Experimentally broken faecal sacs affect nest bacterial environment,development and survival of spotless starling nestlings

Nestlings of most avian species produce faecal sacs, which facilitate the removal of nestlings’ excrements by parents, thereby reducing proliferation of potentially pathogenic microorganisms and/or detectability by predators and parasites. The nest microbial environment that birds experience during early life might also affect their development and thus, faecal sacs facilitating parental removal may be a strategy to decrease bacterial contamination of nests that could harm developing nestlings. Here, we tested this hypothesis by experimentally broken faecal sacs and spreading them in nests of spotless starlings Sturnus unicolor, thereby avoiding their removal by adults. In accordance with the hypothesis, experimental nests harboured higher bacterial density than control nests. Nestlings in experimental nests were of smaller size (tarsus length) and experienced lower probability of survival (predation) than those in control nests. Moreover, nestlings in experimental nests tended to suffer more from ectoparasites than those in control nests. We discuss the possible pivotal role of bacteria producing chemical volatiles that ectoparasites and predators might use to find avian nests, and that could explain our experimental results in starlings.     

Impacts of sea star predation on mussel bed restoration

Predation by sea stars has the potential to cause elevated levels of mortality in reestablished populations of bivalves relative to levels of recruitment. Recent efforts to restore beds of the nearly extirpated green‐lipped mussel within the Hauraki Gulf, New Zealand, resulted in high abundances of sea stars occupying those beds and it is unknown whether predation poses a potential limitation to the success of restoration in this bivalve species. The contribution of predation by sea stars to the mortality of mussels across four experimental mussel beds over a 2‐year period was estimated using data from regular assessments of sea star abundance and an experimentally determined consumption rate of sea stars upon mussels. In addition, the potential size selection of mussels by sea stars was assessed to determine if large sea stars selected for recent settlers. Sea stars' abundance within the mussel beds grew to an average of 0.57 sea stars/m² within 9 months, remaining at similar levels throughout the study. These predominantly large sea stars were estimated to have consumed 30.1% of the mussels over a 25‐month period, representing a contribution of 40.4% of the mussel mortality. Sea stars predominantly selected for larger mussels, and their predation likely contributes little to any lack in mussel recruitment. Sea star predation is clearly a limiting factor on the survival of transplanted adult mussels and the present study highlights the need to continually assess predation risk to determine if remediation is necessary for the persistence of the restored beds.     

Disruption of the vasopressin 1b receptor gene impairs the attack component of aggressive behavior in mice

Vasopressin affects behavior via its two brain receptors, the vasopressin 1a and vasopressin 1b receptors (Avpr1b). Recent work from our laboratory has shown that disruption of the Avpr1b gene reduces intermale aggression and reduces social motivation. Here, we further characterized the aggressive phenotype in Avpr1b -/- (knockout) mice. We tested maternal aggression and predatory behavior. We also analyzed the extent to which food deprivation and competition over food increases intermale aggression. We quantified defensive behavior in Avpr1b -/- mice and later tested offensive aggression in these same mice. Our results show that attack behavior toward a conspecific is consistently reduced in Avpr1b -/- mice. Predatory behavior is normal, suggesting that the deficit is not because of a global inability to detect and attack stimuli. Food deprivation, competition for food and previous experience increase aggression in both Avpr1b +/+ and -/- mice. However, in these circumstances, the level of aggression seen in knockout mice is still less than that observed in wild-type mice. Defensive avoidance behaviors, such as boxing and fleeing, are largely intact in knockout mice. Avpr1b -/- mice do not display as many 'retaliatory' attacks as the Avpr1b +/+ mice. Interestingly, when territorial aggression was measured following the defensive behavior testing, Avpr1b -/- mice typically show less initial aggressive behavior than wild-type mice, but do show a significant increase in aggression with repeated testing. These studies confirm that deficits in aggression in Avpr1b -/- mice are limited to aggressive behavior involving the attack of a conspecific. We hypothesize that Avpr1b plays an important role in the central processing that couples the detection and perception of social cues (which appears normal) with the appropriate behavioral response.     

Functional response of early stages of the cuttlefish Sepia officinalis preying on the mysid Mesopodopsis slabberi

The functional response of Sepia officinalis early stages, preying on mysids of the species Mesopodopsis slabberi was investigated. The effects of five prey densities (12.5, 25, 37.5, 50 and 125 mysids l^-1) and two hatchling ages (1-day-old and 7-day-old) on consumption rate and the frequency of non-feeding animals were tested. Older animals were approximately 50% heavier than newly hatched ones. Hatchlings were individually assayed under 0.25 W m^-2 natural light, 37.8 psu in salinity and 19°C. The effect of prey density on consumption rate was highly significant and no effect of age was detected within the age range tested. Maximal values recorded for consumption rate were about 0.45 mysids h^-1. The frequency of non-feeding individuals was strongly reduced at saturating prey densities. The functional response curve showed an interval of prey densities for which density-dependent prey mortality is probable.     

Interference competition among native and invader amphipods

Aquarium experiments were used to study indications of interference competition, such as substratum choice shifts, swimming activities and mortality of invasive and indigenous gammarids in each other's presence. The more recent invaders Gammarus tigrinus and Dikerogammarus villosus were more likely to prefer stone substratum, whereas the native Gammarus pulex and an earlier invader Gammarus roeseli were found more frequently in the water layer. Sand was the least likely substratum to be chosen by any of the species. G. pulex and G. roeseli did not alter their substratum preference in each other's presence. In the presence of D. villosus, G. pulex shifted towards smaller stones and increased its swimming activities, whereas D. villosus did not change its behaviour in the presence of G. pulex. These shifts may indicate interference competition, with D. villosus being the stronger competitor. The greatest shifts in substratum preference arose when one species had occupied a substratum before the other one was introduced, especially when D. villosus was already present before G. pulex was introduced, possibly indicating pre-emptive competition. Swimming activities of G. pulex increased in the presence of D. villosus, whereas D. villosus spent little time swimming. Mortality was comparable between the different experiments without any indication of predation. The effect of Intra Guild Predation (IGP) may not be reflected adequately by short-time experiments as moults occurred seldom during the experiments. Although no IGP was observed during our experiments, habitat shifts occurred, which may indicate that competitive interactions are apparent before IGP starts. Such shifts may serve to avoid intraguild competition.     

Diel vertical migration of the copepod <Emphasis Type="Italic">Thermocyclops inversus</Emphasis> (Kiefer, 1936) in a tropical reservoir: the role of oxygen and the spatial overlap with <Emphasis Type="Italic">Chaoborus</Emphasis>

The effect of water transparency, dissolved oxygen concentration and the invertebrate predator Chaoborus brasiliensis on the day–night vertical distribution of the copepod cyclopoid Thermocyclops inversus was investigated in a shallow tropical reservoir, Nado Reservoir, Belo Horizonte, Brazil. Diel cycles were carried out over a period of 12 consecutive months, between October 1999 and September 2000. The different developmental stages of T. inversus exhibited diel vertical migration (DVM) and displayed a clear ontogenetic trend, with the amplitude of DVM increasing with the age of the organism, and ranging from 0.4 m to 0.8 m for nauplii, 0.4 m to 1.2 m for copepodite, and 1.1 m to 2.1 m for adults. We observed that seasonal changes in dissolved oxygen and C. brasiliensis directly influenced the vertical distribution of the copepod population in this reservoir. Furthermore, it was showed that the diurnal vertical migration is an important predator avoidance behavior since it diminished the spatial overlap between prey and its potential predator. This finding supports the hypothesis that the vertical migration is a defense mechanism against predation. Thus, T. inversus is able to remain in the anoxic layers during day light hours, and at night they move upwards avoiding hypolimnetic waters to escape from predation by Chaoborus.     

Human-induced Trophic Cascades and Ecological Regime Shifts in the Baltic Sea

Abstract The ecosystems of coastal and enclosed seas are under increasing anthropogenic pressure worldwide, with Chesapeake Bay, the Gulf of Mexico and the Black and Baltic Seas as well known examples. We use an ecosystem model (Ecopath with Ecosim, EwE) to show that reduced top-down control (seal predation) and increased bottom-up forcing (eutrophication) can largely explain the historical dynamics of the main fish stocks (cod, herring and sprat) in the Baltic Sea between 1900 and 1980. Based on these results and the historical fish stock development we identify two major ecological transitions. A shift from seal to cod domination was caused by a virtual elimination of marine mammals followed by a shift from an oligotrophic to a eutrophic state. A third shift from cod to clupeid domination in the late 1980s has previously been explained by overfishing of cod and climatic changes. We propose that the shift from an oligotrophic to a eutrophic state represents a true regime shift with a stabilizing mechanism for a hysteresis phenomenon. There are also mechanisms that could stabilize the shift from a cod to clupeid dominated ecosystem, but there are no indications that the ecosystem has been pushed that far yet. We argue that the shifts in the Baltic Sea are a consequence of human impacts, although variations in climate may have influenced their timing, magnitude and persistence. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Size and taxonomic constraints determine the seed preferences of Carabidae (Coleoptera)

Several species of carabid beetles are important postdispersal predators of the seeds of herbaceous plants. The preferences of carabids for particular seeds differ, but the factors that determine their choice are little studied. We tested the hypothesis that preferences are determined by taxonomic constraints (carabid species affiliation), and carabid and seed size. The preferences were determined for adults of 30 species of central European field carabids mainly belonging to the tribes Zabrini (17 species) and Harpalini (10 species) (body mass 1–36 mg). In a cafeteria experiment the beetles were offered an excess of seeds from 28 species of dicotyledoneous herbaceous plants (mass 0.1–8.7 mg). The number of seeds eaten during a 5-day experiment was used as an estimate of preference. Mass of the preferred species of seed eaten was positively related to carabid body mass in both tribes. Multivariate analysis indicated three groups of carabid species with marked preferences for particular species of seeds: (i) species of Harpalini favoured mainly the seed of Cirsium arvense and Viola arvensis, (ii) some species of Zabrini the seeds of Asteraceae (Taraxacum officinale, Tripleurospermum inodorum and Crepis biennis) and (iii) other species of Zabrini the small seeds of Brassicaceae and Caryophyllaceae. The species of Harpalini were more generalist and accepted a greater proportion of seed species than Zabrini of the same size. Preferences of carabid seed predators were thus determined by taxonomic and size constraints, as in other groups of predators.     

Seed transfer among bird-dispersed trees and its consequences for post-dispersal seed fate

We investigated seed transfer, i.e. the seed movement away from a source canopy to areas beneath heterospecific canopies, among the ornithochorous tree species Taxus baccata, Ilex aquifolium and Crataegus monogyna in temperate secondary forests in NW Spain, by analysing the composition of multispecific seed rain beneath the canopy of each species, at four sites and for 2 years. To evaluate the consequences on seed fate, we estimated predation by rodents in manipulated seed rains, representing variable levels of relative proportion and total density for combinations of a preferred species paired with a less-preferred species. Seed rain under Taxus canopies was dominated by Taxus seeds, which occurred in low proportion under heterospecific canopies. Ilex seeds dominated the areas under Ilex but accounted for 20–40% of seeds under heterospecific trees. Crataegus seeds were not dominant in any of the microhabitats. The probability of being deposited beneath a heterospecific canopy was much higher for Ilex and Crataegus than for Taxus. The effects of seed rain composition on post-dispersal seed predation were species-specific. Taxus seeds experienced lower predation when occurring in a background of seeds dominated by heterospecific, Ilex or Crataegus, seeds. Crataegus seeds escaped predation more successfully in high-density patches, independently of seed clump composition. Predation on Ilex seeds was independent to both the density and the composition of seed clump. Seed transfer among heterospecific tree species may contribute to shape the template of propagule abundances from which forest will develop, by generating seed combinations favourable to escape from predation.