Estimating population characteristics of two saproxylic beetles: a mark-recapture approach

Using a mark-release-recapture technique we describe adult sex ratios, recapture rates and other sample characteristics of two saproxylic species: the nationally threatened longhorn beetle Leptura (Rutpela) maculata (Coleoptera: Cerambycidae) and the common L. quadrifasciata in southeastern Finland over two summers. Over 350 individuals of L. maculata and 150 individuals of L. quadrifasciata were captured on floral resource or in flight, and marked each summer. For L. maculata, the sex ratio was male-biased (2:1), whereas for L. quadrifasciata the bias was less clear. For both species, the male-bias may reflect behavioral differences between sexes, rather than true population differences. The proportion of recaptured individuals was low and varied between 7 and 33% depending on the species and year, which allowed us to estimate population parameters only for L. maculata in 2006. A model which assumed constant survival, but time-dependent catchability and entrance probability from a larger superpopulation, fit the data best. The precision of the total population size estimates were reasonable for all the models tested (coefficient of variation = 7–14%). Based on the estimated local adult population size (mean ± 95% confidence interval = 865 ± 131), and the current distribution area of L. maculata, we infer that the species is not in immediate risk of extinction in Finland. Our analysis shows that mark-recapture technique can provide precise estimates of adult population size of saproxylic beetles which have different adult and larval habitats, and thus be useful in assessing extinction risk and monitoring population trends.     

Empirical estimates of historical variations in the catchability and fishing power of pelagic longline fishing gear

I quantify the effects of 11 variables on the catchability and fishing power of pelagic longlines, which are used to catch tunas and billfishes in the open ocean. Extension of the depth range and the duration of longline operations have reduced the catchability of several epipelagic species, such as mako sharks (Isurus spp.), since industrial longlining commenced in the tropical Pacific Ocean in the early 1950s. Reductions in the body size of many species may also have reduced encounters with longline hooks. By contrast, the catchability of commercially valuable bigeye tuna (Thunnus obesus) increased substantially because of the longer duration and extension of the depth range of longlines. Stronger and less visible line materials and increased fishing-master experience also contributed to increased catchability. By affecting the rate of bait loss, the introduction of new bait species increased fishing power. This study highlights significant problems in deriving indices of abundance from commercial catch and effort data. Instead of relying on commercial data, assessments should use tag-recapture experiments or dedicated surveys to obtain fishery-independent estimates of abundance.     

Male-biased sex ratios in mature damselfly populations: real or artefact?

1. There is ongoing controversy about whether biased sex ratios in diploid insect populations are real or an artefact caused by different behaviours and/or different catchability of the sexes. This was tested by monitoring two field and three semi-natural populations of the damselfly Lestes sponsa. 2. Capture–mark–recapture data showed that population size estimates were about twice as large for males as for females at both field sites. Independent estimates of the sex ratios based on total numbers of males and females captured supported the male bias. 3. Males had higher recapture probabilities than females due to longer times between successive visits in females. Because the same pattern was found in the semi-natural populations, the longer intervals in females are no artefact due to their lower detectability. 4. Theoretical models show that the strong temporary emigration of females tends, if anything, to overestimate female population sizes and that the heterogeneity of recapture probabilities observed in males tends to underestimate male population sizes. Hence, behavioural differences between the sexes do not cause an artificially male-biased sex ratio. 5. Spatial data show that operational sex ratios are male biased at the pond but become female biased in the plots further away from the shoreline; however because of the decrease in densities away from the shoreline, this does not result in a global even sex ratio. 6. Spatial data, temporary emigration patterns, and independent estimates suggest strongly that the male-biased sex ratios in mature damselfly populations are real.     

A Hierarchical Model to Estimate Fish Abundance in Alpine Streams by using Removal Sampling Data from Multiple Locations

The author compares 12 hierarchical models in the aim of estimating the abundance of fish in alpine streams by using removal sampling data collected at multiple locations. The most expanded model accounts for (i) variability of the abundance among locations, (ii) variability of the catchability among locations, and (iii) residual variability of the catchability among fish. Eleven model reductions are considered depending which variability is included in the model. The more restrictive model considers none of the aforementioned variabilities. Computations of the latter model can be achieved by using the algorithm presented by Carle and Strub (Biometrics 1978, 34 , 621–630). Maximum a posteriori and interval estimates of the parameters as well as the Akaike and the Bayesian information criterions of model fit are computed by using samples simulated by a Markov chain Monte Carlo method. The models are compared by using a trout (Salmo trutta fario) parr (0+) removal sampling data set collected at three locations in the Pyrénées mountain range (Haute‐Garonne, France) in July 2006. Results suggest that, in this case study, variability of the catchability is not significant, either among fish or locations. Variability of the abundance among locations is significant. 95% interval estimates of the abundances at the three locations are [0.15, 0.24], [0.26, 0.36], and [0.45, 0.58] parrs per m². Such differences are likely the consequence of habitat variability.     

A comparison of the reproductive cycles of Modiolus modiolus (L.), Cerastoderma (=Cardium) edule (L.), and Mytilus edulis L. in Strangford Lough,Northern Ireland

Summary This paper examines the reproductive cycles of three ecologically important marine bivalves-Modiolus modiolus (L.), Cerastoderma edule (L.), and Mytilus edulis L. in Strangford Lough, Northern Ireland over a period of almost five years.Whilst Modiolus does not appear to become sexually mature until it is several years old, Mytilus and Cerastoderma can reproduce in their first and second years of life respectively. In Cerastoderma and Modiolus sexual maturity is preceded by a period of rapid somatic growth.The subtidal Modiolus population remained in a more or less fully ripe condition virtually throughout the period of this investigation suggesting that this particular population lacked any marked cyclical reproductive activity. We interpret this as evidence of slow but almost continuous release of gametes throughout much of the year, a suggestion which is supported by recruitment data. A small intertidal population of Modiolus in Belfast Lough monitored over a period of two years exhibited a much more seasonal cycle. Here spawning occurred mainly during the autumn and winter. These data suggest that localised environmental factors are exceedingly important in controlling the annual reproductive cycle of this species. Cerastoderma from the mid-tidal sand flats ripened rapidly during the spring and spawned over a relatively restricted period in the summer. In Strangford Lough Mytilus occurs predominantly in the low-shore and while it spawns mainly in the spring and summer the annual cycle is considerably more protracted and variable than in Cerastoderma.Variations in the duration of the spawning periods in these bivalves can perhaps be explained in terms of both environmental stability and the immediate physical conditions experienced by these particular populations. The reproductive strategies exhibited by Cerastoderma, Modiolus, and Mytilus in Strangford Lough are considered in relation to population stability and to the different patterns of mortality which characterise these species in their respective local habitats.     

Catchability: a key parameter for fish stock assessment

Summary Catchability is a concept in fishery biology which reflects the efficiency of a particular fishery. Its quantitative magnitude is expressed by the catchability coefficient, which relates the biomass abundance to the capture or fishing mortality. This paper is a comprehensive review of catchability including the development of our knowledge, interpretation and estimation.Catchability patterns indicate that the catchability coefficient has been used in two main lines: (a) increased efficiency of fishing effort and (b) its relation to population fishery processes for assessment and management purposes. It involves various aspects of the fishery, such as individual and population biology, characteristics of the fishing gear, amount of fishing, fishing strategies, and environmental fluctuation, among others.The concept is proposed of an integrated model of the catchability coefficient, which incorporates various of the aspects mentioned above. It is illustrated with two examples of its application: the red grouper (Epinephelus morio) fishery from the Campeche Bank, Gulf of Mexico, and the sardine (Sardinops caeruleus) fishery from the Gulf of California.     

Accuracy of catch-effort methods for estimating fish density and biomass in streams

Synopsis At each of 11 localities a section of stream was closed off with nets and an electrofisher used to estimate the abundance of fishes in the section. Each section was fished from 5–7 times with each fishing equalling one unit of effort. Using the catch-effort methods of Leslie, DeLury and Ricker, separate estimates were made for each species. In several cases species were split into size groups and estimates made for each group. The fish remaining in each section after the fishings were collected using rotenone. Thus the estimates could be compared to the actual number of fish present. Estimates were considered to be either good, if the regressions used in the above methods were statistically significant or bad if they were not significant. Lower limits for the number of fish and mean weight of a fish for good estimates were identified.The Leslie and Ricker estimates, which did not differ significantly, were least in error. They tended to underestimate (–21.6% on the average for the Leslie method). Direct estimates of biomass did not differ significantly from those made using the estimates for numbers and the mean weight of fish caught. The interrelationships among variables such as mean weight, numbers, catchability, density, biomass, number of catches used, proportion of fish taken during the estimate, number of fish in the last catch and their relationships with the error of the estimates were examined using correlation and principal components analysis. Error was most closely related to the proportion of fish collected. The effects of other variables such as mean weight affected error through catchability and subsequently the proportion of fishes caught. It was not possible to predict a significant proportion of the error using variables which could be measured without a complete collection. The effects of locality, electrofisher, and species on error were examined. Each accounted for a significant proportion of the variability in error but primarily by affecting the proportion of fish caught.These results suggest that the most appropriate way of decreasing error would be to increase the total effort and consequently the proportion of fish collected. This would be best done by increasing the number of fishings used in the estimate.Catchability tended to decrease in successive fishings. The observed trends in changing catchability accounted for most of the error. Size-selectivity, which was evident as a change in mean weight in successive catches, was not significantly associated with changing catchability.     

Unequal catchability of male Bufo bufo within breeding populations

For 9 years, three breeding populations of the common toad Bufo bufo were censused during the breeding season. The hypothesis that catchability is equal for breeding males in each population and breeding period was tested. By comparing the lengths of all males captured with those recaptured in the same breeding period, it was shown that large males had a higher catchability than small ones. The ultimate cause of this unequal catchability remains unclear, but several causes can be rejected. Population parameters based on capture and capture – recapture data are highly influenced by this unequal catchability.     

Genetic structure of European and Mediterranean maize borer populations on several wild and cultivated host plants

Target pests may become resistant to Bacillus thuringiensis (Bt) toxins produced by trangenic maize (Zea mays L.). Untreated refuge areas are set aside to conserve high frequencies of susceptibility alleles: a delay in resistance evolution is expected if susceptible individuals from refuges mate randomly with resistant individuals from Bt fields. In principle, refuges can be toxin‐free maize or any other plant, provided it hosts sufficiently large pest populations mating randomly with populations from Bt‐maize fields. Our aim was to examine the suitability of several cultivated or weedy plants [pepper (Capsicum frutescens L.), sorghum (Sorghum spec.), sunflower (Helianthus annuus L.), cocklebur (Xanthium spec.), cantaloupe (Cucumis melo L.), and hop (Humulus lupulus L.)] as refuges for Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) and Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae), two major maize pests in southern Europe. Larvae of both species were collected on these plants. Their genetic population structure was examined at several allozyme loci. We found little or no evidence for an influence of geographic distance, but detected a significant host‐plant effect on the genetic differentiation for both species. Ostrinia nubilalis populations from sunflower, pepper, cocklebur, and sorghum appear to belong to the same genetic entity as populations collected on maize, but to differ from populations on hop. Accordingly, females from pepper and cocklebur produced exclusively the ‘Z’ type sexual pheromone, which, in France, characterizes populations developing on maize. Qualitatively, these plants (except hop) could thus serve as refuges for O. nubilalis; however, they may be of little use quantitatively as they were found much less infested than maize. Sesamia nonagrioides populations on maize and sorghum reached comparable densities, but a slight genetic differentiation was detected between both. The degree of assortative mating between populations feeding on both hosts must therefore be assessed before sorghum can be considered as a suitable refuge for this species.     

A field study of the effect of prebaiting on censusing by the capture-recapture method in a vole population

Populations of the vole, Clethrionomys rufocanus, in a lowland woodlot of Hokkaido were studied for the presence of effects of prebaiting on censusing by the capture-recapture method. A grid of 121 live-traps, spaced 5 m apart, was laid out on each of two plots, one of which alone was prebaited three days long. Owing to very high densities and great trap-efficiency, sufficient and favourable samples could be available for statistical analysis, except the trend of delayed catch for young in sampling. The population on either plot, however, proved to be markedly variable in catchability of unmarked animals in the course of trapping; while the probability of recapture was counted as invariable on the average from day to day, the recapture frequency was different between juveniles, subadults and adults. Needless to say, the catchability was distinctly greater for marked voles than for unmarked ones, whether prebaited or not, through the trapping period, except that the first-day catchability for unmarked ones on the prebaited plot seems not to be significantly lower than that for marked ones. Consequently, it turns out that the prebaiting has almost never helped to eliminate the important bias induced by differential trap-response of marked and unmarked animals; its contribution is only that the catchability for unmarked ones is slightly higher on the part of the prebaited plot on earlier days of the period. In accordance with the heterogeneous catchability, the Γ-form distribution analogous to the geometric could be applied with thorough fitness to the capture frequency in order to estimate the whole populations. The fact that the estimates are reliable, being not at any rate underestimates, was further confirmed by the result of a follow-up work conducted by means of the removal method with wider trap-spacing which brought forth distinct underestimation chiefly referable to unexposure to traps of the partial populations. The subject of unexposure was discussed by laying stress on the relation between minimum range length and trap-spacing.     

Performance of leaf beetle larvae on sympatric host and non-host plants

Studies asking the ability of insects to utilize novel host plants often use novel hosts that are allopatric with the insect population under investigation. However, since the outcomes of species interactions are often site-specific, such studies cannot tell us whether a plant would actually be used by a given insect population if the plant grew sympatrically with it. We therefore performed a quantitative genetics experiment to analyse the performance of larvae of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae, Chrysomelinae) on two host and three non-host plants, collected from a site where insects and plants co-occur in the Western Alps. When raised on the non-host Petasites albus (L.), larvae were able to survive equally well as on the two hosts, Adenostyles alliariae (Gouan) and Cirsium spinosissimum (L.), whereas they did not survive on the two other non-hosts, Peucedanum ostruthium (L.) and Rumex alpinus L. On P. albus, growth rate was slightly lower and development time slightly longer than on the two hosts. We found a genotype by environment interaction only for growth rate but not for development time and survival. However, the shape of the reaction norms of growth rates suggests that it is unlikely that selection could favour the inclusion of P. albus into the host range of the study population.     

Marker‐based estimates of relatedness and inbreeding coefficients: an assessment of current methods

Inbreeding (F) of and relatedness (r) between individuals are now routinely calculated from marker data in studies in the fields of quantitative genetics, conservation genetics, forensics, evolution and ecology. Although definable in terms of either correlation coefficient or probability of identity by descent (IBD) relative to a reference, they are better interpreted as correlations in marker‐based analyses because the reference in practice is frequently the current sample or population whose F and r are being estimated. In such situations, negative estimates have a biological meaning, a substantial proportion of the estimates are expected to be negative, and the average estimates are close to zero for r and equivalent to F_IS for F. I show that although current r estimators were developed from the IBD‐based concept of relatedness, some of them conform to the correlation‐based concept of relatedness and some do not. The latter estimators can be modified, however, so that they estimate r as a correlation coefficient. I also show that F and r estimates can be misleading and become biased and marker dependent when a sample containing a high proportion of highly inbred and/or closely related individuals is used as reference. In analyses depending on the comparison between r (or F) estimates and a priori values expected under ideal conditions (e.g. for identifying genealogical relationship), the estimators should be used with caution.     

Allelopathy and the allelothathic activity of a phenylpropanol from cucumber plants

The growth inhibitory effect of cucumber (Cucumis sativus L.) plants after crop harvested was investigated. Aqueous methanol extracts of the cucumber plants inhibited the growth of roots and shoots of cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.), ryegrass (Lolium multiflorum L.), timothy (Pheleum pratense L.), crabgrass (Digitaria sanguinalis L.), Echinochloa crus-galli (L.) Beauv and Echinochloa colonum (L.) Link, and increasing the extract concentration increased the inhibition. These results suggest that cucumber plants may possess allelopathic activity. The aqueous methanol extract of cucumber plants was divided into ethyl acetate and aqueous fractions, and the growth inhibitory activity of ethyl acetate fraction was greater than that of aqueous fraction. Thus, ethyl acetate fraction was further purified and a main allopathically active substance in the fraction was isolated and determined as (S)-2-benzoyloxy-3-phenyl-1-propanol by spectral data. This substance inhibited root and shoot growth of cress seedlings at concentrations greater than 10 μM, and the concentration required for 50% inhibition of root and shoot growth was 21 and 23 μM, respectively. These results suggest that (S)-2-benzoyloxy-3-phenyl-1-propanol may contribute to the growth inhibitory effect of cucumber plants and may play an important role in cucumber allelopathy. Thus, cucumber plants may be potentially useful for weed management in a field setting. An erratum to this article can be found at     

Field manipulation of populations of individual staphylinid species in cereals and their impact on aphid populations

Abstract.

• 1 Four species of staphylinids were caged separately on wheat and their effect on the population development of the grain aphid, Sitobion avenae (F.), was investigated over two seasons.
• 2 A novel field cage design was used to exclude all but the staphylinid species under investigation.
• 3 Predator effects were compared with total-exclusion cages in which all predators and parasitoids were kept out.
• 4 During a high-density phase of aphid population development only Philonthus cognutus (Stephens) significantly influenced aphid population numbers.
• 5 At low aphid densities, Tachyporus obtusus (L.), T.chrysomelinus (L.) and P.cognatus reduced aphid population levels.
• 6 The experiments showed that Tachyporus spp. can reduce the numbers of cereal aphids prior to the exponential phase of aphid population increase and that P.cognatus causes some reduction at both the stages of aphid population growth investigated.

     

Photosynthate partitioning into leaf starch as affected by daily photosynthetic period duration in six species

Starch accumulation rates increased up to five-fold in the leaves of five out of six species examined when plants were shifted from a long (12 or 14-h) to a short (7-h) photosynthetic period. The five species that responded were corn (Zea mays L.), pangola (Digitaria decumbens Stent.), soybean (Glycine max L.) Merr.), spinach (Spinacia oleracea L.), and sugarbeet (Beet vulgaris L.) However, the rate of starch accumulation in alfalfa (Medicago sativa L.) was unaltered following a shift from a long to a short photosynthetic period. We conclude that photosynthate partitioning into chloroplast starch, at least in a wide variety of species, is a programmable process that can be manipulated by altering the length of the daily photosynthetic period.     

Accurate and efficient estimation of benthic populations: A comparison between removal estimation and conventional sampling techniques

A Circular Depletion Sampler (CDS) was designed to allow the removal of consecutive subsamples from a sample area, while minimizing immigration and emigration. Equal sampling effort was expended during each removal period to permit estimation of both the probability of capture, and the number of individuals not captured from a sample area. Average probabilities of capture from 270 CDS samples ranged from 0.19 per minute for Antocha (Tipulidae) to 0.96 for Paratendipes (Chiroal (3 removal periods), Surber, and kick-net methods. Removal population estimates were consistently higher and less variable than those of the other methods. Estimates of diversity from samples taken with conventional methods were biased by differences in catchability, and by emigration. Separation of benthos from detritus took about twice as long per unit sample area for Surber and kick-net methods, although sampling time per unit area was nearly equal for all three methods. Removal estimates using only the first two catches were comparable to estimates based on three catches, indicating a further possible increase in efficiency.     

Comparative sequencing of a microsatellite locus reveals size homoplasy within and between european oak species (<Emphasis Type="Italic">Quercus</Emphasis> spp.)

Microsatellites (simple sequence repeats [SSRs]) are highly variable molecular markers that are a rich and readily assayed source of variation for population genetic studies. Cross-amplification between closely related species is possible when there are no (or few) sequence differences in the primer binding sites. The occurrence of nonhomologous fragments of the same size (size homoplasy) is a contraint of microsatellites. Size homoplasy can be caused by insertions/deletions (indels) in SSR flanking regions. We found that size variation in locus ssrQZAG9 is due to different repeat numbers of the SSR motifs but also to indels in SSR flanking regions. Indels were found within species belonging to sectionsRobur andCerris of genusQuercus and also between species of the 2 sections. In sectionRobur (Quercis robur L.,Quercus petraea [Matt.] Liebl.,Quercus pubescens Willd.), we detected rare alleles with an indel of 57 bp or 62 bp followed by a smaller indel of 12 bp in the SSR flanking regions. These alleles show a size range overlapping with that of alleles amplified inQuercus cerris L. (sectionCerris). Multiple alignments with sequences of sectionRobur revealed the same SSR repeat motif but multiple indels in SSR flanking regions inQ. cerris. We discuss the effects of size homoplasy of SSR loci for the study of interspecific gene flow and on estimates of population differentiation.     

Dwarfs and cannibals in the Arctic: production of Arctic char (Salvelinus alpinus (L.)) at two trophic levels

Due to extensive cannibalism, Arctic char (Salvelinus alpinus (L.)) often represent the two highest trophic levels in Arctic freshwater ecosystem where Arctic char often is the only freshwater fish present. There is a general lack of char stock size and production estimates from Arctic lakes although high catchability and late maturation of large piscivorous individuals raise considerable management challenges because large growing forms are a valued resource. Here, we use mark-recapture to estimate the biomass of both invertebrate feeding dwarfs (60–150 mm) and their cannibalistic conspecifics (>150 mm) in a small Arctic lake at Bear Island (74.5°N, 19.0°E; 11.3 ha; mean depth 1.8 m). Biomass was 10.1 and 2.0 kg ha⁻¹ and production was 2.1 and 0.5 kg ha⁻¹ yr⁻¹ for dwarfs and cannibals, respectively. All the production of invertebrate feeding small char was removed by the cannibals. The low production of the Arctic lake ecosystems combined with high catchability of large piscivorous char indicates that these stocks may be particularly vulnerable to exploitation. We finally point out the similarity between Arctic and sub-arctic alpine populations of Arctic char in production and life-history parameters.     

Population growth and structure in a variable environment

When a population experiences temporal changes in the vital rates due to environmental or biotic variation, change is not only expected in the rate of population growth but also in the structure of the population. In this study we present a method for transforming observed patterns (notably how vital rates change with temperature) into functions that can be used in population growth models and analysis of population structure. The method is exemplified by applying it to cohort studies in different constant temperatures of four species of aphids, Lipaphis erysimi (K.), Metopolophium dirhodum (Wlk.), Rhopaliosiphum padi and Macrosiphum avenae (F.). We use piece-wise linear functions to transform the vital rates of the cohort studies. The lifespans are divided into phases, each phase having linear rates. A projection matrix is formulated, where the elements are temperature dependent fecundities, survivorships and developmental rates. The major result is, contrary to what theory predicts as reasonable (Caswell 1989), that population structure of these aphid species will become almost fixed although the temperature varies. This result is consistent with findings of earlier field studies (Wiktelius 1982). A fixed population structure implies that it is possible to calculate the population growth rate on the basis of intrinsic rates of increase. By simulating different temperature regimes we also show that initial oscillations in the population structure dampen out after a few days. After initial oscillations, calculations of population growth using intrinsic rates of increase are consistent with calculations made by a matrix model.     

Relative preference of Lygus hesperus (Hemiptera: Miridae) to selected host plants in the field

Abstract Information on host plant preference of agriculturally important insect pests, such as Lygus hesperus (Knight), can be helpful in predicting its occurrence and future movement among crop and non-crop host plants. A field study was conducted during 2005 and 2006 to evaluate the host preference of Lygus to cotton and four other host plants in the Texas High Plains, including alfalfa (Medicago sativa L.), wild sunflower (Helianthus annuus L.), Russian thistle (Salsola iberica L.) and pigweed (Amaranthus palmeri L.). Sampling for both nymphs and adults during 2005 (July to November) and 2006 (June to November) showed that alfalfa and Russian thistle were the two most preferred hosts out of the five hosts evaluated. Abundance of nymphs (numbers per 50 sweeps per host plant) during the sampling period also indicated the superior reproductive suitability of alfalfa and Russian thistle. Cotton appeared to be the least attractive host plant for Lygus when Russian thistle and alfalfa were available in the host mosaic. Seasonal abundance of Lygus was found to be lower during 2006 compared to 2005, which may be explained by the difference in rainfall patterns during these two years. In terms of species dominance, L. hesperus was the most dominant species in the sampled population followed by an inconsiderable fraction of L. elisus and L. lineolaris.