Oikos

Evans, Julian C.; Silk, Matthew J.; Boogert, Neeltje J.; Hodgson, David J.

doi: 10.1111/oik.07148pmid: N/A

Social interactions present opportunities for both information and infection to spread through populations. Social learning is often proposed as a key benefit of sociality, while infectious disease spread are proposed as a major cost. Multiple empirical and theoretical studies have demonstrated the importance of social structure for the transmission of either information or harmful pathogens and parasites, but rarely in combination. We provide an overview of relevant empirical studies, discuss differences in the transmission processes of infection and information, and review how these processes have been modelled. Finally, we highlight ways in which animal social network structure and dynamics might mediate the tradeoff between the sharing of information and infection. We reveal how modular social network structures can promote the spread of information and mitigate against the spread of infection relative to other network structures. We discuss how the maintenance of long‐term social bonds, clustering of social contacts in time, and adaptive plasticity in behavioural interactions, all play important roles in influencing the transmission of information and infection. We provide novel hypotheses and suggest new directions for research that quantifies the transmission of information and infection simultaneously across different network structures to help tease apart their influence on the evolution of social behaviour.

Schwarz, Benjamin; Vázquez, Diego P.; CaraDonna, Paul J.; Knight, Tiffany M.; Benadi, Gita; Dormann, Carsten F.; Gauzens, Benoit; Motivans, Elena; Resasco, Julian; Blüthgen, Nico; Burkle, Laura A.; Fang, Qiang; Kaiser‐Bunbury, Christopher N.; Alarcón, Ruben; Bain, Justin A.; Chacoff, Natacha P.; Huang, Shuang‐Quan; LeBuhn, Gretchen; MacLeod, Molly;

Lesser, Justin S.; James, W. Ryan; Stallings, Christopher D.; Wilson, Rachel M.; Nelson, James A.

doi: 10.1111/oik.07026pmid: N/A

The production and transfer of biomass through trophic relationships is a core ecosystem function. The movement of energy through the food web is mediated by organisms operating in their niche space. For generalists, the size of this niche space is inherently plastic and changes in response to available food sources. Therefore, this relationship between ecosystem productivity and niche size is an important determinant of ecosystem function. Competing theories about the nature of this relationship predict that as productivity increases niche size will either increase as species capitalize on a general increase in resource availability or decrease as it becomes viable to focus on preferred production channels. Here, we test these two competing theoretical frameworks using a novel approach to determine trophic niche size using stable isotope analysis and hypervolume metrics. Resource use is quantified in two generalist fish species at three productivity levels in a seagrass ecosystem. Niche size of both species was inversely related to seagrass productivity, consistent with the hypothesis that increasing productivity allows species to focus on a narrower diet. This pattern describes the relationship between ecosystem production and niche size and provides an empirical ecological explanation for the resource maximization behaviors commonly observed in nature.

Ellis, Vincenzo A.; Huang, Xi; Westerdahl, Helena; Jönsson, Jane; Hasselquist, Dennis; Neto, Júlio M.; Nilsson, Jan‐Åke; Nilsson, Johan; Hegemann, Arne; Hellgren, Olof; Bensch, Staffan

doi: 10.1111/oik.07280pmid: N/A

Many hypotheses attempt to explain parasite–host associations, but rarely are they examined together in a single community. For hosts, key traits are the proportion of infected individuals (prevalence) and the diversity of parasites infecting them. A key parasite trait is host specificity, ranging from specialists infecting one or a few closely related species to generalists infecting many species. We tested 10 hypotheses to explain host‐parasite associations; five ‘host‐centric’ (e.g. prevalence is related to host abundance) and five ‘parasite‐centric’ (e.g. parasite abundance is related to host specificity). We analyzed a community of 67 locally transmitted avian haemosporidian parasite lineages (genera Plasmodium, Haemoproteus or Leucocytozoon), sampled from 2726 birds (64 species) in southern Sweden. Among host‐centric hypotheses, Haemoproteus and Leucocytozoon prevalence and Haemoproteus diversity were related to host habitat preferences, whereas there were no relationships with host abundance or body mass. Haemoproteus and Leucocytozoon prevalences were more similar among closely related than among distantly related host species. Haemoproteus prevalence and diversity were lower in host species with few close relatives (‘evolutionarily distinct’ hosts). Among parasite‐centric hypotheses, most lineages, even relative generalists, infected closely related host species more often than expected by chance. However, the host species of Haemoproteus and Leucocytozoon lineages overlapped less among lineages than expected by chance. Specialists did not reach higher prevalences than generalists on single host species. However, the abundance of Haemoproteus lineages was related to host specificity with generalists more common than specialists; this was driven by three closely related generalists. Host specificity of parasites was unrelated to the abundance or evolutionarily distinctiveness of their hosts. Parasite communities are likely structured by many factors and cannot be explained by hypotheses focusing solely on hosts or parasites. However, we found consistent effects of host phylogenetic relationships, plausibly a result of evolutionarily conserved host immune systems limiting parasite distributions.

Tüzün, Nedim; De Block, Marjan; Stoks, Robby

doi: 10.1111/oik.07183pmid: N/A

Intraspecific latitudinal patterns in life history are well documented, yet underlying mechanisms of such patterns are poorly understood. To advance our insights in the evolution of latitudinal differences in two key traits, growth rate and lifespan, we evaluated the potential costs of rapid growth in terms of reduced adult lifespan, and the mediatory role of oxidative stress. We studied latitudinal differentiation in routine and experimentally increased (compensatory) larval growth rates, and in adult lifespan under common garden conditions in low‐ and high‐latitude populations of the damselfly Ischnura elegans. The low‐latitude populations showed not only higher routine growth rates but also a stronger compensatory growth response after a transient food shortage compared to the high‐latitude populations. In contrast with a tradeoff scenario, adults of the faster growing low‐latitude populations lived longer, had higher levels of antioxidant enzymes, and tended to experience lower oxidative damage. Importantly, these latitudinal patterns were largely mirrored at the treatment level, where experimentally induced compensatory growth rates were associated with neither oxidative damage nor shorter adult lifespans. Moreover, individuals with a higher growth rate after the transient food shortage did not have shorter adult lifespans or higher oxidative damage, but instead showed a stronger antioxidant defense. Our data indicate that an overcompensatory, hormetic response in antioxidant defense, potentially induced by the higher routine growth rates, resulting in less oxidative damage may underlie these unexpected growth‐lifespan patterns. Our results highlight the added value of incorporating oxidative stress physiology, and the need to consider multivariate tradeoffs in which animals optimize multiple traits, when studying life‐history evolution.

Croy, Jordan R.; Meyerson, Laura A.; Allen, Warwick J.; Bhattarai, Ganesh P.; Cronin, James T.

doi: 10.1111/oik.07260pmid: N/A

Herbivores play a critical role in plant invasions either by facilitating or inhibiting species establishment and spread. However, relatively few studies with invasive plant species have focused on the role of plant tolerance and how it varies geographically to influence invasion success. We conducted a common garden study using two lineages (native and invasive) of the grass Phragmites australis that are prevalent in North American wetlands. Using 31 populations collected across a broad geographic range, we tested five predictions: 1) the invasive lineage is more tolerant to simulated folivory than the native lineage, 2) tolerance to herbivory decreases with increasing latitude of origin of the populations, 3) estimates of tolerance are correlated with putative tolerance traits and plasticity in those traits, 4) a tradeoff exists between tolerance and resistance to herbivory and 5) tolerance has a fitness cost. Response to folivory varied substantially among populations of P. australis, ranging from intolerance to overcompensation. Our model selection procedure deemed lineage to be an important predictor of tolerance but, contrary to our prediction, the native lineage was 19% more tolerant to folivory than the invasive lineage. Tolerance for both lineages exhibited a u‐shaped relationship with latitude. A tolerance–resistance tradeoff was evident within the invasive but not the native lineage. Also, tolerance was positively correlated with belowground biomass allocation, leaf silica concentrations, specific leaf area and plasticity in stem density, and negatively correlated with the relative growth rate of the population and plasticity in putative resistance traits. Lastly, although we did not detect costs of tolerance, our results highlight that fast growth rates can maintain high fitness in the presence of herbivory. Herbivory and plant defense strategies for P. australis lineages in North America exhibit complex biogeographic patterns that cause substantial heterogeneity in enemy release and biotic resistance and, consequently, invasion success.

van Zuijlen, Kristel; Roos, Ruben E.; Klanderud, Kari; Lang, Simone I.; Wardle, David A.; Asplund, Johan

doi: 10.1111/oik.07257pmid: N/A

Lichens and bryophytes are abundant primary producers in high latitude and high elevation ecosystems, and they play an important role in ecosystem processes such as decomposition and nutrient cycling. Despite their importance, little is known about the decomposability of lichens and bryophytes either among or within species, at the whole community level, or how this decomposability is affected by their functional traits. Here, we studied decomposability of lichens and bryophytes at the community‐level and individual species‐level (using 21 species and genera) collected from an elevational gradient in alpine Norway. In order to isolate the elevation effect on litter quality, we used a standardized laboratory bioassay to measure decomposability. In contrast to our expectations, we found that community‐level decomposability of lichens and bryophytes increased with elevation and thus decreasing temperature. In contrast, phosphorus release from the litter decreased with elevation while nitrogen release was unresponsive. Decomposability was explained by nutrient concentrations, litter pH and primary producer group identity (lichens versus bryophytes) at both the individual species and community levels. Species turnover (changes in species composition and abundance) was the main driver of decomposability across elevation at the community level, despite some of the traits explaining decomposability showing high intraspecific variability. Our study highlights the importance of among‐species variation in determining lichen and bryophyte decomposability. Further, the higher decomposability that we found for higher elevations suggests that global warming might result in a shift towards slower decomposable lichen and bryophyte species.

CaraDonna, Paul J.; Waser, Nickolas M.

doi: 10.1111/oik.07526pmid: N/A

Ecological communities consist of species that are joined in complex networks of interspecific interaction. These interactions often form and dissolve rapidly, but this temporal variation is not well integrated into our understanding of the causes and consequences of network structure. If interspecific interactions exhibit temporal flexibility across time periods over which organisms co‐occur, then the emergent structure of the corresponding network may also be flexible, something that a temporally‐static perspective will miss. Here, we use an empirical plant–pollinator system to examine short‐term (week‐to‐week) flexibility in network structure (connectance, nestedness and specialization) and in the individual species interactions that contribute to that structure across three summer growing seasons in a subalpine ecosystem. We then compared the properties of weekly networks to the properties of cumulative networks that aggregate field observations over each full summer season. As a test of the potential robustness of networks to perturbation, we also simulated the random loss of species from weekly networks. A week‐to‐week view reveals considerable flexibility in the interactions of individual species and their contributions to network structure. For example, species that would be considered relatively generalized across their entire activity period may be much more specialized at certain times, and at no point as generalized as the cumulative network may suggest. Furthermore, a week‐to‐week view reveals corresponding flexibility in network structure and potential robustness throughout each summer growing season. We conclude that short‐term flexibility in species interactions leads to short‐term variation in network properties, and that a cumulative, season‐long perspective may miss important aspects of the way in which species interact, with implications for understanding their ecology, evolution and conservation.

Brunbjerg, Ane Kirstine; Bruun, Hans Henrik; Dalby, Lars; Classen, Aimée T.; Fløjgaard, Camilla; Frøslev, Tobias G.; Pryds Hansen, Oskar Liset; Høye, Toke Thomas; Moeslund, Jesper Erenskjold; Svenning, Jens‐Christian; Ejrnæs, Rasmus

doi: 10.1111/oik.07145pmid: N/A

Amidst the global biodiversity crisis, identifying general principles for variation of biodiversity remains a key challenge. Scientific consensus is limited to a few macroecological rules, such as species richness increasing with area, which provide limited guidance for conservation. In fact, few agreed ecological principles apply at the scale of sites or reserve management, partly because most community‐level studies are restricted to single habitat types and species groups. We used the recently proposed ecospace framework and a comprehensive data set for aggregating environmental variation to predict multi‐taxon diversity. We studied richness of plants, fungi and arthropods in 130 sites representing the major terrestrial habitat types in Denmark. We found the abiotic environment (ecospace position) to be pivotal for the richness of primary producers (vascular plants, mosses and lichens) and, more surprisingly, little support for ecospace continuity as a driver. A peak in richness at intermediate productivity adds new empirical evidence to a long‐standing debate over biodiversity responses to productivity. Finally, we discovered a dominant and positive response of fungi and insect richness to organic matter accumulation and diversification (ecospace expansion). Two simple models of producer and consumer richness accounted for 77% of the variation in multi‐taxon species richness suggesting a significant potential for generalization beyond individual species responses. Our study widens the traditional conservation focus on vegetation and vertebrate populations unravelling the importance of diversification of carbon resources for diverse heterotrophs, such as fungi and insects.

Herberich, Maximiliane Marion; Gayler, Sebastian; Anand, Madhur; Tielbörger, Katja

doi: 10.1111/oik.07073pmid: N/A

A pertinent debate in plant ecology centers around the generality of the self‐thinning rule. However, studies focused on highly simplified settings such as even‐aged monospecific populations or optimal conditions. This neglects the fact that most natural communities, to which the classical self‐thinning slope is often applied, are age‐structured, composed of multiple species and exposed to various types of abiotic stress. With the help of an individual‐based model, we relax these simplified assumptions and systematically test for changes in the biomass–density relationships of uneven‐aged, functionally diverse plant communities across a complete stress gradient, using excessive to insufficient soil water as a case study. We show that frequent recruitment, which resulted in an uneven‐aged community, and stress intensity caused predictable changes in the entire biomass–density trajectory. Increasing stress resulted in steeper (more negative) slopes and increased the intercept in the classical self‐thinning section irrespective of excessive or insufficient soil water as a stress type. Recruitment steepened the slope, too and enabled a novel section in the biomass–density trajectory. This novel section represented a quasi‐steady state of the density‐dependent dynamics of new generations which occurred locally within patches of recruitment. At the community level, the slope of the biomass–density relationship at quasi‐steady state had a significantly flatter slope of −1.1 under optimal soil water conditions. Functional diversity showed little impact on density‐dependent mortality. Namely, it resulted in an earlier onset of mortality but not in changes in the values of the slope and intercept. We conclude that the classical −3/2 slope is not useful to describe the biomass–density relationship in natural and semi‐natural plant communities. The magnitude and direction of variation in the slope are related to the age‐structure and abiotic stress intensity in the plant community.