Environmental sensitivity differs between rabbit lines selected for reproductive intensity and longevity

To better understand the mechanisms that allow some animals to sustain their productive effort in harsh environmental conditions, rabbit does from two selection lines (LP and V) were housed in normal (NC), nutritional (NF) or heat (HC) challenging environmental conditions from first to third partum. The LP line (n=85) was founded on reproductive longevity criteria by selecting does from commercial farms that had a minimum of 25 partum with more than 7.5 kits born alive per parity. Line V (n=79) was constituted from four specialised maternal lines into a composite synthetic line and then selected by litter size at weaning for 36 generations. Female rabbits in NC and NF environments were housed at normal room temperature (18°C to 24°C) and fed with control [11.6 MJ digestible energy (DE)/kg dry matter (DM)] or low-energy diets (9.1 MJ DE/kg DM). HC does were housed at high room temperatures (25°C to 35°C) and fed the control diet. Female rabbits in the HC and NF environments ingested 11.5% and 6% less DE than NC does, respectively (P<0.05). These differences between environments occurred in both lines, with the differences being higher for LP than for V does (+6%; P<0.05). Milk yield responses followed those of energy intake also being higher for LP does (+21.3 g/day; P<0.05). The environmental conditions did not affect the perirenal fat thickness (PFT), but a genotype by environment interaction was observed. In NC and HC, the PFT was higher for line V (+0.23 and +0.35 mm, respectively; P<0.05) than for LP does, but this was not the case at NF (−0.01 mm). Moreover, the PFT evolution was different between them. In the NC environment, LP does used the accreted PFT in late lactation (−0.29 mm), whereas V does did not (−0.08 mm). Conversely, in the HC environment, LP does showed a flat PFT evolution in late lactation, whereas V does accumulated PFT. In the NF environment, LP and V does had a similar PFT evolution. There was also a litter size reduction for V does of −2.59 kits total born in HC and −1.78 kits total born in NF environments, whereas this was not observed for LP does. The results for LP does indicate a direct use of DE ingested for reproduction with little PFT change, whereas V does actively use the PFT reserves for reproduction.     

Distinctiveness in the face of gene flow: hybridization between specialist and generalist gartersnakes

Patterns of divergence and polymorphism across hybrid zones can provide important clues as to their origin and maintenance. Unimodal hybrid zones or hybrid swarms are composed predominantly of recombinant individuals whose genomes are patchworks of alleles derived from each parental lineage. In contrast, bimodal hybrid zones contain few identifiable hybrids; most individuals fall within distinct genetic clusters. Distinguishing between hybrid swarms and bimodal hybrid zones can be important for taxonomic and conservation decisions regarding the status and value of hybrid populations. In addition, the causes of bimodality are important in understanding the generation and maintenance of biological diversity. For example, are distinct clusters mostly reproductively isolated and co‐adapted gene complexes, or can distinctiveness be maintained by a few ‘genomic islands’ despite rampant gene flow across much of the genome? Here we focus on three patterns of distinctiveness in the face of gene flow between gartersnake taxa in the Great Lakes region of North America. Bimodality, the persistence of distinct clusters of genotypes, requires strong barriers to gene flow and supports recognition of distinct specialist (Thamnophis butleri) and generalist (Thamnophis radix) taxa. Concordance of DNA‐based clusters with morphometrics supports the hypothesis that trophic morphology is a key component of divergence. Finally, disparity in the level of differentiation across molecular markers (amplified fragment length polymorphisms) indicates that distinctiveness is maintained by strong selection on a few traits despite high gene flow currently or in the recent past.     

The functional trophic role of lotic primary consumers: generalist versus specialist strategies

1. The relative extent of generalist or specialist resource use strategies is an important question in ecology. A community dominated by specialist strategies suggests a high level of interspecific competition for resources, resulting in the evolutionary development of isolating mechanisms between species (e.g. resource specialization to avoid and/or outcompete other species). A community dominated by generalist strategies suggests less interspecific competition for resources, allowing many taxa to utilize the same resources. In stream systems, generalist food habits are a common strategy among primary consumers, but little is known about resource assimilation strategies (resources incorporated into tissue growth). Published data indicate that generalist resource assimilation strategies may prevail in lotic systems as well.
2. Functional feeding groups (FFGs) are often used to infer resource assimilation among lotic macroinvertebrates (e.g. shredder-detritivore, scraper-herbivore). While these groupings are aptly used to describe invertebrate feeding modes and community structure, the use of FFGs to describe resource assimilation among lotic consumers is not appropriate. Sufficient data now exist to seriously question how accurately FFG assignments describe the processes of energy flow and material transfer between trophic levels in stream ecosystems.
3. Because FFGs may not accurately describe functional attributes in lotic systems, an alternative approach is needed. One approach is to determine the amount of secondary production that is derived from autochthonous (e.g. periphyton and algae) and allochthonous (e.g. detritus) resources directly. A simple model of community function based on this approach is presented. The model incorporates trophic generalists into measurement of consumer–resource energetics in lotic systems.     

The functional trophic role of lotic primary consumers: generalist versus specialist strategies

1. The relative extent of generalist or specialist resource use strategies is an important question in ecology. A community dominated by specialist strategies suggests a high level of interspecific competition for resources, resulting in the evolutionary development of isolating mechanisms between species (e.g. resource specialization to avoid and/or outcompete other species). A community dominated by generalist strategies suggests less interspecific competition for resources, allowing many taxa to utilize the same resources. In stream systems, generalist food habits are a common strategy among primary consumers, but little is known about resource assimilation strategies (resources incorporated into tissue growth). Published data indicate that generalist resource assimilation strategies may prevail in lotic systems as well.
2. Functional feeding groups (FFGs) are often used to infer resource assimilation among lotic macroinvertebrates (e.g. shredder-detritivore, scraper-herbivore). While these groupings are aptly used to describe invertebrate feeding modes and community structure, the use of FFGs to describe resource assimilation among lotic consumers is not appropriate. Sufficient data now exist to seriously question how accurately FFG assignments describe the processes of energy flow and material transfer between trophic levels in stream ecosystems.
3. Because FFGs may not accurately describe functional attributes in lotic systems, an alternative approach is needed. One approach is to determine the amount of secondary production that is derived from autochthonous (e.g. periphyton and algae) and allochthonous (e.g. detritus) resources directly. A simple model of community function based on this approach is presented. The model incorporates trophic generalists into measurement of consumer–resource energetics in lotic systems.     

Ecological preference between generalist and specialist rodents: spatial and environmental correlates of phenotypic variation

Different ecological preferences among species may result in differences in response to similar environmental variation. To test this hypothesis, we assessed the patterns of skull and mandible size and shape variation in three Sigmodontinae mice from agroecosystems of central Argentina with increasing degree of specialization: Calomys musculinus, Akodon azarae and Oxymycterus rufus. Spatial patterns in size and shape were analysed after controlling for allometry and sexual dimorphism using a total of 697 specimens. We then evaluated the covariation between shape, climatic and environmental variables and assessed the contribution of distinct climatic and environmental variables to phenotypic variability. Oxymycterus rufus displayed a marked spatial structure, and there was a high correlation between shape, climatic and environmental variables in this species. Climatic and environmental variables had a moderate effect on the phenotype of A. azarae, and were not correlated with morphological variation in C. musculinus. Our study highlights the difference in phenotypic responses to spatial and environmental gradients across coexisting species, specialist species displaying a more marked spatial structure in morphology than generalist species. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 180–203.     

Differential habitat use promotes sustainable coexistence between the specialist otter and the generalist mink

Optimal foraging and habitat selection theories predict that heterogeneous environments should favour the coexistence of competitors, especially when the dominant competitor is a specialist and the sub-ordinate is a generalist. In this paper, we analysed differential habitat use as a potential mechanism for the coexistence of two competing riparian mammals, the specialist and dominant Eurasian otter ( Lutra lutra ) and the generalist and sub-ordinate American mink ( Mustela vison ). We tested three hypotheses: H1: mink coexist with otters for longer in areas with abundance of habitats hosting terrestrial prey because, by not relying on aquatic prey, mink can segregate from its competitor. H2: the characteristics of the habitat closer to the riverbank will affect the length of time the two species coexist, because mink are still tied to the water even in the presence of otters. H3: denser vegetative cover along the bank increases the duration of coexistence of mink and otters because it reduces the frequency of their encounters. The first hypothesis was supported by the data and we found that in areas where terrestrial prey was abundant mink coexisted for longer with otters. The second hypothesis was also supported by the data and the characteristics of the habitat closer to the riverbank were the most important in determining coexistence time. Finally, we did not find supporting evidence for the third hypothesis. This study provides strong evidence that habitat heterogeneity plays an important role in determining the likelihood of coexistence of American mink with Eurasian otters. This result is particularly important from a conservation standpoint. Mink are invasive and a threat to endangered species in parts of their range. The knowledge that mink have a higher chance to persist in the presence of otters when terrestrial prey is abundant should be used to target areas for preferential mink management.     

Reproductive response of generalist and specialist aphid morphs with the same genotype to plant secondary compounds and amino acids

Many studies have paid particular attention to the role of either secondary plant compounds or amino acids as determinants of host-plant range in phytophagous insects. Here we examine the relative importance of both of these classes of compound in host acceptance by generalist and specialist morphs of the black bean aphid, Aphis fabae, that are morphologically similar and genetically identical. Eleven secondary plant compounds and six amino acids with known biological activity in aphids are presented to insects within an artificial membrane system as single compounds, mixtures of same-class compounds and combined mixtures of the two classes of compound. It is found that 1) when specific single secondary compounds and amino acids are presented to generalist and specialist morphs of A. fabae, differential responses are exclusively consistent with plant-use strategy for amino acids but not for secondary compounds, 2) neither secondary compound nor amino acid mixtures give reproductive responses entirely consistent with plant range, but the response to secondary compounds is broadly consistent with plant range whereas the response to amino acids is not, 3) when secondary compounds and amino acid mixtures are combined, the response to secondary compounds generally dominates that to amino acids. Some scenarios of plant-range determination by secondary plant compounds and amino acids, suggested by results, are discussed.     

The enemy release and EICA hypothesis revisited: incorporating the fundamental difference between specialist and generalist herbivores

The success of invasive plants has been attributed to their escape from natural enemies and subsequent evolutionary change in allocation from defence to growth and reproduction. In common garden experiments with Senecio jacobaea, a noxious invasive weed almost worldwide, the invasive populations from North America, Australia, and New Zealand did indeed allocate more resources to vegetative and reproductive biomass. However, invasive plants did not show a complete change in allocation from defence to growth and reproduction. Protection against generalist herbivores increased in invasive populations and pyrrolizidine alkaloids, their main anti‐herbivore compounds, did not decline in invasive populations but were higher overall compared with native populations. In contrast, invasive plants lost additional protection against specialist herbivores adapted to pyrrolizidine alkaloids. Hence, the absence of specialist herbivores in invasive populations resulted in the evolution of lower protection against specialists and increased growth and reproduction, but also allowed a shift towards higher protection against generalist herbivores.     

Partitioning of resources: the evolutionary genetics of sexual conflict over resource acquisition and allocation

Fitness depends on both the resources that individuals acquire and the allocation of those resources to traits that influence survival and reproduction. Optimal resource allocation differs between females and males as a consequence of their fundamentally different reproductive strategies. However, because most traits have a common genetic basis between the sexes, conflicting selection between the sexes over resource allocation can constrain the evolution of optimal allocation within each sex, and generate trade‐offs for fitness between them (i.e. ‘sexual antagonism’ or ‘intralocus sexual conflict’). The theory of resource acquisition and allocation provides an influential framework for linking genetic variation in acquisition and allocation to empirical evidence of trade‐offs between distinct life‐history traits. However, these models have not considered the emergence of trade‐offs within the context of sexual dimorphism, where they are expected to be particularly common. Here, we extend acquisition–allocation theory and develop a quantitative genetic framework for predicting genetically based trade‐offs between life‐history traits within sexes and between female and male fitness. Our models demonstrate that empirically measurable evidence of sexually antagonistic fitness variation should depend upon three interacting factors that may vary between populations: (1) the genetic variances and between‐sex covariances for resource acquisition and allocation traits, (2) condition‐dependent expression of resource allocation traits and (3) sex differences in selection on the allocation of resource to different fitness components.     

Conservation implications of competition between generalist and specialist rodents in Mediterranean afforested landscape

Density dependent habitat selection at the community level is regarded as a major determinant of biodiversity at the local scale, and data on these processes and how they are affected by human activities is highly applicable to conservation. By studying the competitive relationships between a specialist and a generalist we can acquire valuable insights about how different environmental elements determine species abundance and distribution and consequently biodiversity. Here we describe a study of density dependent processes that determine the community structure of two rodents: a specialist—the broad toothed mouse (Apodemus mystacinus), and a generalist—the common spiny mouse (Acomys cahirinus) in a Mediterranean maqui habitat, and how this structure is impacted by anthropogenic planting of pine stands. We carried out two field experiments: The first, based on open field trapping, looking at how rodent communities change with habitat structure. The second experiment was an enclosure study aimed at validating the habitat preferences and competitive relationship between the specialist and the generalist. We identified asymmetric competition relationships in which the specialist was dominant over the generalist. Competition intensity was lower in maqui with >10% oak cover, although both species abundances were high. Competition was found only during the limiting season (summer). Based on these findings we produced management recommendations to keep indigenous small mammals’ biodiversity high. Density dependent habitat selection processes play a central role in determining biodiversity, and understanding the mechanisms motivating these processes is needed if alterations in biodiversity in response to human disturbance are to be understood.     

Interaction of glucosinolate content of Arabidopsis thaliana mutant lines and feeding and oviposition by generalist and specialist lepidopterans

The diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), is an insect specialized on glucosinolate-containing Brassicaceae that uses glucosinolates in host-plant recognition. We used wild-type and mutants of Arabidopsis thaliana (L.) Heynh. (Brassicaceae) to investigate the interaction between plant glucosinolate and myrosinase content and herbivory by larvae of the generalist Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) and the specialist P. xylostella. We also measured glucosinolate changes as a result of herbivory by these larvae to investigate whether herbivory and glucosinolate induction had an effect on oviposition preference by P. xylostella. Feeding by H. armigera and P. xylostella larvae was 2.1 and 2.5 times less, respectively, on apk1 apk2 plants (with almost no aliphatic glucosinolates) than on wild-type plants. However, there were no differences in feeding by H. armigera and P. xylostella larvae on wild-type, gsm1 (different concentrations of aliphatic glucosinolates compared to wild-type plants), and tgg1 tgg2 plants (lacking major myrosinases). Glucosinolate induction (up to twofold) as a result of herbivory occurred in some cases, depending on both the plant line and the herbivore. For H. armigera, induction, when observed, was noted mostly for indolic glucosinolates, while for P. xylostella, induction was observed in both aliphatic and indolic glucosinolates, but not in all plant lines. For H. armigera, glucosinolate induction, when observed, resulted in an increase of glucosinolate content, while for P. xylostella, induction resulted in both a decrease and an increase in glucosinolate content. Two-choice tests with wild-type and mutant plants were conducted with larvae and ovipositing moths. There were no significant differences in preference of larvae and ovipositing moths between wild-type and gsm1 mutants and between wild-type and tgg1 tgg2 mutants. However, both larvae and ovipositing moths preferred wild-type over apk1 apk2 mutants. Two-choice oviposition tests were also conducted with P. xylostella moths comparing undamaged plants to plants being attacked by larvae of either P. xylostella or H. armigera. Oviposition preference by P. xylostella was unaffected as a result of larval plant damage, even in the cases where herbivory resulted in glucosinolate induction.     

Foraging strategies of generalist and specialist Old World nectar bats in response to temporally variable floral resources

Foraging theory predicts that generalist foragers should switch resources more readily, while specialist foragers should remain constant to preferred food resources. Plant‐pollinator interactions provide a convenient system to test such predictions because floral resources are often temporally patchy, thus requiring long‐lived pollinators to switch resources seasonally. Furthermore, flowering phenologies range from ‘steady‐state’ (low‐rewarding but highly reliable) to ‘big‐bang’ (high‐rewarding but ephemeral) plant species. We assessed how nectarivorous Old World bats respond to this temporally variable floral environment by examining their diets throughout the year. Over 15 months of fieldwork in southern Thailand, we simultaneously: (1) recorded the flowering phenologies of six bat‐pollinated plant taxa; and (2) assessed the diets of seven common flower‐visiting bat species. As predicted, the generalist nectarivore (Eonycteris spelaea) frequently switched diets and utilized both big‐bang and steady‐state resources, while the specialist nectarivores (Macroglossus minimus and M. sobrinus) foraged on one or two steady‐state plant species year‐round. Our results suggest that larger and faster bat species are able to fly longer distances in search of big‐bang resources, while smaller bat species rely on highly predictable food resources. This study supports the theory that generalist foragers have flexible diets, while specialist species restrict foraging to preferred floral resources even when other floral resources are more abundant. Moreover, these findings demonstrate how plant flowering phenology and pollinator diet breadth can shape the frequency and constancy of pollinator visits; we further discuss how such interactions can influence the potential extent of gene flow within a patchy floral environment.     

Phytochemical defences and performance of specialist and generalist herbivores: a meta-analysis

1. Phytochemical coevolution theory, a long-standing paradigm in plant–insect interactions, predicts that specialist herbivores are less negatively affected by the allelochemicals of their host plants than are generalist herbivores. Although this theory is prevalent in plant–insect science, it is not always supported by empirical studies measuring the performance of specialist and generalist insects in response to allelochemicals. 2. The present study aimed to investigate: (i) whether there a difference between specialist and generalist performance in response to allelochemicals and (ii) whether the effect of allelochemicals on specialists and generalists depend upon allelochemical class or insect order. 3. A meta-analysis was conducted incorporating 76 effect sizes drawn from studies that directly compared the performance of specialist and generalist insects in response to treatment and control diets. Most of the effect sizes were related to the performance metric growth, the insect order Lepidoptera, and the allelochemical class nitrogen-containing compounds. 4. As predicted by phytochemical coevolution theory, specialist insects responded less negatively to allelochemicals of their hosts than generalist insects in terms of growth. There were no significant differences in terms of fecundity or survival, or among allelochemical classes or insect orders. 5. These results support the prediction of phytochemical coevolution theory that specialist insects respond less negatively to allelochemicals of their hosts than generalists, although only in terms of growth.     

Evolutionary rescue and the coexistence of generalist and specialist competitors: an experimental test

Competition for resources is thought to play a critical role in both the origins and maintenance of biodiversity. Although numerous laboratory evolution experiments have confirmed that competition can be a key driver of adaptive diversification, few have demonstrated its role in the maintenance of the resulting diversity. We investigate the conditions that favour the origin and maintenance of alternative generalist and specialist resource-use phenotypes within the same population. Previously, we confirmed that competition for hosts among φ6 bacteriophage in a mixed novel (non-permissive) and ancestral (permissive) host microcosm triggered the evolution of a generalist phenotype capable of infecting both hosts. However, because the newly evolved generalists tended to competitively exclude the ancestral specialists, coexistence between the two phenotypes was rare. Here, we show that reducing the relative abundance of the novel host slowed the increase in frequency of the generalist phenotype, allowing sufficient time for the specialist to further adapt to the ancestral host. This adaptation resulted in ‘evolutionary rescue’ of the specialists, preventing their competitive exclusion by the generalists. Thus, our results suggest that competition promotes both the origin and maintenance of biodiversity when it is strong enough to favour a novel resource-use phenotype, but weak enough to allow adaptation of both the novel and ancestral phenotypes to their respective niches.     

Predator–prey interactions: olfactory adaptations of generalist and specialist predators

1 Olfactory responses of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), a generalist predator, Podisus maculiventris (Say) (Hemiptera, Heteroptera: Pentatomidae) (Pm), and a specialist predator, Perillus bioculatus (F.) (Hemiptera, Heteroptera: Pentatomidae) (Pb) were investigated. Volatiles tested included 20 compounds emitted by undamaged potato plants (Solanum tuberosum), plants that had been artificially damaged, or plants damaged by feeding by CPB larvae. 2 Coupled gas chromatography/electroantennogram detector (GC/EAD) recordings revealed five compounds for which reliable responses were recorded from CPB antennae: (E)-2-hexen-1-ol, (Z)-3-hexen-1-ol, (±)-linalool, nonanal, methyl salicylate, and indole. Both Pm and Pb responded selectively to the same compounds as the CPB with exceptions: (1) (Z)-3-hexenyl butyrate elicited reliable responses for both Pm and Pb, and (2) (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol were inactive for Pm and Pb under these conditions. Dose–response curves showed that CPB was at least 100 times more sensitive to (E)-2-hexen-1-ol than were the predators. Both predators were more sensitive to each of the other compounds than were CPB. Both CPB and Pm were attracted to a five component blend comprising (E)-2-hexen-1-ol, (Z)-3-hexen-1-ol, (±)-linalool, nonanal and methyl salicylate. However, attraction of CPB to the blend occurred only with lower doses of (E)-2-hexen-1-ol and (Z)-3-hexen-1-ol. 3 These results show that the herbivore (CPB) has olfactory receptors which are more sensitive to constitutive host plant volatiles, e.g. green leaf volatiles, while both generalist (Pm) and specialist (Pb) predators are more sensitive to systemic volatiles produced in response to prey feeding. Keywords Colorado potato beetle, constitutive compounds, host plant, induced compounds, olfaction, Perillus bioculatus, Podisus maculiventris, predator, prey, tritrophic.     

Contrasting performances of generalist and specialist Myzus persicae (Hemiptera: Aphididae) reveal differential prevalence of maternal effects after host transfer

Transgenerational maternal effects on performance (rm) after host transfer were evaluated in the generalist aphid Myzus persicae s.s., and in its subspecies specialized on tobacco, M. persicae nicotianae Blackman. We tested whether the performance of these taxa, when reared separately on optimal and suboptimal hosts (as sources of different maternal background) and then transferred to optimal hosts, experienced variations along four successive generations. Additionally, to compare the tolerance of both taxa to stress following host transfers, developmental instability (fluctuating asymmetry and body abnormalities) along the four generations was assessed. Taxon, rearing host, and generation affected the performance after host transfer. In the generalist, there was a significant improvement of rm along generations when transferred from suboptimal to optimal host and a significant decrease when transferred from optimal to optimal host; in the specialist, no increase or decrease occurred in any host transfer treatment. Transfer from suboptimal to optimal hosts caused higher losses of remaining replicates along generations than transfers from optimal to optimal hosts, and the specialist showed higher losses than the generalist. The only significant effect detected in comparisons involving fluctuating asymmetry values was that of taxon on length of siphunculi. Frequency of body abnormalities was not affected by treatments. Collectively, these results show a transgenerational weakening of maternal effects in the generalist but not in the specialist aphid, and suggest that rearing the latter in a suboptimal host causes not easily reversible changes that further give rise to constraints in performance.     

Diet specialisation and foraging efficiency under fluctuating vole abundance: a comparison between generalist and specialist avian predators

Specialist species, using a narrow range of resources, are predicted to be more efficient when foraging on their preferred food than generalist species consuming a wider range of foods. We tested whether the foraging efficiency of the pallid harrier Circus macrourus, a vole specialist, and of sympatric Montagu's harriers C. pygargus, a closely related generalist, differed in relation to inter‐annual variations in vole abundance over five years (including two peak‐ one intermediate and two low vole abundance years). We show that the hunting parameters of pallid harriers strongly varied with vole abundance (higher encounter rates, capture rates and proportion of successful strikes in high than intermediate and low vole abundance years, respectively), whereas Montagu's harriers showed stable capture rates and hunting success (proportion of strikes that were successful), irrespective of vole abundance. Encounter rates and capture rates were higher for pallid than for Montagu's harriers when voles were abundant, but lower when voles were scarce. The hunting success of pallid harriers was also lower than that of Montagu's harriers when voles were scarce, and when they had to target alternative preys, in particular birds. Overall, estimated biomass intake rate was 40% higher for pallid harriers than for Montagu's harriers when voles were abundant, but 50% lower when voles were scarce. Our results indicate that specialists predators, like pallid harriers, which evolve specific adaptations or breeding strategies, do better when their preferred prey is abundant, but may face a cost of specialisation, being not efficient enough when their preferred prey is scarce. These results have broader implications for understanding why specialist predators are, in general, more vulnerable than generalists, and for predicting how specialists can cope with rapid environmental changes affecting the abundance or predictability of their preferred resources.     

Capture efficiency and trophic adaptations of a specialist and generalist predator: A comparison

Specialist true predators are expected to exhibit higher capture efficiencies for the capture of larger and dangerous prey than generalist predators due to their possession of specialized morphological and behavioral adaptations. We used an araneophagous spider (Lampona murina) and a generalist spider (Drassodes lapidosus) as phylogenetically related model species and investigated their realized and fundamental trophic niches and their efficacy with respect to prey capture and prey handling. The trophic niche of both species confirmed that Lampona had a narrow trophic niche with a predominance of spider prey (including conspecifics), while the niche of Drassodes was wide, without any preference. DNA analysis of the gut contents of Lampona spiders collected in the field revealed that spiders form a significant part of its natural diet. Lampona captured significantly larger prey than itself and the prey captured by Drassodes. As concerns hunting strategy, Lampona grasped the prey with two pairs of legs possessing scopulae, whereas Drassodes immobilized prey with silk. Lampona possess forelegs equipped with scopulae and a thicker cuticle similar to other nonrelated araneophagous spiders. Lampona fed for a longer time and extracted more nutrients than Drassodes. We show that specialized behavioral and morphological adaptations altogether increase the hunting efficiency of specialists when compared to generalists.     

Reproductive success and failure: the role of winter body mass in reproductive allocation in Norwegian moose

A life history strategy that favours somatic growth over reproduction is well known for long-lived iteroparous species, especially in unpredictable environments. Risk-sensitive female reproductive allocation can be achieved by a reduced reproductive effort at conception, or the subsequent adjustment of investment during gestation or lactation in response to unexpected environmental conditions or resource availability. We investigated the relative importance of reduced investment at conception compared with later in the reproductive cycle (i.e. prenatal, perinatal or neonatal mortality) in explaining reproductive failure in two high-density moose (Alces alces) populations in southern Norway. We followed 65 multiparous, global positioning system (GPS)-collared females throughout the reproductive cycle and focused on the role of maternal nutrition during gestation in determining reproductive success using a quasi-experimental approach to manipulate winter forage availability. Pregnancy rates in early winter were normal (≥0.8) in all years while spring calving rates ranged from 0.4 to 0.83, with prenatal mortality accounting for most of the difference. Further losses over summer reduced autumn recruitment rates to 0.23–0.69, despite negligible predation. Over-winter mass loss explained variation in both spring calving and autumn recruitment success better than absolute body mass in early or late winter. Although pregnancy was related to body mass in early winter, overall reproductive success was unrelated to pre-winter body condition. We therefore concluded that reproductive success was limited by winter nutritional conditions. However, we could not determine whether the observed reproductive allocation adjustment was a bet-hedging strategy to maximise reproduction without compromising survival or whether females were simply unable to invest more resources in their offspring.