Predation ofApochthonius minimus (Pseudoscorpionida: Chthoniidae) onFolsomia canadida (Collembola: Isotomidae)

Summary We investigated the functional response of the predaceous pseudoscorpion,Apochthonius minimus, to density of the springtail,Folsomia candida, as well as the effects of temperature and prey size on handling time and attack rate. Temperature slightly altered the overall rise in response. Both the rise and shape of the response differed for two prey sizes. The changes in number of prey eaten over a 48-hour period were also examined, and the attack and feeding behaviour ofA. minimus was described and discussed in relation to the predation experiments. The pseudoscorpion preferred young adultF. candida, 0.8–1.2 mm in length, when offered prey in the range, 0.2–1.5 mm.     

Spatial variability in seed predation in Primula farinosa: local population legacy versus patch selection

Spatio-temporal variation in seed predation may strongly influence both plant population dynamics and selection on plant traits. The intensity of seed predation may depend on a number of factors, but the relative importance of previous predator abundance (“local legacy”), spatial distribution of the host plant, environmental factors and plant characteristics has been explored in few species. We monitored seed predation in the perennial herb Primula farinosa, which is dimorphic for scape length, during 5 consecutive years, in a 10-km × 4-km area comprising 79 P. farinosa populations. A transplant experiment showed that the seed predator, the oligophagous tortricid moth Falseuncaria ruficiliana, was not dispersal limited at the spatial scale corresponding to typical distances between P. farinosa populations. Correlations between population characteristics and incidence and intensity of seed predation varied among years. The incidence of the seed predator was positively correlated with host population size and mean number of flowers, while intensity of seed predation in occupied patches was positively related to the frequency of the long-scaped morph in 2 years and negatively related to host population size in 1 year. In both scape morphs, predation tended to increase with increasing frequency of the long morph. There was no evidence of a local legacy; incidence and intensity of seed predation were not related to the abundance of the seed predator in the population in the previous year. Taken together, the results indicate that among-population variation in seed predation intensity is determined largely by patch selection and that the seed predator’s preference for tall and many-flowered inflorescences may not only affect selection on plant traits within host plant populations, but also the overall intensity of seed predation.     

Chaoborus and fish-mediated influences on Daphnia longispina population structure,dynamics and life history strategies

Summary This study examined the long term effects of predation by larvae of the midge Chaoborus and simulated fish predation on experimental Daphnia longispina populations. Chaoborus predation, relative to fish predation, led to populations composed of larger individuals as a whole, larger egg-bearing individuals, and a larger primiparous instar. Daphnia retained helmets beyond the first instar in response to the presence of Chaoborus. Both types of predation, relative to predator-free controls, reduced prey population size and rates of increase, but increased population death rates. The reduction in population size due to predation led to increased resource availability for individuals remaining in the populations and increased individual fecundity in the predation treatments. The differences noted between the Chaoborus, fish, and control treatments increased with predation intensity.     

CHAOBORUS PREDATION AND LIFE-HISTORY EVOLUTION IN DAPHNIA PULEX: TEMPORAL PATTERN OF POPULATION DIVERSITY,FITNESS, AND MEAN LIFE HISTORY

The effect of predation by the aquatic dipteran larva Chaoborus americanus on genetic diversity and life-history evolution in the cladoceran Daphnia pulex was investigated in large replicate laboratory populations. Instantaneous daily loss rates of clonal diversity and genetic variance for fitness indicate that 93–99% of initial genetic diversity can be removed from populations during the 8–12 generations of clonal reproduction that occur each year in natural populations. In the absence of predation, the principal evolved changes in mean population life history were smaller immature body size and increased and earlier fecundity. In the presence of size-selective Chaoborus predation, populations evolved toward larger body size and increased and earlier reproduction. The difference between these two trajectories is an estimate of the direct additive effect of Chaoborus predation. This effect was manifested as evolution toward larger body size with a trend toward earlier and increased reproduction.     

Predicting extinctions: interspecific competition,predation and population variability in experimental Daphnia populations

We examine how interspecific competition and two types of size-selective predation affect population density, variability and persistence in laboratory cultures of two species of Daphnia, D. magna and D. longispina. When both species were analysed together, and for D. longispina alone, there were weak negative relationships between mean population density and population variability. Interspecific competition resulted in lower population densities and higher population variability. Extinct populations had lower densities and were also more variable than persisting ones. There was still an effect of population variability on extinction probability after the effect of density on population variability had been accounted for. Hence, the effects of population density and variability on population persistence were partly independent of each other. The effects of size-selective predation on population persistence were more species-specific and not directly related to density or variability. Since the effects of species interactions on persistence were large, we suggest that it is likely that population vulnerability analyses not incorporating effects of interspecific interactions are often misleading.     

POPULATION BIOLOGY OF BONAMIA GRANDIFLORA (CONVOLVULACEAE): EFFECTS OF FIRE ON PLANT AND SEED BANK DYNAMICS

The effects of disturbance on reproduction and plant and seed bank dynamics in the perennial herb Bonamia grandiflora were studied by comparing populations in recently burned, mechanically disturbed, and undisturbed habitats in central Florida over a 3-year period. Plant densities, seed production, and the occurrence of herbivory and predispersal seed predation varied considerably between sites and between years, with recently disturbed sites supporting the densest and most dynamic populations. Death of established plants was rare in all sites. In each site, the soil seed bank was several-fold larger than single season seed rains suggesting that B. grandiflora seeds are long-lived and accumulate in the soil. There was no evidence that postdispersal predation or pathogens have any significant influence on the seed bank dynamics. Fire resulted in large increases in stem densities due to both increased clonal stem production and new genet recruitment from seed. Burning also caused significant increases in the percentage of flowers producing seed and the numbers of capsules and seeds per plant. The seed rain was ten to thirty times greater in the burned site relative to adjacent unburned site during the 3 years after burning. However, additions to the seed bank from the postfire seed rain were balanced by equivalent losses due primarily to seed mortality during fire, and to a much lesser extent due to germination and new genet establishment. As a result, the subsequent densities of seeds stored in the soil in these two sites were similar, indicating that fire results in a significant turnover in the seed bank population but no immediate change in its size. These effects on seed bank dynamics, in addition to new genet recruitment, suggest that periodic fires may play an important role in the maintenance of genetic variability as well as the size of these populations.     

Cryptic speciation in the ectocommensal Bdelloura candida (Platyhelminthes,Tricladida, Maricola) follows habitat specialization of the American horseshoe crab,Limulus polyphemus

In strict symbiotic associations, the genetic structure of the symbiont often mirrors that of its host, with interesting implications for population dynamics and phylogeography. An unresolved case of symbiotic specificity and phylogeographic consequence is the relationship between the marine triclad Bdelloura candida and its host, the American horseshoe crab, Limulus polyphemus. A recent study by Riesgo et al. (2017, Marine Biology, 164, 111) identified a strong genetic break between populations of B. candida in the Gulf of Mexico and the Atlantic Ocean but had minimal sampling around the Florida peninsula such that the exact location of the boundary zone was not specified. To solve this, a comprehensive analysis of 16S rRNA and ITS2 genetic markers was conducted from new collections around the Florida peninsula. A clear and significant genetic break was identified between populations of supposed B. candida between Cumberland Island, Georgia, and Mosquito Lagoon, Florida. This genetic break establishes two cryptic lineages, an Atlantic population as far south as Georgia and a Floridian population inclusive of the entire peninsula and Gulf of Mexico, potentially due to niche partitioning of the unique intertidal habitats of its horseshoe crab hosts in Florida. This result directly refutes the previous hypothesis that a population break exists between the coasts of the Atlantic Ocean and Gulf of Mexico, and instead matches the genetic break of its host. Furthermore, a third cryptic lineage was identified in Key West. Overall, this work demonstrates the challenges in maintaining genetic connections between populations of both B. candida and L. polyphemus across their distributions, and poses meaningful implications for both species in the larger context of marine conservation and biodiversity.     

Impact of Cheiracanthium pelasgicum (Araneae: Miturgidae) and Chrysoperla carnea (Neuroptera: Chrysopidae) intraguild predation on the potential control of cotton pest Helicoverpa armigera (Lepidoptera: Noctuidae)

Antagonist interactions such as intraguild predation (IGP) or cannibalism among predatory arthropods can reduce the impact of these invertebrates on pest limitation in agroecosystems. Here, the effects of IGP between two major natural enemies of cotton pests, the cursorial spider Cheiracanthium pelasgicum (C.L. Koch) and the common green lacewing Chrysoperla carnea (Stephens), were studied under laboratory conditions. First, a feeding preference test was carried out to determine the degree of C. pelasgicum preference for lacewing larvae, using second-instar Helicoverpa armigera larvae as alternative prey. In a second bioassay, the effects of predator interactions on potential predation of H. armigera larvae were analysed using three treatment combinations (plus a control with no predator): (1) spider alone, (2) lacewing larvae alone, (3) spider + lacewing larvae. Potential predation by C. pelasgicum on lacewing eggs was also studied. C. pelasgicum showed no significant preference for either of the two species, indicating that this spider may impact negatively on the green lacewing population. Findings revealed no additive effects and an antagonist interaction between C. pelasgicum and green lacewing larvae, which adversely affected H. armigera suppression; both predators displayed lower predation rates when kept together than either predator alone. However, presence of lacewing larvae and subsequent unidirectional IGP did not affect the predation capacity of C. pelasgicum. Finally, predation rates of C. pelasgicum on lacewing eggs were very low (mean 2.35 ± 0.71 eggs, 24 h after offering) indicating that the impact of C. pelasgicum on lacewing populations may be limited.     

Can redistribution of breeding colonies on a landscape mitigate changing predation danger?

The reproductive success of colonially breeding species depends in part upon a trade‐off between the benefit of a dilution effect against nestling predation within larger colonies and colony conspicuousness. However, there may be no net survivorship benefit of dilution if smaller colonies are sufficiently inconspicuous. This raises the question about how the size distribution of breeding colonies on a landscape might change as the predation danger for nestlings changes. In southwest British Columbia, Canada, bald eagle Haliaeetus leucocephalus populations have increased exponentially at ～5% per year in recent decades and prey upon nestlings of colonial breeding great blue herons Ardea herodias faninni. Motivated by field data on reproductive success in relation to colony size, modeling is used to ask under which circumstances trading off a dilution benefit against colony conspicuousness can improve population reproductive success. That is, which colonial nesting distribution, dispersed and cryptic versus clumped and conspicuous, best mitigates predation danger on nestlings? When predators are territorial, the modeling predicts a dispersed nesting strategy as attack rate increases, but not as predator numbers increase. When predators are non‐territorial, the modeling predicts a dispersed nesting strategy as predator numbers and/or attack rates increase. When predators are both territorial and non‐territorial, colonial nesting within a predator's territory improves reproductive success when attack rates are low. This suggests nesting in association with territorial predators may offer decreased levels of predation when compared with nesting amongst non‐territorial predators. Thus a change in the colony size distribution of colonially breeding species might be anticipated on a landscape experiencing a change in predation danger.     

Comparative population structure of three snook species (Teleostei: Centropomidae) from the eastern central Pacific

Three snook species, Centropomus viridis, Centropomus medius, and Centropomus robalito, from the eastern central Pacific, representing three of the four proposed phyletic lineages in the genus, were analyzed for genetic variability by means of allozyme and RAPD to evaluate the divergence between populations at different levels of dispersal ability and to evaluate the importance of barriers to dispersal in the population subdivision and genetic diversity. Levels of genetic diversity among species estimated by allozymes were similar and consistent with the observed levels of differentiation in marine fish species. Mean heterozygosity ranged from 0.089 for C. viridis to 0.10 for C. robalito. Genetic diversity for the snook species studied was slightly higher than the mean estimation reported in allozymes for 106 marine fish (0.055) and for anadromous fish species (0.043 to 0.057). Multilocus allele frequency homogeneity tests and population-subdivision estimates for both allozyme and RAPD markers revealed the existence of population structure in C. viridis and C. medius, in coincidence with geographic separation of samples, whereas no divergence was detected in C. robalito. This finding may be attributed to the greater population size of C. robalito, which originated by a recent population range expansion, and hence the potential for dispersal is mediated by larval drift. Fluctuations in population size and population range expansion are used to explain discrepancies between levels of genetic diversity and population structure in the studied species. Supplementary material to this paper is available in electronic format at     

Accidental altruism in insular pit-vipers (Gloydius shedaoensis, Viperidae)

Darwinian theory predicts that organisms will display traits that benefit themselves rather than other individuals; exceptions to this rule usually are explicable by kin selection. Our studies on an insular population of venomous snakes in north-eastern China reveal a different situation. Only one species of snake (Gloydius shedaoensis, Viperidae) occurs on the island of Shedao, and displays altruism between size (age) classes. First, small snakes frequently kill prey items larger than they can swallow themselves. This behaviour enhances rates of feeding of larger conspecifics, which scavenge the birds' carcasses. Second, large snakes kill raptorial birds (sparrowhawks Accipiter nisus) that pose little or no threat to themselves. This behaviour reduces predation risk for smaller snakes. These effects are presumably accidental consequences of the high venom toxicity of the pit-vipers, which enable them to kill inedible prey and non-threatening predators at little cost. Nonetheless, this accidental altruism may have significant ecological consequences. For example, these behaviours may contribute to the remarkably high population densities of snakes on Shedao.     

PHENOTYPIC DIVERSIFICATION ACROSS AN ENVIRONMENTAL GRADIENT: A ROLE FOR PREDATORS AND RESOURCE AVAILABILITY ON THE EVOLUTION OF LIFE HISTORIES

Changes in age/size‐specific mortality, due to such factors as predation, have potent evolutionary consequences. However, interactions with predators commonly impact prey growth rates and food availability and such indirect effects may also influence evolutionary change. We evaluated life‐history differences in Trinidadian killifish, Rivulus hartii, across a gradient in predation. Rivulus are located in (1) “high predation” sites with large piscivores, (2) “Rivulus/guppy” sites with guppies, and (3) “Rivulus‐only” sites with just Rivulus. Rivulus suffer higher mortality with large predators, and guppies may prey upon small/young Rivulus in Rivulus/guppy environments. In turn, population densities decline while growth rates increase in both localities compared to Rivulus‐only sites. To explore how the direct and indirect effects of predators and guppies influence trait diversification in Rivulus, we examined life‐history phenotypes across five rivers. High predation phenotypes exhibited a smaller size at reproduction, a greater number of eggs that were smaller, and increased reproductive allotment. Such changes are consistent with a direct response to predation. Rivulus from Rivulus/guppy sites were intermediate; they exhibited a smaller size at reproduction, increased fecundity, smaller eggs, and larger reproductive allotment than Rivulus‐only fish. These changes are consistent with models that incorporate the impacts of growth and resources.     

Genetics of Brazil nut (Bertholletia excelsa Humb. & Bonpl.: Lecythidaceae)

Summary We provide an estimate of genetic variation within and between two populations of Bertholletia excelsa (Brazil nut), a large canopy tree found in the rain forests of South America. Average heterozygosity is 0.190, and 54.3% of the sampled loci are polymorphic. The population structure deviates significantly from Hardy-Weinberg expectations for Fest2 and Pgm2 (F =0.405 and 0.443, respectively) in one population, and highly significantly (F=-0.341) for Gdh in the other population. Although allele frequencies of the two populations differ significantly for Aat2, Est5, Mdh1, and Mdh2B, Nei's coefficient of gene differentiation (G_st) indicates that the between-population component (D_st) of genic diversity represents only 3.75% of the size of the within-population component (H_s). The implications of these findings in terms of conservation genetics are that much of the genetic diversity of this species may be preserved within one or a few populations. However, such populations must be very large because it appears that the large amount of genetic variation in Brazil nut populations is maintained by extensive gene flow and bonds of mating over a large area. The genetic architecture of Bertholletia excelsa is similar to that expected for an extensively diploidized paleopolyploid species.     

Spatial and temporal dynamics of the male effective population size in bumblebees (Hymenoptera: Apidae)

Eusociality and male haploidy of bumblebees (Bombus spp.) enhance the deleterious effects of population decline and aggravate the degeneration of population fitness compared to solitary and diploid species. The highly dispersive male sex may be the prime driver to connect otherwise isolated populations. We therefore studied the temporal and spatial structure of the male population of Bombus terrestris (Linnaeus 1758) and Bombus lapidarius (Linnaeus 1758) using microsatellite DNA markers. We found that the majority of the males in a 1000 m2 sampling area originated from colonies located outside of the workers foraging range, which was consistent with the genetic distances among colonies. The analyses of temporal population sub-structure based on both colony detection rate over time and the clustering software STRUCTURE consistently suggested one large and temporally unstructured male population. Our results indicate an extended male flight distance for both species. Though the range of queen dispersal remains to be studied, the effective size (N _e) of bumblebees is increased by extended male mating flight ranges (A _m ) exceeding worker foraging distance by factor 1.66 (A _m  = 69.75 km²) and 1.74 (A _m  = 13.41 km²), B. terrestris and B. lapidarius, respectively. Thus this behaviour may counteract genetic deprivation and its effects. All populations were genetically highly diverse and showed no signs of inbreeding. We discuss the implications of our findings in context of bumblebee population dynamics and conservation. We also highlight the effects and benefits of sampling both workers and males for population genetic studies.     

Impact of predation by the robber fly Proctacanthus milbertii (Diptera: Asilidae) on grasshopper (Orthoptera: Acrididae) populations

The impact of predation by the robber fly Proctacanthus milbertii Macquart on populations of adult grasshoppers from grasslands of the Nebraska sandhills was estimated. Densities of P. milbertii were estimated at 437 individuals per hectare (2 se=122). Overall densities of 23 species of grasshoppers were estimated to be 64,000 individuals per hectare with the most abundant species (Ageneotettix deorum) having a population size of approximately 15,000 individuals per hectare. Based on three estimates of predation level (ranging from 0.5 to 2 prey per day per robber fly), P. milbertii may take from 0.5% to 2% of the adult grasshoppers per day. Species of grasshoppers were taken by P. milbertii in about the same proportion in which they occurred at the study site and no size-selective component of predation was detectable.     

Butterfly seed predation: effects of landscape characteristics,plant ploidy level and population structure

Polyploidization has been suggested as one of the most common mechanisms for plant diversification. It is often associated with changes in several morphological, phenological and ecological plant traits, and therefore has the potential to alter insect–plant interactions. Nevertheless, studies evaluating the effect of plant polyploidy on interspecific interactions are still few. We investigated pre-dispersal seed predation by the butterfly Anthocharis cardamines in 195 populations of two ploidy levels of the herb Cardamine pratensis (tetraploid ssp. pratensis, 2n = 30 vs. octoploid ssp. paludosa, 2n = 56–64). We asked if differences in incidence and intensity of predation among populations were related to landscape characteristics, plant ploidy level and population structure. The incidence of the seed predator increased with increasing plant population size and decreasing distance to nearest population occupied by A. cardamines. The intensity of predation decreased with increasing plant population size and was not affected by isolation. Probability of attack decreased with increasing shading, and intensity of predation was higher in grazed than in non-grazed habitats. The attack intensity increased with increasing mean flower number of plant population, but was not affected by flowering phenology. Individuals in tetraploid populations suffered on average from higher levels of seed predation, had higher mean flower number, were less shaded and occurred more often in grazed habitats than octoploid populations. When accounting for differences in habitat preferences between ploidy levels there was no longer a difference in intensity of predation, suggesting that the observed differences in attack rates among populations of the two ploidy levels are mediated by the habitat. Overall, our results suggest that polyploidization is associated with differentiation in habitat preferences and phenotypic traits leading to differences in interspecific interaction among plant populations. This, in turn, may facilitate further divergence of ploidy levels.     

Geographic variation in offspring size of a widespread lizard (Takydromus septentrionalis): importance of maternal investment

Geographic variation in offspring size is widespread, but the proximate causes of this variation have not yet been explicitly determined. We compared egg size and egg contents among five populations of a lizard (Takydromus septentrionalis, Günther, 1864) along a latitudinal gradient, and incubated eggs at two temperatures to determine the influence of maternal investment and incubation temperature on offspring size. The mean values for female size and egg size were both greater in the two northern populations (Chuzhou and Anji) than in the three southern populations (Lishui, Dongtou, and Ningde). The larger eggs were entirely attributable to the body size of females in the Anji population, but their increased size also stemmed from further enlargement of egg size relative to female body size in Chuzhou, the northernmost population sampled in this study. Eggs of the Chuzhou population contained more yolk and less water than those of southern populations. Despite the lower lipid content in the yolk, eggs from the Chuzhou population had higher energy contents than those from the two southern populations, owing to the larger egg size and increased volume of yolk. Hatchling size was not affected by incubation temperature, but differed significantly among populations, with hatchlings being larger in the Chuzhou population than in the other populations. Our data provide an inference that oviparous reptiles from cold climates may produce larger offspring, not only by increasing egg size but also by investing more energy into their eggs. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 59–67.     

Ontogenetic Behaviour Changes in Larvae of the Damselfly Ischnura verticalis (Odonata: Coenagrionidae)

Larvae of most animals go through large changes in size. Because change in size can lead to changes in ability to gain food and in predation risk, changes in behaviour are predicted to reflect this. Models consider change in amounts of the same behaviour, but different selective pressures on different larval sizes may also lead to qualitative differences in behavioural repertoire. In the damselfly Ischnura verticalis we observed ontogenetic changes in behaviour under controlled laboratory conditions. We found that frequency and duration of feeding behaviour and behaviour related to activity were increased in larger instars. Larger larvae also had higher transition probabilities to the behaviour abdomen wave, straight abdomen raise, and rotate + head out. We also found that the behavioural repertoire of damselfly larvae changed with development: some behavioural patterns were performed almost exclusively by smaller larvae (F - 4 to F - 7) while others were performed almost exclusively by larger larvae (F - 3 to F - 0).     

Forest fragmentation and plant reproductive success: a case study in four perennial herbs

We assessed the effects of habitat fragmentation on reproductive success in natural populations of four forest herbs with differing life-history traits and whose distribution patterns appeared to be negatively affected by decreased habitat size and/or increased isolation: Carex sylvatica, Galium odoratum, Sanicula europaea and Veronica montana. Our aims were to test (1) whether habitat size and isolation are positively correlated with population size and isolation, respectively, (2) whether plant reproductive success, a major component of plant fitness, is reduced in small and/or isolated populations when also accounting for differences in habitat quality (edaphic conditions, light intensity) and the effects of plant size, and (3) whether species with different life histories are affected differently. There were significant positive relationships between habitat and population size and between habitat and population isolation in some, but not all of the species. We mostly found no negative effects of small population size or isolation on reproduction. However, reproductive success was reduced in small populations of Sanicula, and this effect was independent of differences in plant size and environmental conditions. The reduced fecundity in small populations may be a consequence of the Allee-effect, a possible mechanism being pollen limitation. Furthermore, the proportion of flowering ramets was reduced in small and isolated populations of Galium, which may have been caused by changes in population structure. Lastly, we found some evidence for largely outcrossing, non-clonal species to be more sensitive to reductions in population size, at least in terms of their reproductive success.     

Habitat-specific size structure variations in periwinkle populations (<Emphasis Type="Italic">Littorina littorea)</Emphasis> caused by biotic factors

Shell size distribution patterns of marine gastropod populations may vary considerably across different environments. We investigated the size and density structure of genetically continuous periwinkle populations (Littorina littorea) on an exposed rocky and a sheltered sedimentary environment on two nearby islands in the south-eastern North Sea (German Bight). On the sedimentary shore, periwinkle density (917 ± 722 individuals m⁻²) was about three times higher than on the rocky shore (296 ± 168 individuals m⁻²). Mean (9.8 ± 3.9 mm) and maximum (22 mm) shell size of L. littorea on the sedimentary shore were smaller than on the rocky shore (21.5 ± 4.2 and 32 mm, respectively), where only few small snails were found. Additionally, periwinkle shells were thicker and stronger on the rocky than on the sedimentary shore. To ascertain mechanisms responsible for differences in population structures, we examined periwinkles in both environments for growth rate, predation pressure, infection with a shell boring polychaete (Polydora ciliata) and parasitic infestation by trematodes. A crosswise transplantation experiment revealed better growth conditions on the sedimentary than on the rocky shore. However, crab abundance and prevalence of parasites and P. ciliata in adult snails were higher on the sedimentary shore. Previous investigations showed that crabs prefer large periwinkles infested with P. ciliata. Thus, we suggest that parasites and shell boring P. ciliata in conjunction with an increased crab predation pressure are responsible for low abundances of large periwinkles on the sedimentary shore while high wave exposure may explain low densities of juvenile L. littorea on the rocky shore. We conclude that biotic factors may strongly contribute to observed differences in size structure of the L. littorea populations studied on rocky and sedimentary shores.