Nest predation risk and growth strategies of passerine species: grow fast or develop traits to escape risk?

Abstract Different body components are thought to trade off in their growth and development rates, but the causes for relative prioritization of any trait remains a critical question. Offspring of species at higher risk of predation might prioritize development of locomotor traits that facilitate escaping risky environments over growth of mass. We tested this possibility in 12 altricial passerine species that differed in their risk of nest predation. We found that rates of growth and development of mass, wings, and endothermy increased with nest predation risk across species. In particular, species with higher nest predation risk exhibited relatively faster growth of wings than of mass, fledged with relatively larger wing sizes and smaller mass, and developed endothermy earlier at relatively smaller mass. This differential development can facilitate both escape from predators and survival outside of the nest environment. Tarsus growth was not differentially prioritized with respect to nest predation risk, and instead all species achieved adult tarsus size by age of fledging. We also tested whether different foraging modes (aerial, arboreal, and ground foragers) might explain the variation of differential growth of locomotor modules, but we found that little residual variation was explained. Our results suggest that differences in nest predation risk among species are associated with relative prioritization of body components to facilitate escape from the risky nest environment.     

The arctic fox Alopex lagopus in Fennoscandia: a victim of human-induced changes in interspecific competition and predation?

After a marked decline at the beginning of the 1900s, the arctic fox Alopex lagopus population in Fennoscandia has remained at a very low level. We suggest that the main cause for the population crash was winter starvation caused by (1) over-hunting of reindeer Rangifer tarandus populations, and thus reduced carcass availability in the mountains, and (2) increased interspecific competition for these carcasses because of increased invasion of red foxes Vulpes vulpes from lower altitudes. The failure of arctic fox populations to recover, despite increasing reindeer populations in the mid 1900s, can be explained by a concurrent strong increase in red fox numbers. Analyses of countywide hunting statistics from Norway 1891–1920 suggest that there actually was an increase in red fox numbers in the period of arctic fox decline, and that the increase in reindeer populations from the 1920s to the 1950s was accompanied by a new increase in red fox numbers. We conclude that restoring arctic fox populations most likely will require a substantial and lasting reduction of red fox populations.     

Correlation between male size and territory quality: consequence of male competition or predation susceptibility?

Territory characteristics correlate with male characteristics in several species. This can result from male competition for the best territories, or from males varying in their ability to pay other costs of territoriality, such as predation risk costs. In a population of threespine sticklebacks, Gasterosteus aculeatus , we found the biggest males to defend the biggest territories with a low structural complexity and a high female encounter rate. By experimentally manipulating competition intensity and habitat structure, we show that both male competition and predation exposure influenced the distribution of territories among males. Males increased the size of their territory when a neighbouring male was removed, whereas they reduced their territory when habitat complexity and cover from predators were reduced, with large males reducing their territory size less than smaller males. This suggests that large males occupy large, open territories both because of their superior competitive ability and because of their either lower predation susceptibility or higher risk-taking. Large, open territories were beneficial in mate attraction and male competition and predation exposure therefore biased mating opportunities towards large males. This suggests that cost of territoriality to males may reduce mate choice costs to females by securing that large males are encountered more often than small males, and by providing an additional cue, territory quality, which indicates which males are worth inspecting.     

Prey habitat selection under shared predation: tradeoffs between risk and competition?

An individual's choice of habitat should optimize amongst conflicting demands in a way that maximizes its fitness. Habitat selection by one species will often be influenced by presence and abundance of competitors that interact directly and indirectly with each other (such as through shared predators). The optimal habitat choice will thus depend on competition for resources by other species that can also modify predation risk. It may be possible to disentangle these two effects with careful analysis of density‐dependent habitat selection by a focal prey species. We tested this conjecture by calculating habitat isodars (graphs of density assuming ideal habitat selection) of chital deer living in two adjoining dry‐forest habitats in Gir National Park and Sanctuary, western India. The habitats differed only in presence (Sanctuary) and absence (National Park) of domestic prey (cattle and buffalo). Both species are preyed on by Asiatic lions. The habitat isodar revealed at low densities, that chital live in small groups and prefer habitat co‐occupied by livestock that reduce food resources, but also reduce predation risk. At higher densities, chital form larger groups and switch their preference toward risky habitat without livestock. The switch in chital habitat use is consistent with theories predicting that prey species should trade off safety in favor of food as population density increases.     

Parasite community structure within and across host populations of a marine pelagic fish: how repeatable is it?

The geographical variation in parasite community structure among populations of the same host species remains one of the least understood aspects of parasite community ecology. Why are parasite communities clearly structured in some host populations, and randomly assembled in others? Here, we address this fundamental question using data on the metazoan parasite communities of different host size-classes of four distinct populations of a small pelagic fish, the Argentine anchovy, Engraulis anchoita, from the South West Atlantic. Within each fish sample, fish length was correlated with both the total intensity of parasites and species richness among infracommunities. More importantly, average fish length correlated with mean infracommunity richness and mean total intensity across the fish samples, indicating that the characteristics of parasite assemblages in a fish population are strongly influenced by the size of its fish in relation to those in other populations. Nested subset patterns were observed in about half of the fish samples. This means that the presence or absence of parasite species among fish individuals is often not random; however, no repeatability of nestedness among component communities was observed. Average fish length did not influence directly the likelihood that a parasite assemblage was significantly nested. However, variables influenced by average fish length, namely mean infracommunity richness and mean total intensity, determine the probability that a nested hierarchy will be observed; host size may thus indirectly affect parasite community structure either itself or via its influence on host movement and feeding patterns. To some extent, this apparent link may be due to the sensitivity of nestedness analyses to the proportion of presence in a presence/absence matrix; this in itself is a biological feature of the parasite community, however, which is associated with mean host length.     

Pelvic anti-predator armour reduction in Norwegian populations of the threespine stickleback: a rare phenomenon with adaptive implications?

In order to search for armour reductions in the anti-predator armour apparatus of the threespine stickleback Gasterosteus aculeatus , we studied populations from 200 coastal lakes and 32 marine and estuarine sites in Norway. We scored the presence of reductions in the pelvic apparatus in these populations, measured the length of the second dorsal fin and pelvic spine and counted lateral plates in a subset of 96 populations. Then we looked for the relation between pelvic reduction and number of lateral plates and lengths of the second dorsal spine and pelvic spine. We also observed whether pelvic reduced fish had asymmetric development on the right or the left side of the pelvis. Pelvic reduction was not found in marine and estuarine sticklebacks (with one single exception), but in freshwater it occurred in four out of 200 lakes. The amount of pelvic reduction differed from 5% to 68% in the four populations. There appears to be a correlation between pelvic reduction and spine lengths at the population level, but not plate number. Further, it appears to be difficult to explain the occurrence of pelvic reduction in Norway with the factors proposed to be responsible for pelvic reduction in other regions.     

Non‐consumptive effects of predation: does perceived risk strengthen the genetic integration of behaviour and morphology in stickleback?

Predators can shape genetic correlations in prey by altering prey perception of risk. We manipulated perceived risk to test whether such non‐consumptive effects tightened behavioural trait correlations in wild‐caught stickleback from high‐ compared to low‐risk environments due to genetic variation in plasticity. We expected tighter genetic correlations within perceived risk treatments than across them, and tighter genetic correlations in high‐risk than in low‐risk treatments. We identified genetic variation in plasticity, with genetic correlations between boldness, sociality, and antipredator morphology, as expected, being tighter within treatments than across them, for both of two populations. By contrast, genetic correlations did not tighten with exposure to risk. Tighter phenotypic correlations in wild stickleback may thus arise because predators induce correlational selection on environmental components of these traits, or because predators tighten residual correlations by causing environmental heterogeneity that is controlled in the laboratory. Our study places phenotypic integration firmly into an ecological context.     

Contrasting levels of extra-pair paternity in mainland and island populations of the house sparrow (Passer domesticus): is there an 'island effect'?

Despite the many studies that have investigated the genetic mating system of socially monogamous birds, very little is known about the underlying causes of extra-pair paternity and few studies have attempted to test those hypotheses which have been suggested. This study describes die analysis of die genetic mating system of two populations of the house sparrow [Passer domesticus) , and uses the results from four other populations to test existing hypodieses using an intra-specific comparative approach. The parentage analysis was conducted using a combination of published and newly presented microsatellite loci isolated from the house sparrow. One population in Kentucky, U.S.A. was found to contain what may be considered to be a typical level of extra-pair paternity for mis species (10.5%, 19/185 offspring). The second, a population on the island of Lundy, UK, exhibited a very low level (1.3%, 4/305 offspring), significandy lower dian that in all the other populations studied so far. The finding of such diverse rates of extra-pair paternity, along with the existing estimates from ofher populations, has allowed us to test the effects of breeding density and genetic variation on die level of extra-pair paternity. We found no effect of either factor on the frequency of extra-pair paternity in the house sparrow, leaving the cause of this variation open to fresh ideas.     

Abiotic factors,competition or predation: what determines the distribution of young crayfish in a watershed?

In the headwaters of the New River in western North Carolina, the dominant crayfish species changes with increasing stream size. One transition occurs between third- and fourth-order streams. Cambarus chasmodactylus is the dominant species in third-order tributaries. Orconectes cristavarius is the dominant species in the fourth-order South Fork of the New River. While adult C. chasmodactylus are present in the South Fork, the young-of-the-year (YOY) of this species are absent despite evidence of reproduction. In this study we evaluated the factors that may be responsible for the absence of C. chasmodactylus YOY from the South Fork. A field experiment was used to evaluate the role of abiotic factors and competition with YOY O. cristavarius. There was no significant effect of either of these factors on mortality or growth of C. chasmodactylus YOY. The growth rate of O. cristavarius was 3× faster than that of C. chasmodactylus in this experiment. Since neither abiotic factors nor competition appeared responsible for the exclusion of C. chasmodactylus YOY from the South Fork we evaluated the potential importance of selective predation by rock bass (Ambloplites rupestris), a fish species that is common in the South Fork but virtually absent in the tributaries. In a laboratory experiment, C. chasmodactylus YOY experienced significantly higher mortality than O. cristavarius YOY in the presence of rock bass. Field observations and a laboratory experiment suggest that the two crayfish species differ in their anti-predator behaviors. Cambarus chasmodactylus was less likely to swim when initially disturbed and swam shorter distances than O. cristavarius. The differences in escape behavior and growth rate may contribute to the differences in the vulnerability of the two species to rock bass predation. Our results suggest that intense predation pressure exerted by the rock bass may contribute to the virtual exclusion of C. chasmodactylus YOY from the fourth-order South Fork. Handling editor: J. Trexler     

Genetic variation and structure of house sparrow populations: is there an island effect?

Population genetic structure and intrapopulation levels of genetic variation have important implications for population dynamics and evolutionary processes. Habitat fragmentation is one of the major threats to biodiversity. It leads to smaller population sizes and reduced gene flow between populations and will thus also affect genetic structure. We use a natural system of island and mainland populations of house sparrows along the coast of Norway to characterize the different population genetic properties of fragmented populations. We genotyped 636 individuals distributed across 14 populations at 15 microsatellite loci. The level of genetic differentiation was estimated using F‐statistics and specially designed Mantel tests were conducted to study the influence of population type (i.e. mainland or island) and geographic distance on the genetic population structure. Furthermore, the effects of population type, population size and latitude on the level of genetic variation within populations were examined. Our results suggest that genetic processes on islands and mainland differed in two important ways. First, the intrapopulation level of genetic variation tended to be lower and the occurrence of population bottlenecks more frequent on islands than the mainland. Second, although the general level of genetic differentiation was low to moderate, it was higher between island populations than between mainland populations. However, differentiation increased in mainland populations somewhat faster with geographical distance. These results suggest that population bottleneck events and genetic drift have been more important in shaping the genetic composition of island populations compared with populations on the mainland. Such knowledge is relevant for a better understanding of evolutionary processes and conservation of threatened populations.     

Evolution of embryonic developmental period in the marine bird families Alcidae and Spheniscidae: roles for nutrition and predation?

Background  

Nutrition and predation have been considered two primary agents of selection important in the evolution of avian life history traits. The relative importance of these natural selective forces in the evolution of avian embryonic developmental period (EDP) remain poorly resolved, perhaps in part because research has tended to focus on a single, high taxonomic-level group of birds: Order Passeriformes. The marine bird families Alcidae (auks) and Spheniscidae (penguins) exhibit marked variation in EDP, as well as behavioural and ecological traits ultimately linked to EDP. Therefore, auks and penguins provide a unique opportunity to assess the natural selective basis of variation in a key life-history trait at a low taxonomic-level. We used phylogenetic comparative methods to investigate the relative importance of behavioural and ecological factors related to nutrition and predation in the evolution of avian EDP.     

In situ versus laboratory estimations of length–weight regression and growth rate of Daphnia magna (Branchiopoda, Anomopoda) from an aerated waste stabilization pond

The present paper questions the adequacy of using length–weight regressions and growth rates calculated in the laboratory under constant physico-chemical and food conditions for the estimation of biomass and secondary production of animals living in a variable environment from the physico-chemistry and food availability point of view. Length–weight regressions (LWR) and growth rate of Daphnia magna were determined in situat five key periods of the year. In parallel, LWR and growth rate were determined in laboratory incubators at temperature adjusted to the mean temperature measured during the in situexperiments. LWR estimated from pond daphnids collected during the in situ experiments were, on the whole, not significantly different from LWR established during laboratory experiments, indicating that the food availability was globally similar in the laboratory and in situexperiments, even though food items were substantially different between the experiments. In situ algal biomass was indeed low compared to the algal biomass in laboratory experiments, but high biomasses of bacteria, protozoa and detritus were available for daphnid feeding in the tubes incubated in situ. Growth rate of D. magnawas monitored in situusing 50-ml tubes closed with Nylon net (mesh size = 80 m) and in the laboratory using 50-ml glass flasks. The physico-chemical, bacteriological and algological variables were checked to be similar in the tubes and in the pond. Growth rates varied according to the size of the animal and according to the water temperature. The maximum growth rates were observed for juveniles at 20.2 °C. Growth rates were also determined in the laboratory at temperature corresponding to the mean temperature recorded in the pond during the in situ growth experiments. Differences between in situ and laboratory body length–growth rate regressions (LgR) were observed for the experiments conducted at 15.6 °C and 23.6 °C. Due to differences in LWR and LgR between in situ and laboratory experiments, biomass and daily production estimated from laboratory cultures were found to be significantly, but not severely, higher than biomass and daily production estimated on the basis of in situ experiments. It has been, therefore, concluded that, when the constraints linked to the realization of in situ growth experiments are too strong, the laboratory approach is fully justified.     

Grazing and growth responses of a marine oligotrichous ciliate fed with two nanoplankton: does food quality matter for micrograzers?

To investigate whether predator growth and grazing would depend on prey properties besides size, we studied the numerical and functional responses of a marine oligotrichous ciliate isolated in Hong Kong coastal waters, Strobilidium sp., on two nanoplanktonic preys of similar size. The growth and ingestion rates of Strobilidium sp. could be fit with prey concentrations by hyperbolic curves. Strobilidium sp. exhibited higher maximal growth rates and gross growth efficiencies, and lower maximal clearance rates on Nannochloropsis sp. than on Isochrysis galbana. Our results demonstrate that prey properties presumably food quality can have a considerable effect on predator growth and grazing and implications on phytoplankton community structure and biogeochemical cycling.     

Intraguild predation among ladybeetles and a green lacewing: do the larval spines of Curinus coeruleus(Coleoptera: Coccinellidae) serve a defensive function?

Laboratory experiments examined interspecific interactions between larvae of three coccinellid species, Curinus coeruleus Mulsant (Chilocorinae), Harmonia axyridis Pallas and Olla v-nigrum (Mulsant) (Coccinellinae), and between these and larvae of the green lacewing, Chrysoperla rufilabris (Burmeister). Larvae of C. coeruleus, although defended on their dorsal surface with long spines, had the smallest mandibles, were the slowest-moving, and the least successful in interspecific larval combat. The long spines of third instar C. coeruleusappeared to reduce their palatability as food to H. axyridis and O. v-nigrum larvae in choice tests with dead larvae, but were not an effective defence against these species in Petri dish arenas. Larvae of O. v-nigrum had a smooth dorsal surface, were intermediate in terms of mandible size, but were the fastest moving, a trait that benefited their survival in intraguild combat. Larvae of H. axyridis were intermediate with respect to dorsal spines and speed of movement, but had the largest mandibles. This species was the most effective intraguild combatant among the coccinellids and the only one to successfully compete against C. rufilabris larvae of similar age. The speed, manoeuverability and long mandibles of C. rufilabris enabled them to impale coccinellid larvae at a relatively safe distance. The spines of C. coeruleus larvae impeded laterally oriented attacks by C. rufilabris, but did not provide sustained protection from repeated attacks. Success in these interactions appeared largely a function of offensive weaponry (mandible size and morphology) and speed of movement, although the role of dorsal spines as defensive structures was not ruled out. Rates of larval cannibalism were highest for C. rufilabris and largely mirrored the level of aggression observed in interspecific combat for each species.     

Morphological and genetic divergence of intralacustrine stickleback morphs in Iceland: a case for selective differentiation?

The evolutionary processes involved in population divergence and local adaptation are poorly understood. Theory predicts that divergence of adjacent populations is possible but depends on several factors including gene flow, divergent selection, population size and the number of genes involved in divergence and their distribution on the genome. We analyse variation in neutral markers, markers linked to putative quantitative trait loci and morphological traits in a recent (<10000 years) zone of primary divergence between stickleback morphs in Lake Thingvallavatn, Iceland. Environmental factors, especially predation, are clearly implicated in reducing gene flow between morphs. There is continuous morphological and genetic variation between habitats with a zone centre similar to secondary contact zones. Individual microsatellite loci are implicated as being linked to adaptive variation by direct tests as well as by differences in cline shape. Patterns of linkage disequilibria indicate that the morphs have diverged at several loci. This divergence shows parallels and differences with the well-studied limnetic-benthic stickleback morphs, both in phenotypic divergence and at the genomic level.     

Male mating success and risk of predation in a wolf spider: a balance between sexual and natural selection?

1. Traits that benefit males through sexual selection are simultaneously expected to impair males by provoking costs through natural selection. If we consider the two male fitness components, mating success and viability, then we may expect that the increase in male mating success resulting from a larger trait size will be counterbalanced by an increase in viability costs.
2. We studied the benefits and costs of male mate searching and sexual signalling activity in the wolf spider Hygrolycosa rubrofasciata . In the field, males search females actively and court them by drumming dry leaves with their abdomen. Females have been shown to prefer males with high drumming rate. Male moving and especially drumming is energetically highly demanding and drumming results in significant mortality costs.
3. Our objective in this study was to determine whether male mate-searching activity or drumming activity affect male mating success and the risk of males being predated.
4. It was evident that both higher mate-searching activity and higher drumming activity benefited males by increasing their mating success. Higher mate-searching activity clearly impaired males by causing direct increase in predation risk. There was also a slight tendency that more actively drumming males had higher risk of predation and from all of the predated males 13.3% were caught directly after they had drummed. Furthermore, male drumming activity decreased drastically in the presence of the predator.
5. We conclude that in H. rubrofasciata both increased mate-searching activity and drumming activity benefit males through sexual selection, but at the same time natural selection provokes direct balancing costs on the same traits.     

Positive effects of UV radiation on a calanoid copepod in a transparent lake: do competition, predation or food availability play a role?

Zooplankton tolerant to ultraviolet radiation (UVR) could beindirectly affected by UVR through interactions with UV-sensitivespecies in the same ecosystem. In Lake Giles, Pennsylvania,USA, the calanoid copepod Leptodiaptomus minutus is more UVRtolerant than the cohabiting species Daphnia catawba and Cyclopsscutifer. We asked whether L. minutus is affected by UV-inducedmortality of a food competitor (D. catawba) or a predator ofits nauplii (C. scutifer). We conducted two in situ enclosureexperiments with six treatments: L. minutus alone, L . minutus+ Daphnia and L. minutus + Cyclops in the presence and absenceof UVR. There were few differences in survival among treatmentsin Experiment 1, which had enhanced food and a cumulative UVR(320 nm) dose of 9.3 kJ m^–2. In Experiment 2, which hadambient food and a UVR (320 nm) dose of 20.0 kJ m^–2, L.minutus survival and reproduction were higher in the +UVR comparedto –UVR, regardless of competitors or predators. Chlorophylla (Chl a) in Experiment 2 was higher in the +UVR than –UVR.While interactions between zooplankton species of differingUVR tolerances are potentially important, these results insteaddemonstrate that the beneficial UVR effect on L. minutus isindependent of concurrent detrimental UVR effects on competitorsand predators. Further research on the phytoplankton communityis necessary to determine whether UVR alleviates bacterial competition,increases nutrient availability or affects phytoplankton byother mechanisms.