Differences In Life History Characteristics Research Articles

Accurate Monitoring of Submerged Aquatic Vegetation in a Macrophytic Lake Using Time-Series Sentinel-2 Images

Submerged aquatic vegetation (SAV) is one of the most important biological groups in shallow lakes ecosystems, and it plays a vital role in stabilizing the structure and function of water ecosystems. The study area of this research is Baiyangdian, which is a typical macrophytic lake with complex land cover types. This research aims to solve the low accuracy problem of the remote sensing extraction of SAV, which is mainly caused by water level fluctuations, differences in life-history characteristics, and mixed-pixel phenomena. Here, we developed a phenology–pixel method to determine the spatial distribution of SAV and the start and end dates of its growing season by using all Sentinel-2 images collected over a year on the Google Earth Engine platform. The experimental results show the following: (1) The phenology–pixel algorithm can effectively identify the maximum spatial distribution and growth period of submerged aquatic vegetation in Baiyangdian Lake throughout the year. The unique normalized difference vegetation index (NDVI) peak characteristics of Potamogeton crispus from March to May were used to effectively distinguish it from the low Phragmites australis population. Textural features based on the modified normalized difference water index (MNDWI) index effectively removed the mixed-pixel phenomenon of macrophytic lakes (such as dikes and sparse reeds). (2) A complete five-day interval NDVI time-series dataset was obtained, which removes potential noise on the temporal scale and fills in noisy observations by the harmonic analysis of time series (HANTS) method. We determined the two phenological periods of typical SAV by analyzing the intrayear variation characteristics of NDVI and MNDWI. (3) Using field-survey data for accuracy verification, the overall accuracy of our method was determined to be 94.8%, and the user’s accuracy and producer’s accuracy were 93.3% and 87.3%, respectively. Determining the temporal and spatial distribution of different SAV populations provides important technical support for actively promoting the maintenance and reconstruction of lake and reservoir ecosystems.

Diet influences latitudinal gradients in life-history traits, but not reproductive output, in ectotherms.

Latitudinal gradients in life-history traits are apparent in many taxa and are expected to be strong for ectotherms that have temperature-driven constraints on performance and fitness. The strength of these gradients, however, should also be affected by diet. Because diet type (carnivory, omnivory, herbivory) influences accessibility to nutrition and assimilation efficiency, we aim to study how diet affects latitudinal gradients in lifetime reproductive output and the underlying life-history traits in ectotherms. Global. Recent. Lizards (Reptilia, Squamata, Sauria). We used empirical (352 species) and phylogenetically imputed data (563 species) to analyse the interactive effects of latitude and diet on life-history traits (longevity, age at maturity, reproductive life span, hatchling mass, clutch/brood size, clutch/brood frequency, female mass) and lifetime reproductive output of lizards. Lifetime reproductive output does not significantly differ in lizards across diet types, and only carnivores exhibit a small increase at higher latitudes. Diet type, however, influences latitudinal patterns of individual life-history traits. Carnivores exhibit a shift towards 'slower-paced' life histories at higher latitudes for most traits (increased longevity, age at maturity, reproductive life span, and decreased clutch frequency). By contrast, herbivores either display 'faster-paced' life histories (reduction in reproductive life span, hatchling mass, female mass) or no change (clutch frequency, clutch size, age at maturity) at higher latitudes. Omnivores exhibit intermediate and muted latitudinal patterns. We suggest that the nutritional challenges of herbivory, compounded by thermal constraints at higher latitudes, may explain differences in life-history characteristics of herbivorous ectotherms. Intermediate patterns exhibited by omnivores highlight how flexibility in diet can buffer environmental challenges at higher latitudes. Our results indicate that lizards with different diet types display various trends in their life histories across latitudes, which eventually balance out to result in similar reproductive outputs throughout their lifetime, with little benefits to carnivory.

Lack of life history change in two over-exploited haddock (Melanogrammus aeglefinus) stocks

Concomitant with declines in abundance, many commercially exploited marine fishes have undergone significant life history changes that are critically important as they impact population growth rate and, thus, recovery rate of depleted stocks. By examining data collected as part of offshore surveys conducted during 1971–2012, we evaluated whether there have been changes in growth rate and size at maturity for haddock on Grand Bank and St. Pierre Bank, two over-exploited stocks at the northern extremity of the species range in the western Atlantic Ocean. Contrary to expectation, we found no evidence for change in either growth or maturity since 1971. However, there were differences in life history characteristics between the two stocks, as well as between males and females. Although no difference in growth was observed between sexes, differences in maturation were evident with 50% of males maturing at ∼40cm and 50% of females maturing at ∼48cm. Haddock from Grand Bank were larger than haddock from St. Pierre Bank at ages 8 and 10 by 4.4% and 7.6%, respectively. We also found that haddock on Grand Bank matured at smaller sizes (length at which the probability of maturity was 50% was 38.2cm for males and 46.3cm for females) than those from St. Pierre Bank (42.1cm for males and 49.9cm for females). The haddock fishery off Newfoundland developed rapidly from 1945 but collapsed within less than two decades. Available information suggests that while fishery exploitation rates were undoubtedly high, haddock on Grand Bank and St. Pierre Bank may not have been exposed to sufficient multigenerational fishing pressure to generate decreases in growth and maturity timing as seen in other over-exploited stocks and appear to have maintained historic life history characteristics.

Differences in life history characteristics among three sympatric evolutionary species of the Rotaria rotatoria complex

The Bdelloidea rotifer, a kind of asexually microscopic invertebrate, is the largest Metazoan group that reproduces only through parthenogenesis. Here the potential evolutionary species composition was analyzed using a coalescent approach to infer independently evolving entities from a phylogenetic tree obtained from cytochrome oxidase I sequences. Three clones (HX4, HX8 and HX19) of Bdelloidea Rotaria rotatoria were selected to be the representatives of three sympatric putative cryptic taxa for detecting the effects of temperature (24, 28 and 32 ℃) on their life history traits. The results showed that the responses of life table parameters to increasing temperature were different among the three evolving entities. Evolutionary species, temperatures and their interaction significantly affected all life history parameters except that evolutionary species did not significantly affect the durations of post-reproductive period and mean lifespan. In addition, the interaction of evolutionary species and temperatures did not significantly affect the durations of post-reproductive period, offspring production or net reproductive rate. No matter what the evolutionary species was, the age-specific survival curves tended to decrease earlier and more quickly, and the peak of age-specific fecundity curves appeared earlier with increasing temperature. The three potential cryptic R. rotatoria taxa adopted variable life history strategies, low reproduction and high survivorship at low temperature, as well as high reproduction and low survivorship at high temperature. The similar adaptation abilities of HX4, HX8 and HX19 to water temperatures could be the best explanation for their coexistence in the subtropical shallow pond at a high temperature.

Root-Lesion Nematodes Suppress Cabbage Aphid Population Development by Reducing Aphid Daily Reproduction

Empirical studies have shown that belowground feeding herbivores can affect the performance of aboveground herbivores in different ways. Often the critical life-history parameters underlying the observed performance effects remain unexplored. In order to better understand the cause for the observed effects on aboveground herbivores, these ecological mechanisms must be better understood. In this study we combined empirical experiments with a modeling approach to analyze the effect of two root feeding endoparasitic nematodes with different feeding strategies on the population growth of the aboveground feeding specialist aphid Brevicoryne brassicae on Brassica nigra. The aim was to test whether emerging differences in life history characteristics (days until reproduction, daily reproduction) would be sufficient to explain observed differences in aphid population development on plants with and without two species of nematodes. Aphid numbers were lower on plants with Pratylenchus penetrans in comparison to aphid numbers on plants with Meloidogyne spp. A dedicated experiment showed that aphid daily reproduction was lower on plants with P. penetrans (3.08 offspring female–1 day–1) in comparison to both uninfested plants and plants with Meloidogyne spp. (3.50 offspring female–1 day–1). The species-specific reduction of aphid reproduction appeared independent of changes in amino acids, soluble sugars or the glucosinolate sinigrin in the phloem. An individual-based model revealed that relatively small differences in reproduction rate per female were sufficient to yield a similar difference in aphid populations as was found in the empirical experiments.

Variation in tropical bird survival across longitude and guilds: a case study from the Amazon

Survival estimates of tropical birds have been used to examine life‐history variation across latitudes and dietary guilds. Here, we provide apparent survival estimates of 31 rainforest species from central Amazonian Brazil and compare our results with estimates from Ecuador, Peru (western Amazonia) and French Guiana (eastern Amazonia) to examine geographic variation in demography. Our averaged annual survival estimate for central Amazonian species (ϕ= 0.59, SE = 0.10) was concordant with previously published estimates from the western Amazon (ϕ= 0.58, SE = 0.02), and eastern Amazon (ϕ= 0.63, SE = 0.06). Two predominate demographic patterns were detected across the study areas: within species, survival was highest or lowest in eastern or western Amazonia, but rarely in central Amazonia. The most striking demographic variation was exhibited by Pithys albifrons, for which apparent survival estimates were nearly twice as high in eastern Amazonia (ϕ= 0.80, SE = 0.06) than in western Amazonia (ϕ= 0.42, SE = 0.06) but intermediate in central Amazonia (ϕ= 0.54, SE = 0.04). Although variation in survival may be associated with differences in life history characteristics, our analysis of flocking guild, body size, and nest architecture revealed only moderate differences in survival associated with nest architecture. These results suggest that geographic variation in population processes may be significant for widespread Amazonian species.

Differences in life history characteristics between two sibling species inBrachionus calycifloruscomplex from tropical shallow lakes

The studies of differences in life history and suitability of both water temperatures and trophic levels among rotifer sibling species improve our understanding of speciation, sibling species coexistence and possible niche differentiation over space and time, and consequences for the functioning of ecosystems induced by climate change and eutrophication. We collected Brachionus calyciflorus from Lake Baixiang and Lake Kongque, two tropical shallow lakes, in Xishuangbanna city, Yunnan, China, clonally cultured them in laboratory, and found that the B. calyciflorus complex contains two sibling species named sibling species BNA13 and BNB3 by phylogenetic analysis, and investigated the life-table parameters of the two sibling species BNA13 and BNB3 at four temperatures (16, 20, 24 and 28°C) and four algal densities (0.5, 1.0, 2.0 and 4.0×106 cells.mL−1 ). The results showed that the responses to increasing temperature and algal density for each of the life-table parameters differed with rotifer sibling species. Sibling species, temperature, algal density and their interactions almost all significantly affected the durations of juvenile period, embryonic development, reproductive period, post-reproductive period, mean lifespan, net reproductive rate, generation time and intrinsic rate of population growth. Sibling species significantly affected the age-specific survivorship. Temperature, algal density and their interaction and the interaction of sibling species and temperature significantly affected the age-specific fecundity. Regardless of the effects of temperature and algal density, the durations of juvenile period, embryonic development, reproductive period, post-reproductive period and mean lifespan, age-specific survivorship, net reproductive rate and generation time of the B. calyciflorus sibling species BNA13 were greater than those of BNB3, but the intrinsic rate of population growth of BNA13 was lower than those of BNB3. This suggests that the two B. calyciflorus sibling species adopted variable life history strategies, low population growth and high survivorship for sibling species BNA13, and high population growth and low survivorship for sibling species BNB3. Both the intrinsic rates of population growth of BNA13 and BNB3 were the highest at 28°C and 4.0×106 cells.mL−1 algal density, indicating that some adaptations of the B. calyciflorus sibling species BNA13 and BNB3 in tropical shallow lakes to water temperatures and trophic levels were similar, and they have the potential for coexistence in single waterbody of higher temperature and higher trophic level.

Multilocus phylogeography of Australian teals (Anasspp.): a case study of the relationship between vagility and genetic structure

Biogeographic barriers potentially restrict gene flow but variation in dispersal or vagility can influence the effectiveness of these barriers among different species and produce characteristic patterns of population genetic structure. The objective of this study was to investigate interspecific and intraspecific genetic structure in two closely related species that differ in several life-history characteristics. The grey teal Anas gracilis is geographically widespread throughout Australia with a distribution that crosses several recognized biogeographic barriers. This species has high vagility as its extensive movements track broad-scale patterns in rainfall. In contrast, the closely related chestnut teal A. castanea is endemic to the mesic southeastern and southwestern regions of Australia and is more sedentary. We hypothesized that these differences in life-history characteristics would result in more pronounced population structuring in the chestnut teal. We sequenced five nuclear loci (nuDNA) for 49 grey teal and 23 chestnut teal and compared results to published mitochondrial DNA (mtDNA) sequences. We used analysis of molecular variance to examine population structure, and applied coalescent based approaches to estimate demographic parameters. As predicted, chestnut teal were more strongly structured at both mtDNA and nuDNA (ΦST= 0.163 and 0.054, respectively) than were grey teal (ΦST < 0.0001 for both sets of loci). Surprisingly, a greater proportion of the total genetic variation was partitioned among populations within species (ΦSC= 0.014 and 0.047 for nuDNA and mtDNA, respectively) than between the two species (ΦCT < 0.0001 for both loci). The ‘Isolation with Migration’ coalescent model suggested a late Pleistocene divergence between the taxa, but remarkably, a deeper divergence between the southeastern and southwestern populations of chestnut teal. We conclude that dispersal potential played a prominent role in the structuring of populations within these species and that divergent selection associated with ecology and life history traits likely contributed to rapid and recent speciation in this pair.

Stochastic Population Dynamics and Life-History Variation in Marine Fish Species

We examined whether differences in life-history characteristics can explain interspecific variation in stochastic population dynamics in nine marine fish species living in the Barents Sea system. After observation errors in population estimates were accounted for, temporal variability in natural mortality rate, annual recruitment, and population growth rate was negatively related to generation time. Mean natural mortality rate, annual recruitment, and population growth rate were lower in long-lived species than in short-lived species. Thus, important species-specific characteristics of the population dynamics were related to the species position along the slow-fast continuum of life-history variation. These relationships were further associated with interspecific differences in ecology: species at the fast end were mainly pelagic, with short generation times and high natural mortality, annual recruitment, and population growth rates, and also showed high temporal variability in those demographic traits. In contrast, species at the slow end were long-lived, deepwater species with low rates and reduced temporal variability in the same demographic traits. These interspecific relationships show that the life-history characteristics of a species can predict basic features of interspecific variation in population dynamical characteristics of marine fish, which should have implications for the choice of harvest strategy to facilitate sustainable yields.

Timing of seasonal migration in mule deer: effects of climate, plant phenology, and life-history characteristics

Phenological events of plants and animals are sensitive to climatic processes. Migration is a life-history event exhibited by most large herbivores living in seasonal environments, and is thought to occur in response to dynamics of forage and weather. Decisions regarding when to migrate, however, may be affected by differences in life-history characteristics of individuals. Long-term and intensive study of a population of mule deer (Odocoileus hemionus) in the Sierra Nevada, California, USA, allowed us to document patterns of migration during 11 years that encompassed a wide array of environmental conditions. We used two new techniques to properly account for interval-censored data and disentangle effects of broad-scale climate, local weather patterns, and plant phenology on seasonal patterns of migration, while incorporating effects of individual life-history characteristics. Timing of autumn migration varied substantially among individual deer, but was associated with the severity of winter weather, and in particular, snow depth and cold temperatures. Migratory responses to winter weather, however, were affected by age, nutritional condition, and summer residency of individual females. Old females and those in good nutritional condition risked encountering severe weather by delaying autumn migration, and were thus risk-prone with respect to the potential loss of foraging opportunities in deep snow compared with young females and those in poor nutritional condition. Females that summered on the west side of the crest of the Sierra Nevada delayed autumn migration relative to east-side females, which supports the influence of the local environment on timing of migration. In contrast, timing of spring migration was unrelated to individual life-history characteristics, was nearly twice as synchronous as autumn migration, differed among years, was related to the southern oscillation index, and was influenced by absolute snow depth and advancing phenology of plants. Plasticity in timing of migration in response to climatic conditions and plant phenology may be an adaptive behavioral strategy, which should reduce the detrimental effects of trophic mismatches between resources and other life-history events of large herbivores. Failure to consider effects of nutrition and other life-history traits may cloud interpretation of phenological patterns of mammals and conceal relationships associated with climate change.

Growth, Activity, and Survivorship from Three Sympatric Parthenogenic Whiptails (Family Teiidae)

We surveyed whiptail lizard populations for seven summers (2000–2006) in riparian forests along the Rio Grande in central New Mexico. We captured 5,382 individuals from three parthenogenic species (Aspidoscelis exsanguis, Aspidoscelis neomexicana, and Aspidoscelis uniparens) including 129 hatchlings (young-of-the-year) that were later recaptured as adults. Growth data were fit to a logistic growth model and compared using a likelihood ratio test. Comparisons of growth rates showed that A. exsanguis grew faster than both A. neomexicana and A. uniparens and attained a larger snout–vent length (SVL). Comparisons of capture rates showed that species had similar activity patterns during the summer. Captures of adults peaked in mid-June and decreased in August. Hatchlings became active at the end of July and captures peaked in September. Some individuals were captured several seasons indicating that lizards lived for at least 3–4 yr. Our study shows both similarities and differences in life-history characteristics for three closely related and coexisting whiptail species.

Do differences in life history exist for blacktip sharks, Carcharhinus limbatus, from the United States South Atlantic Bight and Eastern Gulf of Mexico?

We examined life history traits (e.g., mean length-at-age, growth rate, age-at-maturity) for blacktip sharks collected from two separate geographical areas (eastern Gulf of Mexico and South Atlantic Bight) to address the potential for separate stocks in southeastern US waters. Samples were obtained from fishery-dependent and independent sources. Growth and logistic models were fitted to observed length-at-age and reproductive data, respectively. von Bertalanffy growth parameters derived for blacktip shark from the Gulf of Mexico show that they attain a statistically smaller theoretical maximum length (L ∞ = 141.6 cm vs. L ∞ = 158.5 cm for female and L ∞ = 126.0 cm FL and L ∞ = 147.4 cm FL for male) and have a faster growth rate (k = 0.24 yr−1 vs. k = 0.16 yr−1 for female and k = 0.27 yr−1 vs. k = 0.21 yr−1 for male) than conspecifics in the South Atlantic Bight. Median length- and age-at-maturity were significantly different between sex and area. Length at which 50% of the population is mature was 117.3 cm FL for females and 103.4 cm FL for males in the Gulf of Mexico and 126.6 cm FL for females and 116.7 cm FL for males in the South Atlantic Bight. Median age-at-maturity was 5.7 yrs and 4.5 yrs for females and males in the Gulf of Mexico, respectively, while age-at-maturity was 6.7 yrs for females and 5.0 yrs for males for sharks from the South Atlantic Bight. Due to varying statistical results, temporal problems of sampling, and potential for gear bias, we could not definitively conclude that differences in life history characteristics exist.

Asymmetric indirect interactions mediated by a shared parasitoid: connecting species traits and local distribution patterns for two chrysomelid beetles

This paper reports on an asymmetric indirect interaction between two chrysomelid beetles where one species (Galerucella tenella) experiences higher parasitization, and the other species (Galerucella calmariensis) lower parasitization, in mixed compared with monospecific populations. This pattern is likely to be a consequence of differences in life history characteristics, where the inferior species has a smaller body size, a lower fecundity and supports a lower parasitoid density than the superior species. This connection between life history characteristics and interspecific dominance in host-parasitoid systems corresponds to predictions from current community ecology theory, and provides a useful building-block in the development of a predictive theory of parasitoid effects on host coexistence.

Local Interactions in Pitcher Plant Communities Scale-Up to Regional Patterns in Distribution and Abundance

We used the aquatic communities living in the purple pitcher plant (Sarracenia purpurea L., Sarraceniaceae) to determine if patterns produced by trophic interactions at the local scale can be detected at larger spatial scales. Mosquitoes (Wyeomyia smithii Coq., Diptera: Culicidae) are known to have a negative effect on the aquatic microfauna within leaves. We compared the abundance of two microfaunal taxa, Bodo (Kinetoplastea: Bodonidae) and Habrotrocha rosa Donner (Rotifera: Bdelloidea), in bogs with and without pitcher plant mosquitoes. Bogs containing pitcher plant mosquitoes had lower densities of bacteria through the study period. However, within these bogs, leaves with mosquitoes did not have lower bacterial densities. We found that the pattern for Bodo was similar at the leaf and bog spatial scales. Abundance of Bodo was closely linked to bacterial densities and the presence of mosquitoes strengthened that relationship, because of greater predator impacts when bacteria were scarce. In contrast, different patterns emerged at the two scales for H. rosa. At the leaf scale, a predator effect was seen only for low bacterial densities (as for Bodo), but at the bog scale, H. rosa was less abundant in mosquito bogs, and abundance was not associated with bacterial levels. We suggest that differences in life history characteristics (population growth rate and average abundance) may influence the relative influence of local interactions and regional processes such as colonization.

Observed Differences in Life History Characteristics of Nematodes Aphelenchus and Acrobeloides upon Exposure to Copper and Benzo(a)pyrene

Maturity index values reflect life history characteristics often inferred by morphology. We tested the hypothesis that Acrobeloides and Aphelenchus are sensitive to chemical pollutants, opposite of what their colonizer-persister (CP) value of 2 suggests. Acrobeloides and Aphelenchus were reared at 19 degrees C and provided diets of Escherichia coli and Rhizoctonia solani, respectively. LC50 values for Aphelenchus exposed to copper or benzo(a)pyrene (BaP) are greater than Acrobeloides. Copper impedes growth of Acrobeloides at 10 microg/g, and results in 100% mortality at 20 microg/g. In contrast, Aphelenchus is more resilient, with no visible impact at 20 microg/g. Acrobeloides and Aphelenchus were sensitive to much lower concentrations of BaP than copper, i.e., 0.5 microg/g inhibited development of Acrobeloides and 2 microg/g for Aphelenchus. Egg size and hatch were unaffected at 15 microg/g copper. In contrast, 0.5 microg/g BaP reduced both egg size and hatch for Aphelenchus but not Acrobeloides. Survival of Acrobeloides and reproduction of Aphelenchus responded differently to copper and BaP, implying the relationship between this classification and their sensitivity to short-term effects may be less straightforward than presumed. Refinement of index values based on empirical evidence can be used to improve sensitivity and interpretation of nematode community indices for environmental monitoring.

Examination of the responses of slimy sculpin (Cottus cognatus) and white sucker (Catostomus commersoni) collected on the Saint John River (Canada) downstream of pulp mill, paper mill, and sewage discharges.

As part of a larger survey on cumulative effects within the Saint John River basin (Canada), a fish survey was conducted near Edmundston (NB, Canada) in the fall of 1999 using slimy sculpin (Cottus cognatus) and white sucker (Catostomus commersoni). The discharge environment receives effluent from the pulp mill, a paper mill, three sewage discharges, and tributaries receiving agricultural runoff. Sculpin collected downstream of the sewage discharges and pulp mill effluent had greater growth, condition, and liver size but no significant differences in gonad size. Stable isotope data indicated slimy sculpin did not move between sites. Female sculpin collected downstream of the paper mill showed no significant differences in length, body weight, age, condition factor, liver size, and gonad size compared to fish from reference sites. Female white sucker collected downstream of the pulp mill did not differ significantly in any measured parameter compared to reference fish. Liver sizes of white sucker from the Saint John River were outside the range considered to be indicative of uncontaminated riverine sites. In 2000, sculpin collected downstream from a poultry-processing facility had larger livers and lower condition factors, suggesting that the site is contaminated. We found no significant differences in sculpin length, weight, condition (except for males), and liver size in sculpin collected downstream from the pulp mill in October 2001. The responses of slimy sculpin and white sucker differed, perhaps in relation to differences in life history characteristics. Results from this study indicate the slimy sculpin is a suitable fish species for monitoring rivers that receive multiple industrial and municipal effluents.

DIFFERENCES IN LIFE‐HISTORY CHARACTERISTICS ARE CONSISTENT WITH THE VERTICAL DISTRIBUTION PATTERN OF FUCUS SERRATUS AND FUCUS VESICULOSUS (FUCALES, PHAEOPHYCEAE) IN THE CENTRAL BALTIC SEA

On the rocky shores of southeast Sweden, in the central Baltic Sea, the brown seaweed species Fucus serratus L. and Fucus vesiculosus L. form dense constantly submerged stands. The relative proportion of the two species in the belt is shifting both vertically and geographically. Our hypothesis is that differences in life‐history characteristics and the tolerance to physical factors such as wave force, freezing, and light may alter the competitive outcome between the two species with increasing wave exposure. This study included a combination of field studies and laboratory experiments. In sheltered locations, F. serratus and F. vesiculosus grow in mixed stands from 0.5 to 3 m deep, whereas at exposed sites F. vesiculosus grow from 0.5 to 2 m deep and F. serratus mainly from 1 to 5 m deep. The two Fucus species differed markedly in their tolerance to physical stress as well as in a number of reproductive and vegetative characteristics. Tolerance to freezing and wave action was higher in F. vesiculosus compared with F. serratus. Fucus vesiculosus also produced 10 times more eggs per receptacle, allocated significantly more tissue per frond for reproduction, and produced more reproductive fronds per individual than did F. serratus. In addition, the survival rate of F. vesiculosus germlings was slightly higher than that of F. serratus germlings during the first year. These differences in life history characteristics are suggested to partly explain the observed distribution patterns of the two Fucus species in the Baltic Sea.

Caddisfly life histories along permanence gradients in high‐altitude wetlands in Colorado (U.S.A.)

SUMMARY1. Larvae of cased caddisflies (Limnephilidae and Phryganeidae) are among the most abundant and conspicuous invertebrates in northern wetlands. Although species replacements are often observed along permanence gradients, the underlying causal mechanisms are poorly understood. In this paper, we report on the distributional patterns of caddisflies in permanent and temporary high‐altitude ponds, and how those patterns reflect differences in life history characteristics that affect desiccation tolerance (fundamental niches) versus constraints related to biotic interactions (realised niches).2. Species (Hesperophylax occidentalisandAgrypnia deflata) that were encountered only in permanent ponds are restricted in distribution by life history (no ovarian diapause, aquatic oviposition, and/or inability to tolerate desiccation). Although the egg masses ofH. occidentalistolerate desiccation, the larvae leave the protective gelatinous matrix of the egg mass because adults oviposit in water.3. Three species (Asynarchus nigriculus, Limnephilus externusandL. picturatus) have life history characteristics (rapid larval growth, ovarian diapause and terrestrial oviposition of desiccation‐tolerant eggs) that should facilitate the use of both permanent and temporary habitats. However,A. nigriculusis rare or absent in most permanent ponds, andL. externusandL.picturatusare rare or absent in most temporary ponds. Experimental data from a previous study on the combined effects of salamander predation and interspecific interactions among caddisflies (e.g. intraguild predation) suggest that biotic interactions limit each species to a subset of potentially exploitable habitats.4. Many wetland invertebrates exhibit species replacements along permanence gradients, but few studies have separated the relative importance of the effects of dryingper sefrom the effects of biotic interactions. Our results emphasise the complementary roles of comparative data on life histories and experimental data on competition and predation for understanding invertebrate distributions along permanence gradients.

Life-history Characteristics, Population Structure, and Contribution of Hatchery and Wild Steelhead in a Lake Huron Tributary

Life-history characteristics, size structure, and relative composition of hatchery-reared and wild-produced steelhead Oncorhynchus mykiss in the Carp River, Michigan, were examined to determine if population attributes were similar between origins. Quantitative scale analyses were used to determine the origin and life-history attributes of adult fish captured during their spring spawning migration from 1995–1998. Hatchery males and females comprised 40% and 23%, respectively, of the spawning migration, while wild males and females comprised 19% and 18%, respectively. Male and female hatchery steelhead had shorter stream-residence durations (1 year) than wild fish (2 years). Both genders of hatchery individuals also reached reproductive maturity at younger ages (males, 3 years; females, 4 years) than wild fish (5 years). The number of years between repeat-spawning events was the same (1 year), irrespective of gender or origin. However, the number of fish captured during repeat-spawning events differed between origins (hatchery males: 42%; wild males: 9%; hatchery females: 23%; and wild females: 26%). The median number of years in lake residence prior to maiden spawning did not differ between hatchery and wild fish (males, 2 years; females, 3 years). Median length-at-age estimates differed between hatchery and wild male steelhead at age 4 (66 cm and 58 cm, respectively), while the median length-at-age for all other age classes did not differ, irrespective of gender and origin. Our results suggest that differences in life-history characteristics exist between hatchery-reared and wild-produced Carp River steelhead, and that system-specific management objectives should be considered prior to the initiation of stocking efforts.

Development and reproduction of a predatory stinkbug, Podisus nigrispinus in relation to two different prey types and environmental conditions

Abiotic factors, prey availability, prey type, and plant host actsimultaneously under field conditions. Their combined effects werepartially investigated for the predatory stinkbugPodisus nigrispinus(Dallas) (Heteroptera: Pentatomidae) preying on tomato leafminer (TLM)caterpillars Tuta absoluta (Meyrick)(Lepidoptera: Gelechiidae) (a preyfeeding on a plant host), and compared to yellow mealworm (YMW)Tenebrio molitor (Coleoptera: Tenebrionidae)pupae (a prey not feeding ona plant host). These experiments were carried out in the laboratory and inan open-sided greenhouse. In general, the environmental variationsbetween laboratory and open-sided greenhouse did not induce differencesin life history characteristics forP. nigrispinus feeding on the sameprey type. However, development and reproductionof P. nigrispinuswas greatly affected by prey type. Nymphal developmental times weresimilar between prey types under laboratory conditions; but were longer(and produced adults of lower body weight) when predators in theopen-sided greenhouse were fed on TLM compared with YMW. Mean mortalityduring the second instar was higher on both prey types in the open-sidedgreenhouse than in the laboratory. Adult emergencewas 38.5 and 50% inthe laboratory, and 32.5 and 48.6%in the open-sided greenhouse for bugsfed on TLM and YMW, respectively. Reproductive characteristics weresimilar for the different environmental conditions when the predator fed onthe same prey, but offspring production was greater for females fed on YMWcompared to females fed on TLM. These results suggest thatP. nigrispinus can adjust its performance accordingto the type of prey available, independently from environmentalvariations. It has the ability to survive on alternative prey,enabling it to maintain a presence in thetomato ecosystem until a primary pest species arrives.