Seasonal variation in life history traits in two Drosophila species

Seasonal environmental heterogeneity is cyclic, persistent and geographically widespread. In species that reproduce multiple times annually, environmental changes across seasonal time may create different selection regimes that may shape the population ecology and life history adaptation in these species. Here, we investigate how two closely related species of Drosophila in a temperate orchard respond to environmental changes across seasonal time. Natural populations of Drosophila melanogaster and Drosophila simulans were sampled at four timepoints from June through November to assess seasonal change in fundamental aspects of population dynamics as well as life history traits. D. melanogaster exhibit pronounced change across seasonal time: early in the season, the population is inferred to be uniformly young and potentially represents the early generation following overwintering survivorship. D. melanogaster isofemale lines derived from the early population and reared in a common garden are characterized by high tolerance to a variety of stressors as well as a fast rate of development in the laboratory environment that declines across seasonal time. In contrast, wild D. simulans populations were inferred to be consistently heterogeneous in age distribution across seasonal collections; only starvation tolerance changed predictably over seasonal time in a parallel manner as in D. melanogaster. These results suggest fundamental differences in population and evolutionary dynamics between these two taxa associated with seasonal heterogeneity in environmental parameters and associated selection pressures.     

Dietary differences between two co-occurring calanoid copepod species

Summary Two co-occurring high altitude calanoid copepods, Diaptomus shoshone Marsh and D. coloradensis Forbes are of different size: the former is approximately twice as long as the latter. There are also temporal differences in development: the former matures 2–3 weeks before the latter in most ponds. Gut analyses of copepodids and adults of both species indicate that D. shoshone eats larger food particles but that D. shoshone early copepodids eat particles similar in size to D. coloradensis adults. Morphology of feeding appendages partially explains the dietary differences. These data are discussed from the viewpoint of competition between the species; it is concluded that either temporal differences or size differences of copepodids and adults would allow coexistence and that extreme size differences are probably unimportant compared to morphological differences of feeding appendages and perhaps behavioral differences.Supported in part by a Tufts Faculty Research Award.     

Mixed interactions among life history stages of two harvested related species

Climate change and harvesting can affect the ecosystems'' functioning by altering the population dynamics and interactions among species. Knowing how species interact is essential for better understanding potentially unintended consequences of harvest on multiple species in ecosystems. I analyzed how stage‐specific interactions between two harvested competitors, the haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua), living in the Barents Sea affect the outcome of changes in the harvest of the two species. Using state‐space models that account for observation errors and stochasticity in the population dynamics, I run different harvesting scenarios and track population‐level responses of both species. The increasing temperature elevated the number of larvae of haddock but did not significantly influence the older age‐classes. The nature of the interactions between both species shifted from predator‐prey to competition around age‐2 to ‐3. Increased cod fishing mortality, which led to decreasing abundance of cod, was associated with an increasing overall abundance of haddock, which suggests compensatory dynamics of both species. From a stage‐specific approach, I show that a change in the abundance in one species may propagate to other species, threatening the exploited species'' recovery. Thus, this study demonstrates that considering interactions among life history stages of harvested species is essential to enhance species'' co‐existence in harvested ecosystems. The approach developed in this study steps forward the analyses of effects of harvest and climate in multi‐species systems by considering the comprehension of complex ecological processes to facilitate the sustainable use of natural resources.     

Habitat displacement effect between two competing owl species in fragmented forests

Many owl species use the same nesting and food resources, which causes strong interspecific competition and spatio-temporal niche separation. We made use of a recent colonisation of Ural Owls (Strix uralensis) in southern Poland to compare habitat preferences of Tawny Owls (Strix aluco) allopatry and sympatry with Ural Owls. We investigated spatial niche segregation of Ural Owl and the Tawny Owl in sympatry and compared habitat preferences of Tawny Owls breeding in allopatry and sympatry. Tawny Owls breeding in sympatry with Ural Owls occupied forests with higher canopy compactness, sites located closer to forest border and to built-up areas, as well as stands with a higher share of fir and spruce and a lower share of beech as compared to sites occupied by Ural Owls. Allopatric Tawny Owls occupied sites with lower canopy compactness and bred at sites located further from forest borders and in stands with lower share of fir and spruce and a higher share of deciduous as compared to sympatric Tawny Owls. As Ural owls are dominant in relation to Tawny Owls, this indicates that the presence of Ural Owls prevents Tawny Owls from occupying deciduous-dominated and old stands located in forest interior areas, far from buildings and forest edges. The results support habitat displacement between the two species when breeding in sympatry. We also show that protection of large forest patches is crucial for the Ural Owl, a species still rare in central Europe, while small patches are occupied by the abundant Tawny Owl.     

Effects of turbidity on life history parameters of two species of Daphnia

SUMMARY. 1. Life table experiments were carried out in a range of turbidities on D. pulex , representing a 'clear-water', and on D. barbata , representing a 'turbid-water' species.
2. In contrast to predictions based on seasonal occurrence patterns, D. pulex had a higher intrinsic rate of increase ( r _c)s over most of the turbidity range than D. barbata. Consistent differences in life history between the two species were found, but life history characteristics were rather insensitive to turbidity levels. Although turbidity per se appears to have little direct effect on life history parameters, it could influence the seasonal succession of these two species by interacting with other factors.
3. It is suggested that visual predation by fish rather than turbidity per se probably influenced the seasonality of Daphnia species. During the warmer months, selective removal of D. pulex by visually foraging fishes may allow D. barbata to gain dominance. Effects of temperature and nutrition also merit further study.     

Habitat selection in two species of aquatic hyphomycetes

Two species of aquatic hyphomycetes,Tetracladium marchalianum andTricladium splendens, were isolated from decaying leaves in a stream.T. marchalianum was abundant on alder leaves but absent on beech leaves, which were dominated byT. splendens. It was hypothesized that differences in some chemical key factors in the leaves would account for differences in the distribution of the 2 species. In the experiment designed to test the hypothesis, combinations of sterilized leaves and isolated fungi were used. Differences in growth of FDA active mycelium were related to differences in leaf weight loss;T. splendens decomposed beech leaves andT. marchalianum decomposed alder leaves. Extracellular protease activity corresponded with these trends but there was no detectable protein loss in the leaves. Both fungi showed a nitrogen demand, and hydrolysis of leaf proteins was complemented with absorption of free amino acids and ammonium. High concentrations of free amino acids modified the pattern for habitat selection so thatT. splendens grew substantially on alder leaves andT. marchalianum colonized beech leaves. No protease activity was, however, found fromT. marchalianum on beech leaves, and it is concluded that a more general metabolic inhibition prevents extensive growth of this species on beech leaves. The low natural abundance ofT. splendens on alder leaves, where it may grow well, may be a consequence of a specific protease inhibition and competition from other species.     

Habitat selection as a source of inter‐specific differences in recruitment of two diadromous fish species

• 1 For aquatic species with highly dispersive offspring, the addition of new individuals into an area (recruitment) is a key process in determining local population size so understanding the causes of recruitment variability is critical. While three general causative mechanisms have been identified (the supply of individuals, habitat selection and mortality), we have a limited understanding of how variation in each is generated, and the consequences this may have for the spatial and temporal distribution of recruits.
• 2 We examined whether active habitat selection during settlement could be the cause of variability in populations of two diadromous fish species using a field survey and laboratory‐based choice experiments. If larval behaviour is important, we predicted there would be inter‐specific differences in abundance between sites during the survey, and that larvae would prefer water collected from sites with higher conspecific abundances during the experiments.
• 3 During the field survey, significant differences were detected between two rivers (the Cumberland and Grey), with one species (Galaxias maculatus) found in higher abundances at one site (the Cumberland River) while comparable numbers of a closely related species (Galaxias brevipinnis) were caught at both sites. Laboratory choice experiments were conducted to determine whether larval preferences during settlement could be the cause of these differences. G. maculatus larvae showed a preference for freshwater over saltwater, indicating that the fish may be responding to reduced salinities around river mouths during settlement. The results of a second experiment were consistent with the notion that larval preferences could be the mechanism driving differences in the populations of the two rivers, with G. maculatus preferring water collected from the Cumberland River while G. brevipinnis did not prefer water from either river.
• 4 These results demonstrate that active habitat selection may be important in establishing spatial patterns of larvae at settlement, and that multiple cues are likely to be involved. This study also demonstrates that the behaviours exhibited by individuals can strongly influence the structure and dynamics of populations of aquatic species with complex life cycles.

     

Correlations between genet architecture and some life history features in three species of Solidago

Summary Members of the genus Solidago are among the most widely studied model systems in plant population biology. A comparative study of Solidago canadensis, S. altissima, and S. gigantea in an experimental garden showed that the three species had different patterns of shoot growth and development, leaf morphology and physiology, and biomass allocation at harvest. These differences were also found in the field. Contrary to some current taxonomic usage, our results show that S. canadensis should ecologically be treated as a separate taxon distinct from S. altissima, and that the latter may be grouped together with S. gigantea. Many of the biological differences between S. canadensis and the other two taxa, such as differential investment into sexual reproduction versus clonal growth, may be explained by differences in genet architecture. These architectures concern high compared to lower within-genet shoot density resulting from differences in rhizome lengths among the taxa (shorter in S. canadensis than in S. altissima and S. gigantea).     

A comparison between desert and Mediterranean antlion populations: differences in life history and morphology

We performed a transplant experiment to compare the life histories and morphologies of five geographically representative antlion Myrmeleon hyalinus populations along a sharp climatic gradient, from a Mediterranean climate in Israel's north to a desert climate in the south. Larvae were raised in two environmental chambers simulating Mediterranean and desert climates to investigate the extent to which the different populations exhibit phenotypic plasticity. Along the north-to-south climatic gradient, we observed a gradient in body mass prior to pupation and in pupation rate. Mediterranean populations suffered higher mortality rate when exposed to desert conditions, whereas the mortality rate of desert populations was consistent between Mediterranean and desert conditions. Our results regarding body mass, pupation rate and mortality rate suggest that Mediterranean populations had a more flexible response compared with desert populations. An analysis of digital photographs was used to measure population morphological differences, which were usually indicative of a decrease in trait size along the north-to-south gradient. We show how climatic gradients translate into phenotypic differences in an antlion population and provide a morphometric tool to distinguish between instar stages.     

Habitat preference and habitat exploration in two species of satyrine butterflies

We compared the habitat preference and the mobility of different populations of primarily forest living, satyrine butterflies by observing them in a manipulated environment, containing different habitat types inside a large outdoor cage. The cage was 30 m long and divided into three parts. Each end of the cage contained a shady habitat, made to be similar to the floor of a forest with sunlit spots. In between these shady parts, there was a 14 m long open part, like a glade or a meadow. We performed two studies in the cage. In the first study, we compared a population of a species with very restricted distribution in Sweden, Lopinga achine , and a population of a widely distributed and expanding species, Pararge aegeria . We found that the two species had similar habitat preferences in the cage, but that L. achine had a lower rate of dispersal from one shady part of the cage to the other. In the second study, we compared two populations of P. aegeria , a Swedish forest living population and a Madeiran population inhabiting a fairly open habitat. We found that, although individuals of the Swedish population avoided staying in the open, middle part of the cage, they dispersed between the shady parts of the cage at a higher rate than individuals of the Madeiran population. We argue that studies of the kind we performed can serve the purpose of testing hypotheses about habitat preference and mobility that derive from other field work or from information about distribution patterns.     

The ontogeny of bone growth in two species of dormice: Reconstructing life history traits

Though bone histology has become a powerful tool to reconstruct life history strategies and physiology in living and extinct reptiles and amphibians, it is of limited use in mammals. Dormice (Myoxidae) are good candidates for assessing the relation between bone microstructure and life history due to their long life span, marked physiological cycles and negligible bone remodelling. We carried out the most comprehensive study so far analyzing 16 wild individuals of unknown age belonging to two different species of dormice, Glis glis and Eliomys quercinus. Our study shows a high degree of consistency in the number of resting lines present in bones of the same individual, with femora providing the most accurate age estimations. Moreover, the presence of a single LAG in some juveniles allows discerning between offspring from different reproductive events (early or late litters).     

Habitat selection and potential fitness consequences of two early‐successional species with differing life‐history strategies

Habitat selection and its relationship to fitness is a fundamental concept in ecology, but the mechanisms driving this connection are complex and difficult to detect. Despite the difficulties in understanding such intricate relationships, it is imperative that we study habitat selection and its relationship with fitness. We compared habitat selection of least terns (Sternula antillarum) and piping plovers (Charadrius melodus) on the Missouri River (2012–2014) to examine the consequences of those choices on nest and chick survival. We hypothesized that plovers and terns would select habitat that minimized the chance of flooding and predation of eggs, chicks, and adults, but that plovers would also select habitat that would provide foraging habitat for their chicks. We developed an integrated habitat selection model that assessed selection across multiple scales (sandbar and nest scales) and directly modeled the effect of selection on nest and chick survival. In general, the species selected habitat in keeping with our hypotheses, such that predation and flooding, in particular, may have been reduced. Sandbar selection had either a negative or no appreciable effect on nest survival for both species across years. Nest‐site selection in 2012 had a generally positive effect on nest survival and chick survival for both terns and plovers, and this trended toward a negative effect by 2014. This result suggested that early selection decisions appeared to be adaptive, but we speculate that relatively high site fidelity and habitat degradation led to reduced benefit over time. Our results highlight the complex nature of habitat selection and its relationship to fitness.     

Divergence in parental care, habitat selection and larval life history between two species of Peruvian poison frogs: an experimental analysis

Changes in the nature of the ecological resources exploited by a species can lead to the evolution of novel suites of behaviours. We identified a case in which the transition from large pool use to the use of very small breeding pools in neotropical poison frogs (family Dendrobatidae) is associated with the evolution of a suite of behaviours, including biparental care (from uniparental care) and social monogamy (from promiscuity). We manipulated breeding pool size in order to demonstrate experimentally that breeding habitat selection strategy has evolved in concert with changes in parental care and mating system. We also manipulated intra- and interspecific larval interactions to demonstrate that larval adaptation to the use of very small pools for breeding affected the evolution of larval competition and cannibalism. Our results illustrate the intimate connection between breeding pool ecology, parental care and mating strategies in Peruvian poison frogs.     

Comparative life history of female mosquito fish,Gambusia affinis,in tidal freshwater and oligohaline habitats

Synopsis Female Gambusia affinis were collected from low salinity/near-neutral pH and tidal freshwater/low pH localities to document life history variation between these two habitats. Mosquito fish were 2.7 times more abundant in low salinity/near-neutral pH (2.37 ± 0.72 ppt; pH = 5.73 ± 0.11) than in tidal freshwater/low pH (0.27 ± 0.19 ppt; pH = 4.46 ± 0.18) habitats in Old Fort Bayou, a black-water tidal river of the Biloxi Bay estuary, Mississippi. Fish were common in both areas from June 1985 through February 1986. There were no significant differences between habitats in the length-weight relationships during the reproductive season with the exception of February. However, there were significant differences in life histories, although the areas were only 4 km apart. Ovarian recrudescence was observed in fish from both areas in February, but ovaries of low salinity fish were more developed than ovaries of freshwater fish. All fish from both areas had regressed ovaries by late September. The monthly slopes of the brood size vs. standard length regressions were significantly different between areas throughout the reproductive season with the exception of June. Although freshwater fish produced heavier tail-free embryos, fish from low salinity had significantly higher GSI values and brood size throughout the reproductive season. These observations suggest that Gambusia affonis may have a greater reproductive effort in low salinity/near-neutral pH environments than in freshwater/low pH habitats.     

Body shape and differences between species

The variation of body shape among prosimians is reviewed. Special emphasis is placed on the selective advantages, that is the mechanical reasons, to which variants of the locomotor apparatus can be traced back. There are differences found in the cheiridia, but at present they cannot be explained in terms of mechanics; there is nearly no knowledge about the mechanical meaning of their diversity. Myological characteristics of taxa can be explained mechanically, but this has not yet been done. Well known are variations of body proportions. These discriminate higher taxa, and are largely coincident with the often-used locomotor categories. In spite of this, there are only few sound arguments about the real biomechanic value of characteristic proportions for a given locomotor mode. What is known on this field, is reviewed. Progress can be made only, if the mechanical conditions, set by postural behavior and locomotion, are understood completely. The subtle distinctions between lower taxonomic units can normally be identified only on the basis of detailed and quantified analyses of movements on one hand, and of biometrics on the other. In the few cases in which such studies have been made, the differences of morphology fit to the mechanical requirements of locomotion which also differ only in quantitative details.     

Life history differences between two forms of the social spider mite, Stigmaeopsis miscanthi

The two forms of Stigmaeopsis miscanthi (Saito) (called LW and HG) differ in their levels of male-to-male aggression, differ in their diapause attributes, and morphologically in the male leg I armor. Furthermore, a type of reproductive isolation exists between the forms, although some one-way compatibility is maintained. Here we looked for any differences in life history traits between the two forms under experimental conditions. The intrinsic rate of natural increase (r _m ) of the LW form was lower than that of the HG form, the difference seemingly caused by the developmental speed of the latter. Although the developmental speeds of HG under several temperature regimens were significantly higher than those of LW, the low development threshold temperatures of the two forms were almost identical. This study addresses why a significant difference in r _m exists in relation to other behavior and physiological (diapause) adaptations.     

Community stability,complexity and species life history strategies

The essence of the contradiction between traditional ecological complexity-stability hypothesis and recent theoretical results is clarified. The distinction between resilience and resistance is stressed. The possibilities of field verification of May's model are discussed. No satisfactory method for estimation of connectance and mean interaction strength in plant communities has been found. Relation between these parameters and stability in real communities remains an open question. The relation between connectance and stability (resilience) in purely competitive model communities is more complicated than May's rule predicts. The certain value of connectance having been achieved, stability increases with increasing connectance. We assessed the positive relation between species diversity and resistance, and negative relation between species diversity and resilience in plant communities during old-field succession in xeric habitat. But there is no causal relationship between species diversity and both kinds of stability. Resistance and resilience of the plant communities studied were determined primarily by life history strategies of constituent species. The results are interpreted in terms of Grimes' life history strategies and imply the validity of Gleasonian, population-centered explanation of community phenomena.The nomenclature of plants follows F. Ehrendorfer, 1973, Liste der Gefässpflanzen Mitteleuropas, 2. Aufl. G. Fischer, Stuttgart.Acknowledgements. We thank Pavel Kindlmann for helpful discussion. We are also grateful to reviewers for suggesting ways to improve this paper.