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opencc-zeroApr 2020View details →

Data from: State-dependent decision-making by predators and its consequences for mimicry

The mimicry of one species by another provides one of the most celebrated examples of evolution by natural selection. Edible Batesian mimics deceive predators into believing they may be defended, whereas defended Müllerian mimics have evolved a shared warning signal, more rapidly educating predators to avoid them. However, it may benefit hungry predators to attack defended prey, while the benefits of learning about unfamiliar prey depends on the future value of this information. Previous energetic state-dependent models of predator foraging behaviour have assumed complete knowledge, while informational state-dependent models have assumed fixed levels of hunger. Here, we identify the optimal decision rules of predators accounting for both energetic and informational states. We show that the nature of mimicry is qualitatively and quantitatively affected by both sources of state dependence. Associative learning weakens the extent of parasitic mimicry by edible prey because naive predators often attack defended models. More importantly, mimicry among equally highly defended prey may be parasitic or mutualistic depending on the ecological context. Finally, mimicry by prey with intermediate defences corresponds to Batesian or Müllerian mimicry depending on whether the mimic is profitable to attack by hungry predators, but it is not a special case of mimicry.

opencc-zeroDec 2008View details →

Data from: Speciation has a spatial scale that depends on levels of gene flow

Area is generally assumed to affect speciation rates, but work on the spatial context of speciation has focused mostly on patterns of range overlap between emerging species rather than on questions of geographical scale. A variety of geographical theories of speciation predict that the probability of speciation occurring within a given region should (1) increase with the size of the region and (2) increase as the spatial extent of intraspecific gene flow becomes smaller. Using a survey of speciation events on isolated oceanic islands for a broad range of taxa, we find evidence for both predictions. The probability of in situ speciation scales with island area in bats, carnivorous mammals, birds, flowering plants, lizards, butterflies and moths, and snails. Ferns are an exception to these findings, but they exhibit high frequencies of polyploid and hybrid speciation, which are expected to be scale independent. Furthermore, the minimum island size for speciation correlates across groups with the strength of intraspecific gene flow, as is estimated from a meta‐analysis of published population genetic studies. These results indicate a general geographical model of speciation rates that are dependent on both area and gene flow. The spatial scale of population divergence is an important but neglected determinant of broad‐scale diversity patterns.

Data from: Temperature-dependent oxygen limitation and the rise of Bergmann's Rule in species with aquatic respiration

Bergmann's Rule is the propensity for species-mean body size to decrease with increasing temperature. Temperature-dependent oxygen limitation has been hypothesized to help drive temperature–size relationships among ectotherms, including Bergmann's Rule, where organisms reduce body size under warm oxygen-limited conditions, thereby maintaining aerobic scope. Temperature-dependent oxygen limitation should be most pronounced among aquatic ectotherms that cannot breathe aerially, as oxygen solubility in water decreases with increasing temperature. We use phylogenetically-explicit analyses to show that species-mean adult size of aquatic salamanders with branchial or cutaneous oxygen uptake becomes small in warm environments and large in cool environments, whereas body size of aquatic species with lungs (i.e., that respire aerially), as well as size of semi aquatic and terrestrial species do not decrease with temperature. We argue that oxygen limitation drives the evolution of small size in warm aquatic environments for species with aquatic respiration. More broadly, the stronger decline in size with temperature observed in aquatic vs terrestrial salamander species mirrors the relatively strong plastic declines in size observed previously among aquatic vs terrestrial invertebrates, suggesting that temperature-dependent oxygen availability can help drive patterns of plasticity, micro- and macroevolution.

Data from: Contrasting patterns of phenotype-dependent parasitism within and among populations of threespine stickleback

Variation in infection rate arises from variation in host exposure and resistance to parasites both within and among populations. All things being equal, phenotypes that increase exposure risk should covary positively with infection among individuals. It might therefore be expected that populations with mean phenotypes that increase exposure might also have higher rates of infection. However, such positive covariance between exposure and infection at the population level might be undermined by other factors such as geographic variation in parasite abundance or host resistance, negating or reversing in between-population comparisons. We studied rates of infection of two parasites among 18 populations of threespine stickleback (Gasterosteus aculeatus). As predicted, within populations, trophic morphology covaries with infection of two trophically transmitted parasites: individuals with benthic (or limnetic) phenotypes were more likely to be infected with a benthic (or limnetic) parasite. However, across populations, the relationship between morphology and infection rate was absent (limnetic parasite) or reversed (benthic parasite). Our results confirm the importance of phenotype-dependent exposure, but stress different factors or processes, such as the evolution of reduced susceptibility, might shape variation in infection at larger spatial scales.

Data from: Loss of heterosis and family-dependent inbreeding depression in plant performance and resistance against multiple herbivores under drought stress

1. Inbreeding depression (ID), outbreeding depression (OD) and heterosis can occur concurrently in plant populations. ID often increases under environmental stress, but the combined effects of inbreeding, outbreeding between populations and environmental stress, such as drought, on plant performance and herbivore resistance remain unclear. 2. In order to determine environment-dependent and family-dependent ID, OD and heterosis we conducted a common garden experiment with plants from five populations of Brassica nigra. Inbred, within-population outbred and between-population outbred plant families were exposed to drought or ambient water levels. We recorded the abundance and damage caused by specialist herbivores from contrasting feeding guilds, i.e. the phloem-feeding Brevicoryne brassicae, the leaf-chewing Psylliodes chrysocephalus and the stem-boring Ceutorhynchus quadridens larvae. 3. Drought stress had negative effects on growth, herbivore resistance and resistance against B. brassicae and positive effects on investments in reproductive output and plant secondary metabolites (sinigrin). We found drought stress-induced loss of heterosis for plant height and investment in reproductive output. Between-population outbred plants were more sensitive to drought stress in terms of above-ground biomass compared to within-population outbred plants. 4. Drought and inbreeding synergistically negatively influenced traits related to growth and reproductive output (environment-dependent inbreeding depression, EDID). There was high variation among families within populations in the degree of ID and EDID. Genetic variation in EDID could buffer the negative effects of genetic stress associated with habitat fragmentation and concurrent environmental stress. In order to capture fully the effects of both inbreeding and between-population outbreeding under stress the different spatial scales of the effects of inbreeding and between-population outbreeding should be taken into account. 5. Synthesis. Our results indicate that drought stress influences not only inbreeding depression (ID), but also heterosis. These findings shed new light on the combined effects of anthropogenic environmental change and the genetic consequences of habitat fragmentation on plants and their interactions with other organisms. Conservation programmes aiming to restore genetically degraded populations with the translocation of individuals between populations should consider environmental stress as a risk factor.

opencc-zeroDec 2016View details →

Data from: Tree-to-tree competition in mixed European beech-Scots pine forests has different impacts on growth and water-use efficiency depending on site conditions

1. Mixed conifer-hardwood forests can be more productive than pure forests and they are increasingly considered as ecosystems that could provide adaptation strategies in the face of global change. However, the combined effects of tree-to-tree competition, rising atmospheric CO2 concentrations and climate on such mixtures remain poorly characterized and understood. 2. To fill this research gap, we reconstructed 34-year series (1980-2013) of growth (basal area increment, BAI) and intrinsic water-use efficiency (iWUE) of Scots pine (Pinus sylvestris L.) – European beech (Fagus sylvatica L.) mixed stands at two climatically contrasting sites located in the southwestern Pyrenees. We also gathered data on tree-to-tree competition and climate variables in order to test the hypotheses that (i) radial growth will be greater when inter-specific competition exceeds intra-specific competition, i.e. when species complementarity occurs, and (ii) enhanced iWUE could be linked to improved stem radial growth. 3. Growth of both species was reduced when intra-specific competition increased. Species complementarity was linked to improved growth of Scots pine at the continental site, whilst competition overrode any complementarity advantage at the drought-prone Mediterranean site. Beech growth did not show any significant response to pine admixture likely due to shade tolerance and the highly competitive nature of this species. Increasing inter-specific competition drove recent iWUE changes, which increased in Scots pine but decreased in European beech. The iWUE enhancement did not involve any growth improvement in Scots pine. However, the positive BAI-iWUE relationship found for beech suggests an enhanced beech growth in drought-prone sites due to improved water use. 4. Synthesis. Complementarity may enhance growth in mixed forests. However, water scarcity can constrict light-related complementarity for shade intolerant species (Scots pine) in drought-prone sites. BAI-iWUE relationships were negative for Scots pine and positive for European beech. These contrasting behaviours have got implications for coping with the expected increasing drought events in Scots pine-European beech mixtures located near the ecological limit of the two species. Complementarity effects between tree species should be considered to avoid overestimating the degree of future carbon uptake by mixed conifer-broadleaf forests.

opencc-zeroDec 2011View details →

Data from: Density dependence and population regulation in marine fish: a large-scale, long-term field manipulation

Do small-scale experiments showing spatial density dependence in marine fishes scale-up to temporal density dependence and regulation of relatively large local populations? If so, what are the causative mechanisms and their implications? We conducted an 8-year multi-generation study of population dynamics of bicolor damselfish (Stegastes partitus) inhabiting four large coral reefs in the Bahamas. After a 4-year baseline period, it was clear that two populations naturally received very few settlement-stage larvae, so recruitment of recently settled fish was artificially enhanced at one low-settlement reef and reduced at one high-settlement reef to ensure a broad range of population sizes over which to test for regulation. Over all 8 years, populations on the two naturally high-settlement reefs experienced temporal density dependence in multiple per capita demographic rates mortality, survival to adulthood, and fecundity. These local populations also displayed components of regulation persistence, boundedness, and return tendency. Reefs supporting regulated populations were structurally complex, providing sufficient prey refuges that ensured high survival at low densities. In contrast, populations at low-settlement reefs experienced either density-independent or slightly inversely density-dependent demographic rates, even though recruitment was artificially augmented to high levels at one reef. There was no evidence of regulation at these reefs, and indeed, one local population suffered temporary extirpation. Here, habitat complexity was relatively low, increasing the risk of predation, especially at low population densities when fish would have to travel longer distances when finding mates or home sites inhabited by conspecifics. Among all demographic parameters, density dependence in individual growth (an indicator of within-species competition for food) was least correlated with the presence or absence of local population regulation. We conclude that, for systems like these, the environmental context of a local population -- especially predation risk and the distribution and abundance of spatial refuges -- is more important than the magnitude of larval supply alone in determining the existence of regulating density dependence. At the broader metapopulation scale, density dependence in both survival and fecundity exogenously caused by predation may provide regulation for the entire stock, even when endogenous within-species competition (assumed to be important in most fisheries models) is weak.

Data from: The magnitude of local adaptation under genotype-dependent dispersal

Dispersal moves individuals from patches where their immediate ancestors were successful to sites where their genotypes are untested. As a result, dispersal generally reduces fitness, a phenomenon known as "migration load." The strength of migration load depends on the pattern of dispersal and can be dramatically lessened or reversed when individuals move preferentially toward patches conferring higher fitness. Evolutionary ecologists have long modeled nonrandom dispersal, focusing primarily on its effects on population density over space, the maintenance of genetic variation, and reproductive isolation. Here, we build upon previous work by calculating how the extent of local adaptation and the migration load are affected when individuals differ in their dispersal rate in a genotype-dependent manner that alters their match to their environment. Examining a one-locus, two-patch model, we show that local adaptation occurs through a combination of natural selection and adaptive dispersal. For a substantial portion of parameter space, adaptive dispersal can be the predominant force generating local adaptation. Furthermore, genetic load may be largely averted with adaptive dispersal whenever individuals move before selective deaths occur. Thus, to understand the mechanisms driving local adaptation, biologists must account for the extent and nature of nonrandom, genotype-dependent dispersal, and the potential for adaptation via spatial sorting of genotypes.

opencc-zeroDec 2015View details →

Data from: Stay tuned: active amplification tunes tree-cricket ears to track temperature-dependent song frequency

Tree cricket males produce tonal songs, used for mate attraction and male–male interactions. Active mechanics tunes hearing to conspecific song frequency. However, tree cricket song frequency increases with temperature, presenting a problem for tuned listeners. We show that the actively amplified frequency increases with temperature, thus shifting mechanical and neuronal auditory tuning to maintain a match with conspecific song frequency. Active auditory processes are known from several taxa, but their adaptive function has rarely been demonstrated. We show that tree crickets harness active processes to ensure that auditory tuning remains matched to conspecific song frequency, despite changing environmental conditions and signal characteristics. Adaptive tuning allows tree crickets to selectively detect potential mates or rivals over large distances and is likely to bestow a strong selective advantage by reducing mate-finding effort and facilitating intermale interactions.

opencc-zeroDec 2014View details →

Data from: Interpopulation variation in a condition-dependent signal: predation regime affects signal intensity and reliability

In many models of sexual selection, conspicuous ornaments are preferred by mates because they indicate heritable signaler viability. To function as indicators, ornaments must exhibit a proportional relationship between expression and viability. In cases where the evolutionary interests of signaler and receiver diverge, selection favors exploitative exaggeration by low-viability individuals producing unreliable signals. Theory suggests that the evolutionary stability of such communication systems requires costs that prevent low-viability males from expressing disproportionately intense signals. Therefore, given ecological variation in signaling cost, the reliability of signaling systems will vary concomitantly. In this study, we assess the effect of a variable signal cost, predation, on signal intensity and reliability among 16 populations of Bahamas mosquitofish (Gambusia hubbsi) that use colorful dorsal fins in courtship displays. We found that fin coloration was more intense in low-predation sites and could be used to predict body condition. However, this predictive relationship was apparent only in populations subject to predation risk. We demonstrate an important role for ecological signaling cost in communication and show that ecological heterogeneity drives interpopulation variation in both the intensity and the reliability of a sexual signal.

opencc-zeroDec 2016View details →

Data from: MHC-dependent mate preferences in humans

One substantial benefit of sexual reproduction could be that it allows animals (including humans) to react rapidly to a continuously changing environmental selection pressure such as coevolving parasites. This counteraction would be most efficient if the females were able to provide their progeny with certain allele combinations for loci which may be crucial in the parasite-host arms race, for example the MHC (major histocompatibility complex). Here we show that the MHC influences both body odours and body odour preferences in humans, and that the women's preferences depend on their hormonal status. Female and male students were typed for their HLA-A, -B and -DR. Each male student wore a T-shirt for two consecutive nights. The next day, each female student was asked to rate the odours of six T-shirts. They scored male body odours as more pleasant when they differed from the men in their MHC than when they were more similar. This difference in odour assessment was reversed when the women rating the odours were taking oral contraceptives. Furthermore, the odours of MHC-dissimilar men remind the test women more often of their own actual or former mates than do the odours of MHC-similar men. This suggests that the MHC or linked genes influence human mate choice today.

opencc-zeroMay 2019View details →

Data from: Stressor dominance and sensitivity-dependent antagonism: disentangling the freshwater effects of an insecticide among co-occuring agricultural stressors

1. Pesticide concentrations are correlated with regional declines in stream invertebrate diversity. Experimental studies have identified that pesticides can have strong and persistent negative effects on aquatic ecosystems. These effects may occur at concentrations orders of magnitude lower than laboratory toxicity studies predict. Synergism among stressors is one explanation for the observed laboratory-field difference. However, the true effect of pesticides on stream invertebrates remains uncertain, given interactions between stressors and natural environmental conditions. 2. We experimentally examined multiple-stressor effects on stream invertebrate assemblages and leaf-litter breakdown using 24 independent ~900 L re-circulating outdoor mesocosms in a semi-orthogonal design. Two pulses of the pesticide malathion (C10H19O6PS2) were delivered at low and high concentrations (Pulse 1: low at 0.1 and high at 1 µg L-1¬; Pulse 2: at 2.5 and 25 µg L-1). These were crossed with a treatment mimicking the combined stressors from agricultural development; nitrogen, phosphorus and clay (kaolin) sediment (hereafter agricultural stressors). 3. Malathion degradation was rapid (<24 hr half-life) in all treatments, likely because of photolysis, hydrolysis, the presence of biofilms and sorptive processes. There were significant differences in invertebrate assemblages between treatments, where malathion contributed to 48% and 87% of deviance during Pulse 1 and 2 respectively. Malathion had strong negative effects during Pulse 2, decreasing Ephemeroptera, Plecoptera and Trichoptera abundance (P<0.05), invertebrate richness (P<0.01) and total abundance (P<0.01). 4. Despite the dominant effects of malathion on invertebrates, agricultural stressors inhibited rates of leaf litter breakdown (P<0.05), increased invertebrate densities and weakly mitigated malathion toxicity in mesocosms (e.g. PERMANOVA, P≈0.1). Malathion breakdown analysis indicated sediment addition reduced malathion concentrations through alkaline hydrolysis and sorption. Experimental assays on common taxa indicated sediment was antagonistic with malathion. 5. Pesticide effects were not synergistic with the stressors tested here. Indeed, sensitivity-dependent stressor antagonisms were observed, reinforcing a mechanistic understanding of stressor effects and interactions is important. Among aquatic stressors examined, malathion had dominant effects on invertebrate assemblages, despite rapid degradation. Our results suggest that pesticide effects may be underestimated within ecosystems, where pesticides can have severe community wide effects, but rapid pesticide breakdown and sorptive processes may conceal causal links.01-May-2019

Data from: Indirect effects of a large mammalian herbivore on small mammal populations: context-dependent variation across habitat types, mammal species and seasons

Multiple consumer species frequently co-occur in the same landscape and, through effects on surrounding environments, can interact in direct and indirect ways. These interactions can vary in occurrence and importance, and focusing on this variation is critical for understanding the dynamics of interactions among consumers. Large mammalian herbivores are important engineers of ecosystems worldwide, have substantial impacts on vegetation and can indirectly affect small-mammal populations. However, the degree to which such indirect effects vary within the same system has received minimal attention. We used a 16-year-old exclosure experiment, stratified across a heterogeneous landscape, to evaluate the importance of context-dependent interactions between tule elk (Cervus canadensis nannodes) and small mammals [deer mice (Peromyscus maniculatus), meadow voles (Microtus californicus) and harvest mice (Reithrodontymys megalotis)] in a coastal grassland in California. Effects of elk on voles varied among habitats and seasons: in open grasslands, elk reduced vole numbers during fall 2013 but not summer 2014; in Lupinus-dominated grasslands, elk reduced vole numbers during summer 2014 but not fall 2013; and in Baccharis-dominated grasslands, elk had no effect on vole numbers in either season. Effects of elk on the two mice species also varied among habitats and seasons, but often in different ways from voles and each other. In fall 2013, elk decreased mice abundances in Lupinus-dominated grasslands, but not in Baccharis-dominated or open grasslands. In summer 2014, elk decreased the abundance of harvest mice consistently across habitat types. In contrast, elk increased deer-mice numbers in open grasslands but not other habitats. Within the same heterogenous study system, the influence of elk on small mammals was strongly context dependent, varying among habitats, mammal species and seasons. We hypothesize that such variability is common in nature, and that failure to consider it may yield inaccurate findings and limit our understanding of interactions among co-occurring consumers.

opencc-zeroDec 2014View details →

Data from: The good, the bad and the Ulva: the density dependent role of macroalgal subsidies in influencing diversity and trophic structure of an estuarine community

Worldwide, ecological subsidies enhance ecosystem productivity and therefore trophic support for greater biodiversity of taxa. While studies in terrestrial and aquatic ecosystems demonstrate that the magnitude of subsidies into ecosystems differs widely, the thresholds where subsidies may switch from exerting positive to negative effects are poorly understood. In estuaries, eutrophication promotes drift macroalgae that deposit on the benthos, cover intertidal flats for months and serve as pressed resource subsidies for benthic consumers. We hypothesized there would be a critical threshold of macroalgal biomass where ecosystem-level effects would turn from positive to negative. We used manipulative field experiments varying macroalgal mat thickness (0.5, 1.5 and 4 cm) over eight weeks and quantified effects on macrofauna on a lagoon mudflat in California. We documented that plots with mat depths of 0.5 and 1.5 cm had higher diversity by supporting both surface feeding and burrowing detritivores. Non-metric multidimensional scaling showed that the benthic community diverged with mat depth over the course of the experiment. After eight weeks, surface deposit feeders were associated mainly with 0.5 cm macroalgal subsidies, whereas subsurface deposit feeding capitellids were closely linked with 4 cm mats. Depth profiles of pore water sulfide concentration collected from 4 cm mats were 7622 ± 5294 μM, mean ± s.e., (mean of means across depth profiles), whereas 0.5 cm treatments resulted in sulfide concentrations that were 0.25% of the 4 cm treatments. This suggests that the mechanism of negative effects for elevated macroalgal subsidies was development of anoxic conditions promoting sulfide accumulation. Thus, our study was the first to find a critical threshold, or ecological tipping point, beyond which the effects of anthropogenically enhanced subsidies to estuarine mudflat communities switched from positive to negative and to describe the mechanism by which elevated subsides altered the abiotic environment and likely reduced ecosystem functioning.

Data from: Higher rates of pre‐breeding condition gain positively impacts clutch size: a mechanistic test of the condition‐dependent individual optimization model

1. A combination of timing of and body condition (i.e., mass) at arrival on the breeding grounds interact to influence the optimal combination of the timing of reproduction and clutch size in migratory species. This relationship has been formalized by Rowe et al. in a condition-dependent individual optimization model (American Naturalist, 1994, 143, 689-722), which has been empirically tested and validated in avian species with a capital-based breeding strategy. 2. This model makes a key, but currently untested prediction; that variation in the rate of body condition gain will shift the optimal combination of laying date and clutch size. This prediction is essential because it implies that individuals can compensate for the challenges associated with late timing of arrival or poor body condition at arrival on the breeding grounds through adjustment of their life history investment decisions, in an attempt to maximize fitness. 3. Using an 11-year data set in arctic-nesting common eiders (Somateria mollissima), quantification of fattening rates using plasma triglycerides (an energetic metabolite), and a path analysis approach, we test this prediction of this optimization model; controlling for arrival date and body condition, females that fatten more quickly will adjust the optimal combination of lay date and clutch size, in favour of a larger clutch size. 4. As predicted, females fattening at higher rates initiated clutches earlier and produced larger clutch sizes, indicating that fattening rate is an important factor in addition to arrival date and body condition in predicting individual variation in reproductive investment. However, there was no direct effect of fattening rate on clutch size (i.e., birds laying on the same date had similar clutch sizes, independent of their fattening rate). Instead, fattening rate indirectly affected clutch size via earlier lay dates, thus not supporting the original predictions of the optimization model. 5. Our results demonstrate that variation in the rate of condition gain allows individuals to shift flexibly along the seasonal decline in clutch size to presumably optimize the combination of laying date and clutch size.

opencc-zeroDec 2012View details →

Data from: Scale-dependent shifts in the species composition of flower visitors with changing floral density

Responses of flower-visiting animals to floral density can alter interactions between plants, influencing a variety of biological processes, including plant population dynamics and the evolution of flowering phenology. Many studies have found effects of floral or plant density on pollinator visitation rates at patch scales, but little is known about responses of flower visitors to floral densities at larger scales. Here, I present data from an observational field study in which I measured the effects of floral density on visitation to the annual composite Holocarpha virgata at both patch (4 m(2)) and site (12.6 ha) spatial scales. The species composition of flower visitors changed with floral density, and did so in different ways at the two scales. At the site scale, average floral density within patches of H. virgata or within patches of all summer-flowering species combined had a significant positive effect on per-flowerhead visitation by the long-horned bee Melissodes lupina and no significant effects on visitation by any other taxa. At the patch scale, per-flowerhead visitation by honeybees significantly increased whereas visitation by M. lupina often decreased with increasing floral density. For both species, responses to patch-scale floral density were strongest when site-scale floral density was high. The scale-dependence of flower visitor responses to floral density and the interactions between site- and patch-scale effects of floral density observed in this study underscore the importance of improving our understanding of pollinators' responses to floral density at population scales.

Data from: The thermal dependency of locomotor performance evolves rapidly within an invasive species

Biological invasions can stimulate rapid shifts in organismal performance, via both plasticity and adaptation. We can distinguish between these two proximate mechanisms by rearing offspring from populations under identical conditions, and measuring their locomotor abilities in standardized trials. We collected adult cane toads (Rhinella marina) from invasive populations that inhabit regions of Australia with different climatic conditions. We bred those toads, and raised their offspring under common-garden conditions before testing their locomotor performance. At high (but not low) temperatures, offspring of individuals from a hotter location (northwestern Australia) outperformed offspring of conspecifics from a cooler location (northeastern Australia). This disparity indicates that, within less than 100 years, thermal performance in cane toads has adapted to the novel abiotic challenges that cane toads have encountered during their invasion of tropical Australia.

opencc-zeroDec 2016View details →

Data from: Age-dependent trajectories differ between within-pair and extra-pair paternity success

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous, but genetically polygamous species, this generates the interesting possibility of differential trajectories of within-pair and extra-pair siring success with age in males. We investigate these relationships simultaneously using within-individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within- and extra-pair paternity success increased with age, followed by a senescence-like decline. However, the age trajectories of within- and extra-pair paternity successes differed significantly, with the extra-pair paternity success increasing faster, albeit non-significantly so, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within-pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age-dependent payoffs. Males may partition their reproductive effort between within- and extra-pair matings depending on their current age in order to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age-specific mortality may explain the variation in rates of extra-pair paternity observed within and between-species.

opencc-zeroDec 2015View details →

Data from: Context-dependent seed dispersal by a scatter-hoarding corvid

1. Corvids (crows, jays, magpies and nutcrackers) are important dispersers of large-seeded plants. Studies on captive or supplemented birds suggest that they flexibly adjust their scatter-hoarding behaviour to the context of social dynamics and relative seed availability. Because many corvid-dispersed trees show high annual variation in seed production, context-dependent foraging can have strong effects on natural corvid scatter-hoarding behaviour. 2. We investigated how seed availability and social dynamics affected scatter-hoarding in the island scrub jays (Aphelocoma insularis). We quantified rates of scatter-hoarding behaviour and territorial defence of 26 colour-marked birds over a three-year period with variable acorn crops. 3. We tested whether caching parameters were correlated with variation in annual seed production of oaks as predicted by the predator dispersal hypothesis, which states that caching rates and distances should vary with seed abundance in ways that benefit tree fitness. We also tested whether antagonistic interactions with conspecifics would affect scatter-hoarding adversely, as found in experimental studies. 4. Caching behaviour varied with acorn availability. Caching distances correlated positively with annual acorn crop size, increasing by as much as 40% between years. Caching rates declined over time in years with small acorn crops, but increased when crops were large. Acorn foraging and caching rates were also negatively correlated with rates of territorial aggression. Overall foraging rates, however, were not associated with aggression, suggesting that reduced dispersal rates were not simply due to time constraints. 5. Our field results support laboratory findings that caching rates and distances by scatter-hoarding corvids are context-dependent. Furthermore, our results are consistent with predictions of the predator dispersal hypothesis and suggest that large seed crops and social interactions among scatter-hoarders affect dispersal benefits for oaks and other masting tree species.

Data from: Direct evidence that density-dependent regulation underpins the temporal stability of abundant species in a diverse animal community

To understand how ecosystems are structured and stabilized, and to identify when communities are at risk of damage or collapse, we need to know how the abundances of the taxa in the entire assemblage vary over ecologically meaningful timescales. Here, we present an analysis of species temporal variability within a single large vertebrate community. Using an exceptionally complete 33-year monthly time series following the dynamics of 81 species of fishes, we show that the most abundant species are least variable in terms of temporal biomass, because they are under density-dependent (negative feedback) regulation. At the other extreme, a relatively large number of low abundance transient species exhibit the greatest population variability. The high stability of the consistently common high abundance species—a result of density-dependence—is reflected in the observation that they consistently represent over 98% of total fish biomass. This leads to steady ecosystem nutrient and energy flux irrespective of the changes in species number and abundance among the large number of low abundance transient species. While the density-dependence of the core species ensures stability under the existing environmental regime, the pool of transient species may support long-term stability by replacing core species should environmental conditions change.