The effects of paternal reproductive tactic and rearing environment on juvenile variation in growth as mediated through aggression and foraging behaviours of Chinook salmon (Oncorhynchus tshawytscha)

In species with indeterminate growth, differential growth rates can lead to animals adopting alternative reproductive tactics such as sneak–guard phenotypes, which is partially predicted by variation in growth during the juvenile life‐history stage. To investigate sources of growth variation, we examined the independent and joint effects of paternal reproductive tactic (G) and rearing environment (E) on juvenile growth in Chinook salmon (Oncorhynchus tshawytscha), hypothesizing G and E effects are partially mediated through differences in behaviour such as aggressive interactions and resulting foraging behaviours. We created maternal half‐sibling families with one‐half of the female's eggs fertilized by the milt of a sneaker “jack” and the other half by a guarder “hooknose”. At the exogenous feeding stage, each split‐clutch family was then divided again and reared in a rationed diet or growth‐promotion diet environment for approximately 6 months, during which growth parameters were measured. Before saltwater transfer at 9 months of age, social interactions were observed in groups of six fish of various competitor origins. We found ration restricts growth rate and juvenile mass, and evidence of genetic effects on growth depensation, where jack‐sired individuals grew less uniformly over time. These growth‐related differences influenced an individual's level of aggression, with individuals raised on a restricted diet and those whose families experienced greatest growth being most aggressive. These individuals were more likely to feed than not and feed most often. Jack‐sired individuals were additionally aggressive in the absence of food, and when raised on a rationed diet outcompeted others to feed most. These results show how individuals may achieve higher growth rates via intrinsic (G) or induced (E) aggressive behavioural phenotypes, and eventually attain the threshold body size necessary during the saltwater phase to precociously sexually mature and adopt alternative reproductive phenotypes.     

Facilitation can increase the phylogenetic diversity of plant communities

With the advent of molecular phylogenies the assessment of community assembly processes has become a central topic in community ecology. These processes have focused almost exclusively on habitat filtering and competitive exclusion. Recent evidence, however, indicates that facilitation has been important in preserving biodiversity over evolutionary time, with recent lineages conserving the regeneration niches of older, distant lineages. Here we test whether, if facilitation among distant-related species has preserved the regeneration niche of plant lineages, this has increased the phylogenetic diversity of communities. By analyzing a large worldwide database of species, we showed that the regeneration niches were strongly conserved across evolutionary history. Likewise, a phylogenetic supertree of all species of three communities driven by facilitation showed that nurse species facilitated distantly related species and increased phylogenetic diversity.     

The Predatory Mite Phytoseiulus persimilis Adjusts Patch-leaving to Own and Progeny Prey Needs

Integration of optimal foraging and optimal oviposition theories suggests that predator females should adjust patch leaving to own and progeny prey needs to maximize current and future reproductive success. We tested this hypothesis in the predatory mite Phytoseiulus persimilis and its patchily distributed prey, the two-spotted spider mite Tetranychus urticae. In three separate experiments we assessed (1) the minimum number of prey needed to complete juvenile development, (2) the minimum number of prey needed to produce an egg, and (3) the ratio between eggs laid and spider mites left when a gravid P. persimilis female leaves a patch. Experiments (1) and (2) were the pre-requirements to assess the fitness costs associated with staying or leaving a prey patch. Immature P. persimilis needed at least 7 and on average 14±3.6 (SD) T. urticae eggs to reach adulthood. Gravid females needed at least 5 and on average 8.5±3.1 (SD) T. urticae eggs to produce an egg. Most females left the initial patch before spider mite extinction, leaving prey for progeny to develop to adulthood. Females placed in a low density patch left 5.6±6.1 (SD) eggs per egg laid, whereas those placed in a high density patch left 15.8±13.7 (SD) eggs per egg laid. The three experiments in concert suggest that gravid P. persimilis females are able to balance the trade off between optimal foraging and optimal oviposition and adjust patch-leaving to own and progeny prey needs.     

Knowing your habitat: linking patch-encounter rate and patch exploitation in parasitoids

According to optimal foraging theory, animals should decidewhether or not to leave a resource patch by comparing the currentprofitability of the patch with the expected profitability ofsearching elsewhere in the habitat. Although there is abundantevidence in the literature that foragers in general are wellable to estimate the value of a single resource patch, theirdecision making has rarely been investigated with respect tohabitat quality. This is especially true for invertebrates.We have conducted experiments to test whether parasitic waspsadjust patch residence time and exploitation in relation tothe abundance of patches within the environment. We used thebraconid Asobara tabida, a parasitoid of Drosophila larvae,as our model species. Our experiments show that these waspsreduce both the residence time and the degree of patch exploitationwhen patches become abundant in their environment, as predictedby optimal foraging models. Based upon a detailed analysis ofwasp foraging behavior, we discuss proximate mechanisms thatmight lead to the observed response. We suggest that parasitoidsuse a mechanism of sensitization and desensitization to chemicalsassociated with hosts and patches, in order to respond adaptivelyto the abundance of patches within their environment.     

Main stem and off‐channel habitat use by juvenile Chinook salmon in a sub‐Arctic riverscape

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Estimating the long-term repeatability of food-hoarding behaviours in an avian predator

Food-hoarding behaviour is widespread in the animal kingdom and enables predictable access to food resources in unpredictable environments. Within species, consistent variation among individuals in food-hoarding behaviours may indicate the existence of individual strategies, as it likely captures intrinsic differences in how individuals cope with risks (e.g. starvation, pilferage). Using 17 years of data, we estimated the long-term repeatability of 10 food-hoarding behaviours in a population of Eurasian pygmy owls (Glaucidium passerinum), a small avian predator subject to high temporal fluctuations in its main prey abundance. We found low repeatability in the proportion of shrews and the average prey mass stored for both sexes, while females were moderately repeatable in the mass and the number of prey items stored. These two pairs of behaviours were tightly correlated among individuals and might represent two different sets of individual strategies to buffer against starvation risks.     

Foraging Area Marking in Two Related Tetramorium Ant Species (Hymenoptera: Formicidae)

The related ants Tetramorium caespitum and T. impurum mark their foraging area in a species-specific, home range and short-lasting manner. Indeed, ants reaching a new area have a slow linear speed which increases during the marking. Conspecific ants are arrested and attracted by marked areas, while heterospecific ants are reluctant to visit them. However, when the latter do visit marked areas, they move more quickly and less sinuously than conspecific ants and do not stay on the areas. The marking is performed in about 3 min by T. caespitum and in 3 to 6 min by T. impurum. If not reinforced, the marking vanishes in the same time intervals. Neither poison gland nor last sternite extracts reproduce the activity of naturally marked areas, whereas a Dufour gland extract does exactly that. Foraging ants touch the ground with the tip of their gaster. Consequently, we can postulate that the workers mark their foraging area with the contents of this gland, which is associated with the sting apparatus, and that they deposit with the extremity of the gaster. Alien conspecific ants are seldom aggressive to one another, even on marked areas. When encountering each other on unmarked areas, heterospecific ants present some aggressive reactions. On marked areas, their aggressiveness is enhanced and intruder ants are restless, while resident ones walk freely. On ground marked by T. impurum, ants of this species are more aggressive than antagonistic T. caespitum workers. The marking of foraging areas thus induces defense against heterospecifics but not against conspecific ants.     

Short‐term prey field lability constrains individual specialisation in resource selection and foraging site fidelity in a marine predator

Spatio‐temporally stable prey distributions coupled with individual foraging site fidelity are predicted to favour individual resource specialisation. Conversely, predators coping with dynamic prey distributions should diversify their individual diet and/or shift foraging areas to increase net intake. We studied individual specialisation in Scopoli's shearwaters (Calonectris diomedea) from the highly dynamic Western Mediterranean, using daily prey distributions together with resource selection, site fidelity and trophic‐level analyses. As hypothesised, we found dietary diversification, low foraging site fidelity and almost no individual specialisation in resource selection. Crucially, shearwaters switched daily foraging tactics, selecting areas with contrasting prey of varying trophic levels. Overall, information use and plastic resource selection of individuals with reduced short‐term foraging site fidelity allow predators to overcome prey field lability. Our study is an essential step towards a better understanding of individual responses to enhanced environmental stochasticity driven by global changes, and of pathways favouring population persistence.     

Inter-population variation in the behaviour of adult and juvenile Red-footed Boobies Sula sula

Early life is a critical phase of the life cycle of animals and is attracting increased attention because little information is available on the behaviour of young individuals during this period. Behaviour during early life is probably influenced by the environmental conditions encountered by young animals, but data on intraspecific variation between breeding sites during this crucial period of life are limited. Here we study variability in the foraging behaviour of juveniles and adults in three colonies of a pantropical seabird, the Red-footed Booby Sula sula. Both adults and juveniles were measured and fitted with GPS loggers in three remote islands: Genovesa (Galapagos, Eastern Pacific Ocean), Europa (Western Indian Ocean) and Surprise (New Caledonia, Western Pacific Ocean). Foraging behaviour was compared between age-classes, sex and colonies by examining trip characteristics, different behaviours at sea, potential associations between individuals and morphological characteristics. Compared with adults, juveniles conducted shorter trips that were restricted to around the colony, especially on Genovesa (max. range: 203.4 ± 125.1 km and 3.6 ± 3.1 km, respectively). Juveniles appeared more constrained by poor flight skills and experience rather than by their morphology. Adults travelled 45% of the time during at-sea trips, whereas juveniles spent a a lower proportion of time travelling but foraged more often using an ‘area-restricted search’ behaviour, potentially training to catch prey. Associations between juveniles were commonly detected in the three colonies and occurred mostly during foraging, suggesting that social learning is an important strategy. Variability of morphometric measurements in both adults and juveniles was high between sites, with larger birds found on Genovesa. These results suggest that adaptations to local environmental conditions are already visible in their early life. Future studies should continue to investigate the behavioural flexibility of juvenile birds to better understand the effect of local environmental conditions during this critical stage of life.