Synergistic effects of different food species on life-history traits of Daphnia galeata

In this paper we describe the life history consequences of feeding Daphnia galeata with different food types in different concentrations. We fed the animals with four concentrations of two green algae Scenedesmus obliquus and Chlamydomonas globosa, given separately as well as in a 1:1 mixture. Growth, reproduction and condition of the animals and consequently the intrinsic rate of population increase, r, increased with the concentration of the food for all three experimental series. The life history parameters measured were lowest in the animals raised on C. globosa. Animals fed on S. obliquus showed higher values for r. We observed a distinct synergistic effect of the two algal species: growth, reproduction, condition and r were significantly higher for the animals raised on the mixed media as compared to the animals raised on the mono-algal media. We conclude that the two algal species represented complementary food resources.     

Contrasting life-history traits of two sympatric smooth-hound species: implication for vulnerability

In this study, life-history traits (maximum and average size, size at maturity and fecundity) of two congeneric smooth-hounds, Mustelus mustelus and Mustelus punctulatus, which share a geographical distribution and experience a similar fishing exploitation, were estimated and compared between species. The results indicated a lower maximum and average size, a lower size at maturity and a higher fecundity in M. punctulatus compared with those in M. mustelus. Considering that these two species co-occur in the same areas and are caught by the same fishing gears, the results indicate a higher vulnerability to exploitation of M. mustelus compared with that of M. punctulatus.     

Sympatric distribution of two cryptic bat species across Europe

The analysis of echolocation calls and mitochondrial DNA sequences recently revealed the existence of two cryptic bat species in Western Europe which were regarded as 'Pipistrellus pipistrellus' for more than 200 years. We now present data on acoustic and genetic characters across Europe including a novel genetic marker from the nuclear genome. Intraspecific variation of end frequencies of echolocation calls did not differ between geographic regions and only a little overlap existed between the two species. Nuclear and mitochondrial DNA sequences for the two species were highly divergent. No evidence was found for additional cryptic species in this group. With the exception of Scandinavia, both species occur across the whole of Europe and largely overlap in their range. The distribution of the species using echolocation calls at higher frequencies extends further north and the same species is also more common in the south along the Mediterranean Sea.     

Responses to competition effects of two anuran tadpoles according to life-history traits

Experimental manipulations of the densities of two larval anurans, Pelodytes punctatus and Bufo bufo , showed that these species compete asymmetrically in semi-natural conditions. Growth, mass at metamorphosis, date of metamorphosis, and survival were used as measures of response to interspecific competition. A mechanistic approach was used to collect information on the behaviour of the two species in different conditions. The competitive superiority of Pelodytes at individual level was correlated with a larger body, faster growth rate, increased per capita competitive impact on conspecifics, and greater reduction in the availability of trophic and spatial resources. In the presence of Pelodytes, Bufo showed slower growth, smaller size at metamorphosis and reduced survival. In the interspecific treatments Bufo individuals modified their behaviour by increasing activity and use of the water column while Pelodytes did not change their foraging activity or space use in the aquaria. However, the presence of Bufo resulted in a reduced larval period and smaller size at metamorphosis. We hypothesise that the presence of Bufo act as a signal of environmental degradation and shorten the larval period of Pelodytes, a typical temporal pond breeder . The smaller Bufo tadpoles are potentially stronger competitors at population level because they use relatively large amounts of energy (greater densities and higher metabolic rates). Consequently, they use larger proportions of the shared resources than their larger competitor. A possible evolutionary response for larger tadpoles is the development of interference mechanisms or "escaping" from ephemeral ponds where mortality by drying represent a high risk.     

Thermal reaction norms in two Coenagrion damselfly species: contrasting embryonic and larval life-history traits

1. We studied the temperature‐dependence of important life‐history traits both at the embryonic (egg hatching success, embryonic development time and hatchling size) and the larval stage (larval growth rate, larval survival and larval size after 100 days) using full‐sib families of two congeneric damselflies, Coenagrion hastulatum and Coenagrion puella, that differ in latitudinal distribution. Larvae were reared in the laboratory from the egg stage at four temperatures (12, 17, 22 and 27 °C). 2. The observed patterns of thermal plasticity in embryonic traits showed that the northern species was more successful than the southern species at lower temperatures, in line with the pattern of temperature adaptation in thermal reaction norms. 3. At the larval stage, we found no consistent pattern of latitudinal compensation. The thermal family reaction norms indicate, however, the potential for latitudinal compensation to evolve. We observed an ontogenetic shift in thermal optima for larval growth rate, with a higher optimal temperature for growth rate during the first 2 weeks of the larval stage. 4. This is the first indication of the existence of latitudinal compensation at the interspecific level in an invertebrate; it is stage‐specific, being present only in the embryonic stage. We argue that compensation in the embryonic stage may be much more likely than in the larvae and stress the importance of including more then one life‐history stage when drawing conclusions about the adaptiveness of patterns in thermal reaction norms.     

Spatial and temporal variation in a suite of life-history traits in two species of wolf spider

Abstract.  1. Life-history traits and density were assayed in seven populations of two sympatric species of wolf spider for three consecutive years. The goal of the study was to quantify population dynamics and its relation to spatial and temporal life-history variation.
2. Adult female body size and fecundity varied significantly, among field sites and among years, in both species. Female spiders of both species differed in mean relative reproductive effort among sites, but not among years. The size of offspring was invariable, with no significant differences due to site or year.
3. All populations of both species tended to either decrease or increase in density during a given year and this was tightly correlated with changes in prey consumption rates.
4. Since life-history patterns are determined primarily by selection, it is concluded that size at sexual maturity for females is phenotypically plastic and responds to changes in prey availability. Offspring size however is not plastic and it is likely that other selection forces have determined offspring size. Temporal fluctuations in population size are correlated over a large area relative to dispersal capabilities for these species and conservation efforts for invertebrates must take this into consideration.     

Climatic effects on life-history traits of moose in Estonia

Weather variables can influence life-history traits of ungulates. In this study, we assessed the suitability of regional climate indices including the NAO and two measures of local climate—the maximal extent of ice on the Baltic Sea (MIE) and absolute values of its annual deviations from the multi-year mean (VMIE)—to examine how density-independent processes influence moose body size and fecundity. We predicted that both winter severity (large values of MIE) and variability (large values of VMIE) depress moose traits (e.g., severe winters increase energy expenditure because of large snow depth or low temperatures, while the warmer than average winters may impose greater energetic demands on thermoregulation due to wet and windy weather, or may have indirect negative effects on summer foraging conditions). We estimated direct, delayed (lag) and cumulative effects of each climate measure. Both MIE and VMIE negatively affected jawbone length, with the effect size varying between the respective climatic indices and among age classes. In contrast to results obtained using local climatic variables, the NAO index had no significant effect on jawbone length. The probability of multiple ovulation was negatively influenced by direct effects of VMIE and delayed effects of MIE and NAO. We conclude that MIE and VMIE capture different aspects of the local climate and that these indices can be used in parallel as determinants of growth and fecundity of northern ungulates in coastal regions of the Baltic Sea.     

Density effects on life-history traits of an island lizard population

Long-term monitoring of life-history traits and the effects of density upon them were studied in an island population of the lizardEumeces okadae. Although life-history traits such as clutch size, egg size and the proportion of mature reproductive females varied little over 7 years in the intact population, manipulation of density to simulate decreased population density enhanced juvenile growth rate, age at first reproduction, frequency of female reproduction and size-specific clutch mass. In particular, the proportion of mature females reproducing annually increased almost 10 times from 5.6% to 53.8% after the removal of some lizards. However, body size at first reproduction and egg size were almost identical under both high and low density conditions. This study suggests that there were strong density-dependent effects on several life-history traits and thatE. okadae attained a density close to the carrying capacity of the environment.     

Effects of life-history traits and species distribution on genetic structure at maternally inherited markers in European trees and shrubs

Aim To examine relationships between life‐history traits, ecological and chorological characteristics of woody plant species and patterns of genetic differentiation among populations as assessed by chloroplast DNA (cpDNA) markers, and to compare them with patterns previously described from nuclear markers. Location Europe. Methods Data on cpDNA variation were compiled for 29 temperate European broad‐leaved tree and shrub species. Six qualitative and three quantitative characters of the species were tested for their relationship with two parameters of genetic population differentiation (G_ST and N_ST). Both direct species comparisons and phylogenetically independent contrast analyses were performed. Results When the phylogeny was not taken into account, five characters were significantly related to levels of population differentiation. The relationship disappeared in all but two cases (distribution type and seed mass) when analyses controlled for phylogenetic relationships among species. Main conclusions The correlation between distribution type (boreal‐temperate or temperate) and cpDNA differentiation of temperate European woody plant species suggests that their Quaternary history, in particular the location and isolation of their glacial refugia, is an important determinant of their present‐day level of genetic structure. By contrast, the relationship between life‐history traits and genetic differentiation at maternally inherited markers is weaker, especially when phylogenetic effects are controlled for.     

Quantitative genetic approach for assessing invasiveness: geographic and genetic variation in life-history traits

Predicting the spread of invasive species is a challenge for modern ecology. Although many invasive species undergo genetic bottlenecks during introduction to new areas resulting in a loss of genetic diversity, successful invaders manage to flourish in novel environments either because of pre-adaptations or because important traits contain adaptive variation enabling rapid adaptation to changing conditions. To predict and understand invasion success, it is crucial to analyse these features. We assessed the potential of a well-known invader, the Colorado potato beetle (Leptinotarsa decemlineata), to expand north of its current range in Europe. A short growing season and harsh overwintering conditions are apparent limiting factors for this species’ range. By rearing full-sib families from four geographically distinct populations (Russia, Estonia, Poland, Italy) at two fluctuating temperature regimes, we investigated (a) possible differences in survival, development time, and body size among populations and (b) the amount of adaptive variation within populations in these traits. All populations were able to complete their development in cooler conditions than in their current range. A significant genotype–environment interaction for development time and body size suggests the presence of adaptive genetic variation, indicating potential to adapt to cooler conditions. The northernmost population had the highest survival rates and fastest development times on both temperature regimes, suggesting pre-adaptation to cooler temperatures. Other populations had minor differences in development times. Interestingly, this species lacks the classical trade-off between body size and development time which could have contributed to its invasion potential. This study demonstrates the importance of considering both ecological and evolutionary aspects when assessing invasion risk.     

Bacterial associates of two Caribbean coral species reveal species-specific distribution and geographic variability

Scleractinian corals harbor microorganisms that form dynamic associations with the coral host and exhibit substantial genetic and ecological diversity. Microbial associates may provide defense against pathogens and serve as bioindicators of changing environmental conditions. Here we describe the bacterial assemblages associated with two of the most common and phylogenetically divergent reef-building corals in the Caribbean, Montastraea faveolata and Porites astreoides. Contrasting life history strategies and disease susceptibilities indicate potential differences in their microbiota and immune function that may in part drive changes in the composition of coral reef communities. The ribotype structure and diversity of coral-associated bacteria within the surface mucosal layer (SML) of healthy corals were assessed using denaturing gradient gel electrophoresis (DGGE) fingerprinting and 454 bar-coded pyrosequencing. Corals were sampled at disparate Caribbean locations representing various levels of anthropogenic impact. We demonstrate here that M. faveolata and P. astreoides harbor distinct, host-specific bacteria but that specificity varies by species and site. P. astreoides generally hosts a bacterial assemblage of low diversity that is largely dominated by one bacterial genus, Endozoicomonas, within the order Oceanospirillales. The bacterial assemblages associated with M. faveolata are significantly more diverse and exhibit higher specificity at the family level than P. astreoides assemblages. Both corals have more bacterial diversity and higher abundances of disease-related bacteria at sites closer to the mainland than at those furthest away. The most diverse bacterial taxa and highest relative abundance of disease-associated bacteria were seen for corals near St. Thomas, U.S. Virgin Islands (USVI) (2.5 km from shore), and the least diverse taxa and lowest relative abundance were seen for corals near our most pristine site in Belize (20 km from shore). We conclude that the two coral species studied harbor distinct bacterial assemblages within the SML, but the degree to which each species maintains specific microbial associations varies both within each site and across large spatial scales. The taxonomic scale (i.e., phylum versus genus) at which scientists examine coral-microbe associations, in addition to host-elicited factors and environmental fluctuations, must be considered carefully in future studies of the coral holobiont.     

The effects of warming on the ecophysiology of two co-existing kelp species with contrasting distributions

The northeast Atlantic has warmed significantly since the early 1980s, leading to shifts in species distributions and changes in the structure and functioning of communities and ecosystems. This study investigated the effects of increased temperature on two co-existing habitat-forming kelps: Laminaria digitata, a northern boreal species, and Laminaria ochroleuca, a southern Lusitanian species, to shed light on mechanisms underpinning responses of trailing and leading edge populations to warming. Kelp sporophytes collected from southwest United Kingdom were maintained under 3 treatments: ambient temperature (12 °C), +3 °C (15 °C) and +6 °C (18 °C) for 16 days. At higher temperatures, L. digitata showed a decline in growth rates and Fv/Fm, an increase in chemical defence production and a decrease in palatability. In contrast, L. ochroleuca demonstrated superior growth and photosynthesis at temperatures higher than current ambient levels, and was more heavily grazed. Whilst the observed decreased palatability of L. digitata held at higher temperatures could reduce top-down pressure on marginal populations, field observations of grazer densities suggest that this may be unimportant within the study system. Overall, our study suggests that shifts in trailing edge populations will be primarily driven by ecophysiological responses to high temperatures experienced during current and predicted thermal maxima, and although compensatory mechanisms may reduce top-down pressure on marginal populations, this is unlikely to be important within the current biogeographical context. Better understanding of the mechanisms underpinning climate-driven range shifts is important for habitat-forming species like kelps, which provide organic matter, create biogenic structure and alter environmental conditions for associated communities.     

Within- and between-generation effects of temperature on life-history traits in a butterfly

Non-genetic parental effects may largely affect offspring phenotype, and such plasticity is potentially adaptive. Despite its potential importance, little is known about cross-generational effects of temperature, at least partly because parental effects were frequently considered a troublesome nuisance, rather than a target of experimental studies. We here investigate effects of parental, developmental and acclimation temperature on life-history traits in the butterfly Bicyclus anynana. Higher developmental temperatures reduced development times and egg size, increased egg number, but did not affect pupal mass. Between-generation temperature effects on larval time, pupal time, larval growth rate and egg size were qualitatively very similar to effects of developmental temperature, and additionally affected pupal mass but not egg number. Parental effects are important mediators of phenotypic plasticity in B. anynana, and partly yielded antagonistic effects on different components of fitness, which may constrain the evolution of cross-generational adaptive plasticity.     

Integrating species life-history traits and patterns of deforestation in amphibian conservation planning

Aim  To identify priority areas for amphibian conservation in southeastern Brazil, by integrating species life-history traits and patterns of deforestation.
Location  State of São Paulo, Brazil.
Methods  We used the software M arxan to evaluate different scenarios of amphibian conservation planning. Our approach differs from previous methods by explicitly including two different landscape metrics; habitat split for species with aquatic larvae, and habitat loss for species with terrestrial development. We evaluated the effect of habitat requirements by classifying species breeding habitats in five categories (flowing water, still water permanent, still water temporary, bromeliad or bamboo, and terrestrial). We performed analyses using two scales, grid cells and watersheds and also considered nature preserves as protected areas.
Results  We found contrasting patterns of deforestation between coastal and inland regions. Seventy-six grid cells and 14 watersheds are capable of representing each species at least once. When accounting for grid cells already protected in state and national parks and considering species habitat requirements we found 16 high-priority grid cells for species with one or two reproductive habitats, and only one cell representing species with four habitat requirements. Key areas for the conservation of species breeding in flowing and permanent still waters are concentrated in southern state, while those for amphibians breeding in temporary ponds are concentrated in central to eastern zones. Eastern highland zones are key areas for preserving species breeding terrestrially by direct or indirect development. Species breeding in bromeliads and bamboos are already well represented in protected areas.
Main conclusions  Our results emphasize the need to integrate information on landscape configuration and species life-history traits to produce more ecologically relevant conservation strategies.     

Feedback effects of chronic browsing on life-history traits of a large herbivore

1. Increasing ungulate populations are affecting vegetation negatively in many areas, but few studies have assessed the long-term effects of overbrowsing on individual life-history traits of ungulates. 2. Using an insular population of white-tailed deer (Odocoileus virginianus Zimmermann; Anticosti, Québec, Canada) introduced in 1896, and whose density has remained high since the first evidence of severe browsing in the 1930s, we investigated potential feedbacks of long-term and heavy browsing on deer life-history traits. 3. We assessed whether chronic browsing contributed to a decline of the quality of deer diet in early autumn during the last 25 years, and evaluated the impacts of reduced diet quality on deer body condition and reproduction. 4. Rumen nitrogen content declined 22% between two time periods, 1977-79 and 2002-04, indicating a reduction in diet quality. 5. After accounting for the effects of year within the time period, age and date of harvest in autumn, peak body mass of both sexes declined between the two time periods. At the end of November, males were on average 12% heavier and adult does 6% heavier in 1977-79 than in 2002-04. Hind foot length did not vary between time periods. 6. The probability of conception increased 15% between the two time periods, but litter size at ovulation declined 7%, resulting in a similar total number of ovulations in 2002-04 and in 1977-79. 7. Our results suggest that following a decline in diet quality, white-tailed deer females modified their life-history strategies to maintain reproduction at the expense of growth. 8. Deer appear to tolerate drastic reductions in diet quality by modifying their life history traits, such as body mass and reproduction, before a reduction in density is observed. Such modifications may contribute to maintain high population density of large herbivores following population irruption.     

Predation effects on the evolution of life-history traits in a clonal oligochaete

Although size at maturity and size and number of offspring are life-history traits widely studied in sexual and parthenogenetic reproduction, there is no such research on animals reproducing asexually without the involvement of gametes. Here we present an individual-based model in combination with experiments to study the clonal growth of Stylaria lacustris, an oligochaete reproducing through fission. We studied the effect of individual size at fission and fission ratio on clone fitness. Our results show that in benign environments without predators, fitness is higher when small worms produce small offspring. Then we included size-specific sublethal predation and found that the fitness of the clone is maximized when parental worms start fission at a large size and produce large descendants intercalated in the middle of the parental worm's body. These results agree with empirical findings. Furthermore, the results of our own laboratory experiment revealed that when S. lacustris is exposed to chemical alarm signals from injured conspecifics, it alters its life history in the same direction as predicted by the model. Our findings suggest that the effect of size-specific sublethal predation is similar to the effect of size-specific lethal predation because both modes of predation result in size-dependent prey mortality.     

Saturating effects of species diversity on life-history evolution in bacteria

Species interactions can play a major role in shaping evolution in new environments. In theory, species interactions can either stimulate evolution by promoting coevolution or inhibit evolution by constraining ecological opportunity. The relative strength of these effects should vary as species richness increases, and yet there has been little evidence for evolution of component species in communities. We evolved bacterial microcosms containing between 1 and 12 species in three different environments. Growth rates and yields of isolates that evolved in communities were lower than those that evolved in monocultures, consistent with recent theory that competition constrains species to specialize on narrower sets of resources. This effect saturated or reversed at higher levels of richness, consistent with theory that directional effects of species interactions should weaken in more diverse communities. Species varied considerably, however, in their responses to both environment and richness levels. Mechanistic models and experiments are now needed to understand and predict joint evolutionary dynamics of species in diverse communities.