs was density dependent, but still the egg-laying pattern was clumped. We found no defensive strategy in the plant; instead the predictable fruit abortion pattern was associated with decreased plant fitness. We discuss how interactions may pose simultaneous selection pressures on plant and insect traits and how life history traits and other selective forces may shape the adaptive outcome of the interaction in plant and insect, respectively. Key words: Bruchus atomarius; fruit abortion; herbivore offense; Lathyrus vernus; oviposition; plantanimal interactions; plant defense.

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.2007.0030-1299.15800.x Byline: Peter A. Hamback, Majbritt Vogt, Teja Tscharntke, Carsten Thies, Goran Englund Abstract: The relationship between density and area depends on local growth rates and the area-dependence of migration rates. These rates vary among taxa due to dispersal behaviour, plot productivity and natural enemy impact. Previous studies in aphids suggest that aphid densities are highest in patches of intermediate sizes, and lower in small and large patches. The suggested mechanism causing these patterns is that the dispersal behaviour in aphids creates a mixture of area- and perimeter-dependent migration rates. In this paper, we used these predictions to examine the additional consequences of nutrient availability and natural enemies on the density-area relationship. The derived predictions were compared to data from a system with three aphid species, a set of aphid parasitoids and generalist natural enemies, and at two levels of plant nutrient availability. We find that predictions from the model based only on dispersal and local growth agree with the temporal dynamics of density-area relationships for aphids in high nutrient patches. In patches with low nutrients, high parasitism rates appeared to cause a negative density-area relationship for aphids, thereby deviating from predictions driven by the aphids' dispersal behavior. Hence, the dispersal model with scale-dependent migration rates can provide a useful tool for understanding insect distribution in patch size gradients, but the relative importance of top-down effects can completely change with plot productivity. Article History: Manuscript Accepted 16 July 2007 Article note: P. A. Hamback (peter.hamback@botan.su.se), Dept of Botany, Stockholm Univ., SE-106 91 Stockholm, Sweden. - M. Vogt, T. Tscharntke and C. Thies, Agroecology, Univ. of Gottingen, Waldweg 26, DE-370 73 Gottingen, Germany. - G. Englund, Dept of Ecology and Environmental Science, Umea Univ., SE-901 87 Umea, Sweden.

Habitat fragmentation may strongly affect species density, species interactions, and the rate of ecosystem processes. It is therefore important to understand the observed variability among species responses to fragmentation and the underlying mechanisms. In this study, we compare density--area relationships (DARs) for 344 lepidopteran species belonging to 22 families (butterflies and moths). This analysis suggested that the [DAR.sub.slope] is generally positive for moths and negative for butterflies. The differences are suggested to occur because moths are largely olfactory searchers, whereas most butterflies are visual searchers. The analysis also suggests that DARs vary as a function of habitat specialization and body size. In butterflies, generalist species had a more negative [DAR.sub.slope] than specialist species because of a lower patch size threshold. In moths, the differences in [DAR.sub.slope] between forest and open habitat species were large for small species but absent for large species. This difference is argued to occur because the DARslope in large species mainly reflects their search mode, which does not necessarily vary between moth groups, whereas the slope in small species reflects population growth rates. butterflies and moths | habitat fragmentation | Lepidoptera | life history traits | olfactory and visual information

Vole densities, plant damage and plant cover were examined in areas with or without small mammal predators to examine the potential of trophic cascades in a shrubby tundra ecosystem. Three out of five dwarf shrub species was substantially reduced on predator-free islands, providing evidence for strong cascading effects in a rather large-scale terrestrial system.

In this paper, we examine how per capita emigration rates vary with patch size. Analyses of analytic diffusion models and lattice simulations show that the scale dependence of emigration rates is expected to differ between small and large patches. In large patches, per capita emigration rate (E) is given by E = k[A.sup.-[beta]]. A is the area, k is a constant, and [beta], which describes the strength of the scale dependence, is given by [beta] = 1 -d/2, where d is the fractal dimension of the patch boundary. In small patches, the scale dependence is predicted to level off, and the value of the scaling coefficient ([beta]) is influenced by details about how movement behaviors and mortality rates vary across patch boundaries. However, much of this variation can be explained as effects on the magnitude of per capita emigration rates. Analyses of published empirical studies of the scale dependence of emigration in terrestrial insects show that observed scaling coefficients are within the expected range (0 < [beta] < 0.5), and that scaling coefficients decrease with decreasing scale. Moreover, we find that the fractal dimension of patch boundaries and the magnitude of emigration explain much of the observed variation between different patch networks, species, years, and sexes. Key words: emigration; extinction risk; insects; meta-analysis; metapopulation models; patch networks; patch size; scale dependence.

To evaluate the role of natural enemies for the coexistence of competing species, it is necessary to estimate quantitatively the way in which the selectivity of the natural enemies changes the strength of competition between the competitors. This paper presents one method for doing this in host-parasitoid systems with discrete generations. The method is illustrated by analyzing the interaction between variegated leafhoppers (Erythroneura variabilis) and grape leafhoppers (E. elegantula) feeding on domestic grapes. The analysis confirms earlier observations that the recent replacement of grape leafhoppers with variegated leafhoppers is likely to be a consequence of the shared egg parasitoid Anagrus epos. Finally, we argue that the method can provide a tool to evaluate the potential of biological control measures involving alternative prey, e.g., in intercropping systems. Key words: Anagrus epos; apparent competition; biological control; competitive displacement; Erythroneura; host-parasitoid model; leafhoppers.

A spatially explicit model is presented for assessing the degree of overharvesting among 12 game species in Ecuador. Findings are presented, and the role of the model in determining no-take areas and the development of sustainable hunting policies is discussed.

The study of the scale-dependence of migration rates in stream invertebrates is conducted with the use of analytical models and random walk simulations in a one-dimensional habitat. Results reveal that the models and the published data on drift distances can be used to effectively calculate the expected scale-dependence of per capita emigration rates, under a wide range of environmental conditions.

The prevalence and potential for interactive effects between herbivory and competition on plant growth and biomass is discussed. The mismatch between the spatial scale of herbivore behavior and the spatial heterogeneity of the plant community that give rise to interactive effects is examined.