bluuebunny/crossref_metadata_2025 huggingface dataset:
Relaxed circadian rhythm in zooplankton along a latitudinal gradient
Authors: Hansson Lars‐Anders , Becares Eloy , Fernández‐Aláez Margarita , Fernández‐Aláez Camino , Kairesalo Timo , Rosa Miracle Maria , Romo Susana , Stephen Deborah , Vakkilainen Kirsi , Van De Bund Wouter , Van Donk Ellen , Balayla David , Moss Brian
Published: December 2007

To test whether aquatic invertebrates are able to adjust their diel migratory cycle to different day length and presence of predators, we performed standardized enclosure experiments in shallow lakes at four different latitudes from southern Spain, with strong night–day cycles, to Finland where daylight is almost continuous during summer. We show here that nearly continuous daylight at high latitudes causes a relaxation in diel migratory behaviour in zooplankton irrespective of predation risk. At lower latitudes, however, similar conditions lead to pronounced diel rhythms in migration. Hence, zooplankton may show local behavioural adaptations in their circadian rhythm. They are also able to make risk assessments as to whether diel migration is beneficial or not, manifested in a lack of diel migration at near constant daylight, irrespective of predator presence. Our results provide an additional explanation to previous knowledge regarding diel migrations among aquatic invertebrates by showing that both physical (light) and biological (predation) factors may affect the migratory behaviour.
Above‐ and belowground insect herbivores differentially affect soil nematode communities in species‐rich plant communities
Authors: De Deyn Gerlinde B. , Van Ruijven Jasper , Raaijmakers Ciska E. , De Ruiter Peter C. , Van Der Putten Wim H.
Published: December 2007

Interactions between above‐ and belowground invertebrate herbivores alter plant diversity, however, little is known on how these effects may influence higher trophic level organisms belowground. Here we explore whether above‐ and belowground invertebrate herbivores which alter plant community diversity and biomass, in turn affect soil nematode communities. We test the hypotheses that insect herbivores 1) alter soil nematode diversity, 2) stimulate bacterial‐feeding and 3) reduce plant‐feeding nematode abundances. In a full factorial outdoor mesocosm experiment we introduced grasshoppers (aboveground herbivores), wireworms (belowground herbivores) and a diverse soil nematode community to species‐rich model plant communities. After two years, insect herbivore effects on nematode diversity and on abundance of herbivorous, bacterivorous, fungivorous and omni‐carnivorous nematodes were evaluated in relation to plant community composition.

Wireworms did not affect nematode diversity despite enhanced plant diversity, while grasshoppers, which did not affect plant diversity, reduced nematode diversity. Although grasshoppers and wireworms caused contrasting shifts in plant species dominance, they did not affect abundances of decomposer nematodes at any trophic level. Primary consumer nematodes were, however, strongly promoted by wireworms, while community root biomass was not altered by the insect herbivores. Overall, interaction effects of wireworms and grasshoppers on the soil nematodes were not observed, and we found no support for bottom‐up control of the nematodes. However, our results show that above‐ and belowground insect herbivores may facilitate root‐feeding rather than decomposer nematodes and that this facilitation appears to be driven by shifts in plant species composition. Moreover, the addition of nematodes strongly suppressed shoot biomass of several forb species and reduced grasshopper abundance. Thus, our results suggest that nematode feedback effects on plant community composition, due to plant and herbivore parasitism, may strongly depend on the presence of insect herbivores.
Habitat predicts reproductive superfetation and body shape in the livebearing fish Poeciliopsis turrubarensis
Authors: Jaime Zúñiga‐Vega J. , N. Reznick David , B. Johnson Jerald
Published: December 2007

Superfetation, the ability of females to simultaneously carry more than one brood at different developmental stages, is an unusual reproductive strategy that has independently evolved several times in the livebearing fish family Poeciliidae. Why this strategy has evolved remains uncertain. One hypothesis is that superfetation is a response to selective pressures that constrain the physical space within a female in which her offspring can develop. This hypothesis is reasonable, because superfetation should reduce the total volume needed to house developing embryos – that is, fewer large, fully developed embryos will be held by a superfetating female (with several broods at different developmental stages) than a non‐superfetating female (where all embryos reach a fully developed stage at the same time).

In this study, we explore this ‘morphological constraint’ hypothesis of superfetation by examining the livebearing fish, Poeciliopsis turrubarensis. We found that populations vary markedly in degree of superfetation, with individuals carrying from two to four distinct broods across different geographic areas. These populations also occupy a range of habitat types: some populations occur in slow moving coastal rivers near the ocean, while other populations occur far inland in fast moving waters that drain steep mountain environments. In comparing populations from these two types of environments, we find a strong association between stream habitat type and the degree of superfetation within populations. Fish from inland populations have higher levels of superfetation than their coastal counterparts. In addition, geometric morphometric analysis revealed that inland populations are also more fusiform than fish from coastal locations. Combined, these two lines of evidence support the ‘morphological constraint’ hypothesis, and suggest that the life history strategy of superfetation could be driven by environmental pressures that favor a more streamlined phenotype.
On the relationship between trophic position, body mass and temperature: reformulating the energy limitation hypothesis
Authors: Arim Matías , Bozinovic Francisco , Marquet Pablo A.
Published: December 2007

Understanding the factors that constrain and drive changes in food chain length represents an open challenge in ecology. Although several explanatory hypotheses have been proposed, no synthesis has yet been achieved. The role of body size has been well‐studied in recent years because the hierarchy of trophic connections – in which large animals consume small ones – suggests a positive relationship between trophic position and body size. Empirical evidence, however, supports the existence of both positive and negative associations, and some studies have even reported no significant relationship between trophic position and body size. These results suggest that the relationship may be non‐monotonic and driven by several interacting mechanisms. Here, we analyze the effects of energetic limitations and structural constraints on species’ trophic positions. We show that the trophic position of small‐bodied animals can be limited by their ability to consume large prey, whereas energetic limitations strongly constrain trophic positions for large‐bodied animals, with the intensity of this constraint depending on the amount of energy available to top predators. These differences in limiting mechanisms can account for the observed variability in the association between the trophic position of top predators and size. Furthermore, our derivation makes use of the Metabolic theory of ecology and predicts a negative relationship between temperature and the maximum achievable food chain length, providing a mechanistic foundation for the observed reductions in food chain length with temperature.
A review of similarity between seed bank and standing vegetation across ecosystems
Authors: Hopfensperger Kristine N.
Published: December 2007

The relationship between above and belowground species composition has been researched in forests, grasslands, and wetlands to understand what mechanisms control community composition. I thoroughly reviewed 108 articles published between 1945 and 2006 that summarized and provided specific values on similarities between above and belowground communities to identify common trends among ecosystems. Using Sørenson's index of similarity, I found that standing vegetation and its associated seed bank was the least similar in forest ecosystems, most similar in grasslands, and of intermediate similarity in wetlands. I also discovered that species richness was not related to seed bank – vegetation similarity in any of the three ecosystems. Disturbances were a common mechanism driving community composition in all ecosystems, where similarity decreased with time since disturbance in forest and wetland ecosystems and increased with time since disturbance in grasslands. Knowing the relationships between seed bank and standing vegetation may help conservationists to manage against exotic species, plan for community responses to disturbances, restore diversity, and better understand the resilience of an ecosystem.
Species abundance and asymmetric interaction strength in ecological networks
Authors: Vázquez Diego P. , Melián Carlos J. , Williams Neal M. , Blüthgen Nico , Krasnov Boris R. , Poulin Robert
Published: December 2007

The strength of interactions among species in a network tends to be highly asymmetric. We evaluate the hypothesis that this asymmetry results from the distribution of abundance among species, so that species interactions occur randomly among individuals. We used a database on mutualistic and antagonistic bipartite quantitative interaction networks. We show that across all types of networks asymmetry was correlated with abundance, so that rare species were asymmetrically affected by their abundant partners, while pairs of interacting abundant species tended to exhibit more symmetric, reciprocally strong effects. A null model shows that abundance provides a sufficient explanation of the asymmetry structure in some networks, but suggests the role of additional factors in others. Although not universal, our hypothesis holds for a substantial fraction of networks analyzed here, and should be considered as a null model in all studies aimed at evaluating the ecological and evolutionary consequences of species interactions.
Host density predicts presence of cuckoo parasitism in reed warblers
Authors: Stokke Bård G. , Hafstad Inge , Rudolfsen Geir , Bargain Bruno , Beier Josef , Bigas Campàs David , Dyrcz Andrzej , Honza Marcel , Leisler Bernd , Pap Péter L. , PatapaviČius RiČardas , Procházka Petr , Schulze‐Hagen Karl , Thomas Rob , Moksnes Arne , Pape Møller Anders , Røskaft Eivin , Soler Manuel
Published: December 2007

In some hosts of avian brood parasites, several populations apparently escape parasitism, while others are parasitized. Many migratory specialist brood parasites like common cuckoos,Cuculus canorus, experience a short breeding season, and in order to maintain local parasite populations host densities should be sufficiently high to allow efficient nest search. However, no studies have investigated the possible effect of host density on presence of cuckoo parasitism among populations of a single host species. Here, we investigated possible predictors of common cuckoo parasitism in 16 populations of reed warblers,Acrocephalus scirpaceus, across Europe. In more detail, we quantified the effect of host density, number of host breeding pairs, habitat type, mean distance to nearest cuckoo vantage point, predation rate and latitude on the presence of cuckoo parasitism while controlling for geographical distance among study populations. Host density was a powerful predictor of parasitism. We also found a less pronounced effect of habitat type on occurrence of parasitism, while the other variables did not explain why cuckoos utilize some reed warbler populations and not others. This is the first study focusing on patterns of common cuckoo‐host interactions within a specific host species on a large geographic scale. The results indicate that if host density is below a specific threshold, cuckoo parasitism is absent regardless of the state of other potentially confounding variables.
The role of metacommunity processes in shaping invertebrate rock pool communities along a dispersal gradient
Authors: Vanschoenwinkel Bram , De Vries Chris , Seaman Maitland , Brendonck Luc
Published: December 2007

Explaining the variance of local communities in a spatial‐environmental matrix is one of the core interests of ecology today. Recent progress in metacommunity theory has made a substantial contribution to this field, however good empirical data in support of available theories are still relatively scarce. In this study we sampled a cluster of 36 temporary rock pools four times during one season to assess invertebrate metacommunity structure and dynamics and to search for steering processes and variables. Both Mantel tests and redundancy models indicate that local abiotic factors were dominant over spatial factors in explaining community structure and both were acting independently. Spatial variables were only important for passive dispersers and significantly explained 11% of variation in this community component. Pools connected by temporary overflows hosted more similar communities of passive dispersers than unconnected ones while community dissimilarity significantly increased with inter‐pool distance. A negative curvilinear relation was discovered between taxon richness and isolation in passive dispersers, providing some support for existing theoretical models of Mouquet and Loreau. Of different metacommunity perspectives, a combination of species sorting and mass effects best explains the observed patterns. Additionally, priority effects and monopolization may buffer against the homogenising effects of dispersal and contribute to the distinctness of isolated communities. This is one of the first studies to present evidence for spatial patterns in aquatic communities on such a small spatial scale (a rock ledge of ±9000 m2). Bridging the gap between theory and observed patterns in natural systems is one of the main challenges for future metacommunity research. Small aquatic habitats such as pitcher plants and freshwater rock pools may well have an important role to play as model systems to study ecological processes in a natural spatially explicit environment.
The tradeoff between catch‐up growth and escape speed: variation between habitats in the cost of compensation
Authors: Álvarez David , Metcalfe Neil B.
Published: December 2007

Compensatory growth is the faster‐than‐normal growth that some species exhibit after a period of resource deprivation. Using three‐spined sticklebacks as model species we tested the impact of compensatory growth on subsequent escape performance in populations from diverse habitats. We found clear population differences in the rate of compensatory growth, and strong inter‐habitat differences in the impact that catch‐up growth had on burst swimming performance when measured weeks later. In pond populations growth compensation had little effect on burst swimming, whereas fish from stream populations that exhibited rapid catch‐up growth subsequently had slower escape speeds. Those differences could be explained by the non‐linear nature of the tradeoff curve, suggesting that habitat‐specific selection pressures lead to differences in the importance of burst swimming performance.
Do mountain hare populations cycle?
Authors: Newey Scott , Willebrand Tomas , Haydon Daniel T. , Dahl Fredrik , Aebischer Nicholas J. , Smith Adam A. , Thirgood Simon J.
Published: December 2007

We investigated the occurrence and distribution of multi‐annual cycles in abundance of mountain hare populations across a wide area of their range in northern Europe. We analysed 125 time‐series of mountain hare abundance indexed from hunting bag records and questionnaire responses from Scotland, Sweden, Finland and Switzerland. We also reanalysed 17 previously published time‐series based on hunting bag records and snow track indices from mountain hare populations in Scotland, Norway, Sweden, Finland, Russia and Italy. Autocorrelation analysis showed that 45% of mountain hare populations showed evidence of cycles, characterised by significant negative autocorrelations at half or the whole cycle period. The amplitude and periodicity of cycles varied between and within countries. Time‐series in Scotland were characterised by high‐amplitude weak cycles with a mean periodicity of nine years but with a range of 4–15 years. Norwegian and Swedish time‐series revealed low amplitude weak cycles with a 3–7 year period. Finnish time‐series showed low amplitude cycles with a 4–11 year period. Alpine time‐series were predominantly non‐cyclic, while the limited number of series from Russia showed high amplitude weak cycles with an 8–11 year period. The results reveal that mountain hare populations show a wide range of population dynamics with distinct regional differences in periodicity, amplitude and density dependent structure of cycles. These findings suggest that different factors may limit or regulate mountain hare populations in different regions of Europe thus supporting the results of recent field studies.
Competition and intraguild egg predation among freshwater snails: re‐examining the mechanism of interspecific interactions
Authors: Turner Andrew M. , Turner Rebekah R. , Ray Scott R.
Published: December 2007

Experimental and field studies suggest that freshwater snail species have negative effects on each other's population growth rates. Because snails share similar diets, these interactions have been interpreted as the result of exploitative competition, but they could also result from intraguild predation. Here we present three experiments aimed at testing the hypothesis that interspecific interactions among three species of freshwater gastropod (Helisoma trivolvis, Physa acuta and Stagnicola elodes) are mediated by intraguild egg predation. Foraging trials, conducted in a laboratory, showed that some snails readily prey on eggs, but the extent of egg predation depended on both the identity of the snail predator and the identity of the egg mass. Of the three species considered, Stagnicola had the largest effect on egg mortality and Physa had no effect on egg mortality. Foraging trials also showed that the eggs of Physa were the most vulnerable to predators and that the eggs of Stagnicola were largely invulnerable. A study conducted in large outdoor mesocosms assessed the occurrence of egg mortality in an environment of more extensive spatial scale and complexity. The results largely mirrored those of the laboratory study, with Stagnicola being the most voracious predator and the eggs of Physa being most vulnerable to predation. The reproductive success of Physa and Stagnicola raised in sympatry and allopatry was assessed in a mesocosm study conducted over three months. Recruitment of both species was depressed in sympatry, but patterns of growth in the survivors suggest contrasting mechanisms of suppression: Physa suppressed Stagnicola via exploitative competition, but Stagnicola suppressed Physa via egg predation. These experiments support the hypothesis that freshwater snail assemblages are structured by strong interspecific interactions and that a rich interplay of egg predation and interspecific competition underlie interactions among the members of this guild.
Biomass recycling: a key to efficient foraging by fungal colonies
Authors: Falconer Ruth E. , Bown James L. , White Nia A. , Crawford John W.
Published: December 2007

Using an existing fungal growth model that captures the physiological processes of vegetative growth and development of a fungal colony, and in particular incorporates, for the first time, a recycling of biomass mechanism, we explore the effects of recycling in various environmental contexts. Here we test whether resource density thresholds exist, below which finite colony expansion occurs, in three dimensions based on the number of randomly removed resource sites. We then test the effect of recycling on resource density thresholds. Modelled soil structure, derived from experiments, is combined with the fungal growth model. The effect of recycling on foraging efficiency is investigated for resource distributed homogeneously and heterogeneously throughout the modelled soil structure. The simulated results show that resource density thresholds do exist in three dimensions and that the recycling mechanism decreases the threshold value. Our results indicate that recycling promotes persistence and a recycling mechanism is crucial for those fungi that reside in a resource patchy and limited environment.
The relative role of dispersal and local interactions for alpine plant community diversity under simulated climate warming
Authors: Klanderud Kari , Totland Ørjan
Published: December 2007

Most studies on factors determining diversity are conducted in temperate or warm regions, whereas studies in climatically harsh and low productivity areas, such as alpine regions, are rare. We examined the relative roles of seed availability and different biotic and abiotic factors for the diversity of an alpine plant community in southern Norway. Furthermore, because climate warming is predicted to be an important driver of alpine species diversity, we assessed how the relative impacts of dispersal and local interactions on diversity might change under experimental warming (open top chambers, OTCs).

Addition of seeds from 27 regional species increased community diversity. The establishment of the species was negatively related both to the diversity of the existing system and the cover of the abundant dwarf shrubDryas octopetala. These results show that both species dispersal limitation and local biotic interactions are important factors for alpine plant community diversity. Despite relatively harsh environmental conditions and low productivity, competition from the resident vegetation appeared to have a greater role for species establishment and diversity than facilitation and experimental warming. Higher temperature appeared to increase the negative relationship between resident species diversity and species establishment. This may suggest that climate warming can increase the role of interspecific competition for alpine plant community structure, and thus alter the long‐term effects of biotic interactions on diversity.
Alternative nesting behaviours following colonisation of a novel environment by a passerine bird
Authors: Yeh Pamela J. , Hauber Mark E. , Price Trevor D.
Published: December 2007

When birds settle in new environments, they may encounter different suites of nest‐predators, resulting in strong selection to nest in novel locations. An important axis of variation is in height of nest placement, because off‐ground nests are likely to be subject to different predation pressures than on‐ground nests. In their native habitats, i.e. temperate montane forest, dark‐eyed juncosJunco hyemalispredominantly nest on the ground. A population of juncos became established on the urban campus of the Univ. of California at San Diego in the early 1980s, and now has a relatively high frequency (∼20%) of off‐ground nests. Off‐ground nesting is associated with strong fitness benefits: based on returns from 579 nests, an egg laid off the ground has ∼80% higher chance of producing a recruit to the next generation than one laid on the ground. In addition, some nests were occasionally re‐used by ∼10% of females and off‐ground nests were more likely to be re‐used. Many females that bred off‐ground also built an on‐ground nests and we did not detect an association in nest site positions of mothers and daughters, implying low heritability of this novel nest placement trait. By contrast, certain territories consistently had on‐ground nests irrespective of the identity of the breeding female. We suggest that a limitation of suitable off‐ground nest sites for a species predominantly adapted to on‐ground nesting greatly slows the rate of evolution of this trait.
Competition and community structure in diurnal arboreal geckos (genusPhelsuma) in the Indian Ocean
Authors: Harmon Luke J. , Harmon Lisa L. , Jones Carl G.
Published: December 2007

In this study, we investigate community structure in day geckos (genusPhelsuma) in the Indian Ocean. Much of what we know about communities of diurnal arboreal lizards comes from studies of CaribbeanAnolis.Phelsumain the Indian Ocean are ecologically similar toAnolisbut not closely related. Using field observations and an experiment, we test three hypotheses forPhelsumacommunities, all derived from work onAnolis: (1)Phelsumaspecies richness will be correlated with the diversity of available perches, (2) sympatric species will partition their habitat use, shifting their habitat use depending on which other species ofPhelsumaare present, and (3) experimentally removing individuals of one species will lead to changes in the microhabitat use and/or abundance of sympatric congeners. We find support for all three hypotheses. We also describe some unique aspects ofPhelsumacommunities, such as partitioning of palm vs. non‐palm trees. This study identifies some potentially general features of diurnal arboreal lizard communities, and suggests that some aspects of community assembly might be repeatable.
Direct and indirect effects of habitat area and matrix composition on species interactions among flower‐visiting insects
Authors: Diekötter Tim , Haynes Kyle J. , Mazeffa Doug , Crist Thomas O.
Published: December 2007

Traditionally, ecologists have focused on direct effects of habitat area and arrangement on individual species or pairwise species interactions. Indirect effects of habitat heterogeneity on multiple interacting species are often neglected or lack experimental support. In a factorial field experiment, we explored the direct and indirect effects of habitat area, fragmentation, and matrix composition on a community of flower‐visiting insects in red clover. Habitat area, fragmentation, and density of inflorescences of red clover all influenced the insect pollinators and, in turn, the production of clover seeds. The strongest direct effect was on pollinator visitation, which was substantially higher in small clover patches surrounded by bare‐ground than in larger patches embedded within grass. Structural equation modeling indicated that the observed matrix‐dependent changes in pollinator visitation propagated across a tri‐trophic system: higher visitation rates positively correlated with a higher seed set, which in turn was positively correlated with abundances of seed predators and their parasitoids. Therefore, this study suggests that habitat area and matrix composition can strongly influence the structure of species interaction webs through indirect effects, and also emphasizes that these effects can be propagated through mutualistic as well as trophic interactions.
Ontogeny, diet shifts, and nutrient stoichiometry in fish
Authors: Pilati Alberto , Vanni Michael J.
Published: December 2007

Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient composition and excretion rates. We quantified ontogenetic variation in stoichiometry and diet in gizzard shad, Dorosoma cepedianum, an omnivorous fish with a pronounced ontogenetic diet shift; and zebrafish, Danio rerio, grown in the lab with a constant diet. In both species, body stoichiometry varied considerably along the life cycle. Larval gizzard shad and zebrafish had higher molar C:P and N:P ratios than larger fish. Variation in body nutrient ratios was driven mainly by body P, which increased with size. Gizzard shad body calcium content was highly correlated with P content, indicating that ontogenetic P variation is associated with bone formation. Similar trends in body stoichiometry of zebrafish, grown under constant diet in the laboratory, suggest that ontogeny (e.g. bone formation) and not diet shift is the main factor affecting fish body stoichiometry in larval and juvenile stages. The N:P ratio of nutrient excretion also varied ontogenetically in gizzard shad, but the decline from larvae to juveniles appears to be largely associated with variation in the N:P of alternative food resources (zooplankton vs detritus) rather than by fish body N:P. Furthermore, the N:P ratio of larval gizzard shad excretion appears to be driven more by the N:P ratio at which individuals allocate nutrients to growth, more so than static body N:P, further illustrating the need to consider ontogenetic variation. Our results thus show that fish exhibit considerable ontogenetic variation in body stoichiometry, driven by an inherent increase in the relative allocation of P to bones, whereas ontogenetic variation in excretion N:P ratio of gizzard shad is driven more by variation in food N:P than by body N:P.
Colonization sequence influences selection and complementarity effects on biomass production in experimental algal microcosms
Authors: Zhang Quan‐Guo , Zhang Da‐Yong
Published: December 2007

Species extinction and immigration are both common in natural communities and the sequence with which species are lost from or added to communities may be crucial to community structure. We experimentally addressed this issue by growing six green algal species in monocultures and all possible two‐species mixtures, with two colonization sequences for each mixture. Both convergence and divergence in community structure were observed. The compositions containing particularly productive species were more likely to converge, while those comprising of species with similar monoculture yields were more likely to diverge. The species mixtures with high‐yielding initial and low‐yielding invading species produced more biomass than monocultures, but mixtures with the opposite assembly order produced only the same level of biomass as monocultures did. To address the diversity–ecosystem functioning issue, we estimate complementarity effect by relative yield total (RYT) and selection effect by the correlation between species’ monoculture yields and their relative yields in mixtures, respectively. We found overall negative complementarity and positive selection effect in mixtures with high‐yielding species as initial colonizers, but positive complementarity and negative selection effect in mixtures with low‐yielding initial species. Nonetheless, because we used only up to two species in each microcosm, our results are limited in addressing the relationship between species diversity and ecosystem functioning. Future research should study the effects of immigration history with many more species involved in community assembly.
Differences in morphology, performance and behaviour between recently diverged populations of Podarcis sicula mirror differences in predation pressure
Authors: Vervust Bart , Grbac Irena , Van Damme Raoul
Published: December 2007

We investigated the possible role of variation in predation pressure in the phenotypic divergence of two island populations of the Italian wall lizard, Podarcis sicula. In 1971, ten adult specimens from the island of Pod Kopište (Adriatic Sea, Croatia) were transported to the island of Pod Mrčaru, 3.5 km east, where they founded a new population. Although the two islands resemble each other in general physiognomy (size, elevation, microclimate) and in the absence of terrestrial predators, lizards from the newly established population are now on average larger and have shorter hind limbs. They also exhibit lower maximal sprint speed as measured on a racetrack, and fatigue faster when chased in a torus track. In the field, lizards from the original population of Pod Kopište respond to a simulated predatory attack by fleeing at larger approach distances and by running further from the predator than lizards from Pod Mrčaru. These changes in morphology, behaviour and performance may result from the relaxed predation intensity on the latter island. Our analysis of the structural features of the microhabitats suggests that the vegetation on Pod Mrčaru offers more protection to lizards. Also, plasticine models of lizards, laid out on the islands, less often exhibited signs of being attacked by birds on Pod Mrčaru than on Pod Kopište. Our findings provide an example of how changes in (possibly a single) environmental factor may simultaneously produce responses in behaviour, morphology and whole‐animal physiology, and this on a surprisingly small spatial and temporal scale.
Effects of phenotypic complementarity and phylogeny on the nested structure of mutualistic networks
Authors: Rezende Enrico L. , Jordano Pedro , Bascompte Jordi
Published: December 2007

Recent studies have started to unravel the structure of mutualistic networks, although few functional explanations underlying such structure have been explored. We used computer simulations to test whether complementarity between phenotypic traits of plants and animals can explain the pervasive tendency of specialists to interact with proper subsets of species that generalists interact with (nested interactions), and how phylogeny affects such interaction patterns. Simultaneously, we assessed whether complementarity and phylogenetic structure were associated with patterns of interaction in a real mutualistic community. Simulation results support that highly nested networks can emerge from phenotypic complementarity, particularly when several traits are involved. The hierarchical structure of phylogenetic relations can also contribute to increased nestedness because traits determining complementarity are then inherited in a correlated fashion. Phylogenetic effects on resulting generalization levels are often low, but can be detected. Results from the empirical network support a relevant role of complementarity and phylogenetic history on interaction patterns. Our results demonstrate that these factors can contribute to nestedness, which emphasize the necessity of considering evolutionary mechanisms in studies of community structure.
Which species will succesfully track climate change? The influence of intraspecific competition and density dependent dispersal on range shifting dynamics
Authors: Best A. S. , Johst K. , Münkemüller T. , Travis J. M. J.
Published: December 2007

Understanding the ability of species to shift their geographic range is of considerable importance given the current period of rapid climate change. Furthermore, a greater understanding of the spatial population dynamics underlying range shifting is required to complement the advances made in climate niche modelling. A simulation model is developed which incorporates three key features that have been largely overlooked in studies of range shifting dynamics: the form of intraspecific competition, density dependent dispersal and the transient dynamics of habitat patches. The results show that the exact shape of the response depends critically on both local and patch dynamics. Species whose intraspecific competition is contest based are more vulnerable than those whose competition is scramble based. Contesters are especially sensitive when combined with density dependent dispersal. Species living in patches whose carrying capacity grows slowly are also susceptible to rapid shifts of environmental conditions. A complementary analytic approach further highlights the importance of intraspecific competition.
Coping with an antagonist: the impact of a phytopathogenic fungus on the development and behaviour of two species of alpine leaf beetle
Authors: Röder Gregory , Rahier Martine , Naisbit Russell E.
Published: December 2007

Herbivorous insects and phytopathogenic fungi often share their host plants. This creates a network of direct and indirect interactions, with far‐reaching consequences for the ecology and evolution of all three parties. In the Alps, the leaf beetlesOreina elongataandOreina cacaliae(Coleoptera: Chrysomelidae), and the rust fungusUromyces cacaliae(Uredinales: Pucciniaceae) are found on the same host plant,Adenostyles alliariae(Asterales: Asteraceae). We compare the impact of rust infection on these two closely‐related beetle species, one of which,O. cacaliae,is a specialist onA. alliariae, while the other,O. elongata,moves repeatedly betweenAdenostylesand an alternative host,Cirsium spinosissimum. Larval performance, feeding preference, oviposition choice and dispersal behaviour were studied in field and laboratory experiments. When reared on rust‐infected leaves, larvae of both beetle species had lower growth rates, lower maximum weights and longer development times. Larvae and adults discriminated among diets in feeding trials, showing a preference for discs cut from healthy leaves over those bearing a patch of sporulating rust, those from elsewhere on an infected leaf, and those from an upper leaf on an infected plant. Females of the two species differed in behaviour: inO. cacaliaethey favoured healthy leaves for larviposition, while inO. elongatathey showed no significant preference during oviposition. In the field, larvae and adults of both species dispersed more rapidly when placed on infected host plants. The results demonstrate that rust infection reduces the quality of the plant as a host for bothOreinaspecies, and they combine the ability to detect systemic infection with the evolution of evasive behaviours. For these beetles, competition with a rust clearly increases the difficulty of survival in the harsh conditions of alpine environments, and may have a profound impact on the evolution of their life history traits and host plant use.
Environmental colour intensifies the Moran effect when population dynamics are spatially heterogeneous
Authors: Vasseur David A.
Published: December 2007

Evidence for synchronous fluctuations of spatially separated populations is ubiquitous in the literature, including accounts within and across taxa. Among the few mechanisms explaining this phenomenon is the Moran effect, whereby independent populations are synchronized by spatially correlated environmental disturbances. The body of research on the Moran effect predominantly assumes that environmental disturbances within a local site are serially uncorrelated; that is, successive observations in time at a particular local site are independent. Yet, many environmental variables are known to possess strong temporal autocorrelation – a character which has often been described as ‘colour’. The omission of environmental colour from research on the Moran effect may be due in part to the lack of methods capable of generating sets of time series with a desired colour and spatial correlation. Here I present a novel and simple method designated as ‘phase partnering’ to generate such sets of time series and I investigate the combined impact of spatial correlation and environmental colour on population synchrony in two common models of population dynamics. For linear population dynamics, and for a subset of nonlinear population dynamics, coloured environments intensify the Moran effect when population dynamics are spatially heterogeneous; in coloured environments the spatial correlation between populations more closely mimics the spatial correlation between their respective environments. Given that most environmental variables are coloured, these results imply that the Moran effect may be a far more significant driver of regional‐scale population and interspecific synchrony than is currently believed.
Environmental and senescent related variations in Weddell seal body mass: implications for age‐specific reproductive performance
Authors: Proffitt Kelly M. , Garrott Robert A. , Rotella Jay J. , Wheatley Kathryn E.
Published: December 2007

Recent studies have found age‐specific variations in reproductive performance amongst Weddell seals,Leptonychotes weddellii, and we hypothesized age‐related variations in maternal body mass as a mechanism linking maternal age and the observed patterns of reproductive performance. We evaluated the effects of maternal traits such as age and reproductive experience and the effects of environmental variations on maternal body mass at parturition. Maternal body mass at parturition showed substantial age‐ and environmental‐related variations. Maternal body mass increased with age through the young and middle ages, and evidence of senescent declines in body mass was found amongst the oldest ages. Additionally, body mass at parturition was strongly influenced by environmental variations during the pregnancy period, specifically sea‐ice extent and the state of the El‐Niño Southern Oscillation. Patterns of age‐specific variations in body mass were consistent with age‐specific patterns of offspring survival probability, which supported our hypothesis that changes in body mass link maternal age and reproductive performance in the Weddell seal. Further, environmental conditions during pregnancy may be an important component of Weddell seal reproductive performance.
The ecology and evolution of tooth wear in red deer and moose
Authors: Veiberg Vebjørn , Loe Leif Egil , Mysterud Atle , Solberg Erling J. , Langvatn Rolf , Stenseth Nils Chr.
Published: December 2007

Differences in body size and diet type (browser–grazer continuum) have formed functional traits of ruminants, including tooth design. Grazers and mixed‐feeders eat a more fibrous diet than browsers, which arguably increase tooth wear. Tooth wear has also been suggested to increase with body size. Moreover, for species with large distribution ranges, different populations may be exposed to very different ecological factors affecting diet and thus tooth wear rates. Therefore, evolutionary history and contemporary ecological conditions, both operating through diet, may be important for patterns of tooth wear. Here, we compare inter‐ and intraspecific rates of tooth wear in multiple populations of one large browser (moose Alces alces) and one mixed‐feeder (red deer Cervus elaphus) covering the main distribution range of each species in Norway. We found that the mixed‐feeding red deer wore teeth faster than the larger and browsing moose, suggesting that feeding‐type was more important than body size for patterns of wear. There was substantial spatial variation in tooth wear rates, but the inter‐specific difference in wear was consistent. Molar wear rates, but not incisors wear rates, in the browser were less variable between populations than in the mixed‐feeder. There was no close link between incisor and molar wear rates at the population level. Our findings are consistent with the view that both evolution related to diet type and current ecological conditions (being proxies for within‐species variation in diet quality) are important for patterns of tooth wear.
Longevity in cheetahs: the key to success?
Authors: Pettorelli Nathalie , Durant Sarah M.
Published: December 2007

An understanding of the factors governing reproductive success has fundamental implications for population demography, conservation, selection and adaptation. Although a consistent positive correlation between lifetime reproductive success and longevity has been reported for many iteroparous organisms, few studies have explored how longevity influences annual individual performance. In this study we show (1) that longevity and lifetime reproductive success are positively but not linearly correlated, (2) that short‐lived individuals have higher annual reproductive success, (3) that the generally lower success of the last breeding occasion increased with females’ longevity, and (4) that long‐lived females have higher chances of rearing long‐lived females. We suggest that experience and the increase in the number of reproductive events with longevity are key processes leading to a strong correlation between (1) lifetime reproductive success and longevity and (2) mother and daughter longevities. Our results demonstrate the importance of long term studies that follow multiple generations in gaining a full understanding of the factors affecting reproductive success.
Weak population differentiation in northern European populations of the endangered anadromous clupeid Alosa fallax
Authors: Volk J. , Bekkevold D. , Loeschcke V.
Published: December 2007

Examination of genetic structure among different spawning populations of the endangered twaite shad Alosa fallax showed statistically significant but weak differentiation estimated using nine microsatellite loci. Results point to substantial gene flow among the majority of individual estuary/river spawning locations, and no evidence that habitat disruption has led to increased local genetic drift.
Secondary contact between two divergent lineages of grayling Thymallus in the lower Enisey basin and its taxonomic implications
Authors: Weiss S. , Knizhin I. , Romanov V. , Kopun T.
Published: December 2007

A contact zone between two widespread divergent lineages of grayling Thymallus sp. has been identified in the lower Enisey basin (Khantaiskoye Lake) in north central Siberia (Russia). Sequences of the mitochondrial DNA control region revealed two lineages with 2·6% divergence. Haplotypes from these two lineages clearly fall within two previously described clades, one presumably corresponding to Arctic grayling Thymallus arcticus found throughout the Siberian coastal zone as well as North America, and the other corresponding to grayling found elsewhere in the Enisey basin, including Lake Baikal and its tributaries. Allelic variation at seven microsatellite loci strongly suggests reproductive isolation in sympatry between these two lineages in Khantaiskoye Lake. Integration of these new data with existing knowledge on Thymallus throughout its Siberian range supports a taxonomic revision. The currently recognized sub‐specific lineages of Arctic grayling along the Siberian Arctic coast as well as grayling from North America should probably be regarded as T. arcticus. Arctic grayling, however, are limited to the coastal zone and lower reaches of the Enisey. Most of the Enisey basin, including Lake Baikal and its tributaries are occupied by another taxon, which should be recognized as Thymallus baicalensis. This perspective strictly follows evolutionary principles, eliminates the use of four sub‐specific names and circumvents the illogical mosaic distribution of T. arcticus arcticus, which nevertheless does not represent a monophyletic lineage.
Identification and mapping of genes associated with salt tolerance in tilapia
Authors: Rengmark A. H. , Slettan A. , Lee W. J. , Lie Ø. , Lingaas F.
Published: December 2007

This paper describes the finding of genes displaying differential expression in Nile tilapia (Oreochromis niloticus) adapted to saltwater and discusses their potential involvement in saltwater tolerance. The availability of fresh water is severely limited in many countries; therefore, the use of brackish‐water areas may present an opportunity to expand the tilapia aquaculture industry. Increased knowledge of genes involved in saltwater tolerance will facilitate selection for this trait in tilapia. A set of fish from four different families of Nile tilapia was divided into two freshwater containers, the different families equally represented in the two experimental groups, and salinity was gradually increased in one of them. A differential expression study identified a number of genes expressed differently in saltwater and fresh water. Based on these expression analyses and on a judgement of potential candidate genes probably to be involved in adaptation to changes in salinity, four genes were selected and their levels of expression further analysed by real‐time polymerase chain reaction. The selected genes beta haemoglobin, Ca2+ transporting plasma membrane ATPase, pro‐opiomelanocortin and beta‐actin showed changes in expression. The genes were mapped and assigned to an already existing, high‐resolution linkage map.