Ecology Letters

Valladares, Fernando; Matesanz, Silvia; Guilhaumon, François; Araújo, Miguel B.; Balaguer, Luis; Benito‐Garzón, Marta; Cornwell, Will; Gianoli, Ernesto; Kleunen, Mark; Naya, Daniel E.; Nicotra, Adrienne B.; Poorter, Hendrik; Zavala, Miguel A.; Thuiller, Wilfried

doi: 10.1111/ele.12348pmid: 25205436

Species are the unit of analysis in many global change and conservation biology studies; however, species are not uniform entities but are composed of different, sometimes locally adapted, populations differing in plasticity. We examined how intraspecific variation in thermal niches and phenotypic plasticity will affect species distributions in a warming climate. We first developed a conceptual model linking plasticity and niche breadth, providing five alternative intraspecific scenarios that are consistent with existing literature. Secondly, we used ecological niche‐modeling techniques to quantify the impact of each intraspecific scenario on the distribution of a virtual species across a geographically realistic setting. Finally, we performed an analogous modeling exercise using real data on the climatic niches of different tree provenances. We show that when population differentiation is accounted for and dispersal is restricted, forecasts of species range shifts under climate change are even more pessimistic than those using the conventional assumption of homogeneously high plasticity across a species' range. Suitable population‐level data are not available for most species so identifying general patterns of population differentiation could fill this gap. However, the literature review revealed contrasting patterns among species, urging greater levels of integration among empirical, modeling and theoretical research on intraspecific phenotypic variation.

Lopez Pascua, Laura; Hall, Alex R.; Best, Alex; Morgan, Andrew D.; Boots, Mike; Buckling, Angus; Fukami, Tadashi

doi: 10.1111/ele.12337pmid: 25167763

We still know very little about how the environment influences coevolutionary dynamics. Here, we investigated both theoretically and empirically how nutrient availability affects the relative extent of escalation of resistance and infectivity (arms race dynamic; ARD) and fluctuating selection (fluctuating selection dynamic; FSD) in experimentally coevolving populations of bacteria and viruses. By comparing interactions between clones of bacteria and viruses both within‐ and between‐time points, we show that increasing nutrient availability resulted in coevolution shifting from FSD, with fluctuations in average infectivity and resistance ranges over time, to ARD. Our model shows that range fluctuations with lower nutrient availability can be explained both by elevated costs of resistance (a direct effect of nutrient availability), and reduced benefits of resistance when population sizes of hosts and parasites are lower (an indirect effect). Nutrient availability can therefore predictably and generally affect qualitative coevolutionary dynamics by both direct and indirect (mediated through ecological feedbacks) effects on costs of resistance.

Kaufmann, Joshka; Lenz, Tobias L.; Milinski, Manfred; Eizaguirre, Christophe; Marshall, Dustin

doi: 10.1111/ele.12344pmid: 25168056

Forces shaping an individual's phenotype are complex and include transgenerational effects. Despite low investment into reproduction, a father's environment and phenotype can shape its offspring's phenotype. Whether and when such paternal effects are adaptive, however, remains elusive. Using three‐spined sticklebacks in controlled infection experiments, we show that sperm deficiencies in exposed males compared to their unexposed brothers functionally translated into reduced reproductive success in sperm competition trials. In non‐competitive fertilisations, offspring of exposed males suffered significant costs of reduced hatching success and survival but they reached a higher body condition than their counterparts from unexposed fathers after experimental infection. Interestingly, those benefits of paternal infection did not result from increased resistance but from increased tolerance to the parasite. Altogether, these results demonstrate that parasite resistance and tolerance are shaped by processes involving both genetic and non‐genetic inheritance and suggest a context‐dependent adaptive value of paternal effects.

Hovick, Stephen M.; Whitney, Kenneth D.; Gurevitch, Jessica

doi: 10.1111/ele.12355pmid: 25234578

The hypothesis that interspecific hybridisation promotes invasiveness has received much recent attention, but tests of the hypothesis can suffer from important limitations. Here, we provide the first systematic review of studies experimentally testing the hybridisation‐invasion (H‐I) hypothesis in plants, animals and fungi. We identified 72 hybrid systems for which hybridisation has been putatively associated with invasiveness, weediness or range expansion. Within this group, 15 systems (comprising 34 studies) experimentally tested performance of hybrids vs. their parental species and met our other criteria. Both phylogenetic and non‐phylogenetic meta‐analyses demonstrated that wild hybrids were significantly more fecund and larger than their parental taxa, but did not differ in survival. Resynthesised hybrids (which typically represent earlier generations than do wild hybrids) did not consistently differ from parental species in fecundity, survival or size. Using meta‐regression, we found that fecundity increased (but survival decreased) with generation in resynthesised hybrids, suggesting that natural selection can play an important role in shaping hybrid performance – and thus invasiveness – over time. We conclude that the available evidence supports the H‐I hypothesis, with the caveat that our results are clearly driven by tests in plants, which are more numerous than tests in animals and fungi.

Pillai, Pradeep; Gouhier, Tarik C.; Vollmer, Steven V.; Ostfeld, Richard

doi: 10.1111/ele.12349pmid: 25199498

The persistence of mutualisms in host‐microbial – or holobiont – systems is difficult to explain because microbial mutualists, who bear the costs of providing benefits to their host, are always prone to being competitively displaced by non‐mutualist ‘cheater’ species. This disruptive effect of competition is expected to be particularly strong when the benefits provided by the mutualists entail costs such as reduced competitive ability. Using a metacommunity model, we show that competition between multiple cheaters within the host's microbiome, when combined with the spatial structure of host–microbial interactions, can have a constructive rather than a disruptive effect by allowing the emergence and maintenance of mutualistic microorganisms within the host. These results indicate that many of the microorganisms inhabiting a host's microbiome, including those that would otherwise be considered opportunistic or even potential pathogens, play a cryptic yet critical role in promoting the health and persistence of the holobiont across spatial scales.

Fraterrigo, Jennifer M.; Wagner, Stephanie; Warren, Robert J.; Wiens, John

doi: 10.1111/ele.12352pmid: 25199542

A hierarchical view of niche relations reconciles the scale‐dependent effects of abiotic and biotic processes on species distribution patterns and underlies most current approaches to distribution modeling. A key prediction of this framework is that the effects of biotic interactions will be averaged out at macroscales – an idea termed the Eltonian noise hypothesis (ENH). We test this prediction by quantifying regional variation in local abiotic and biotic niche relations and assess the role of macroclimate in structuring biotic interactions, using a non‐native invasive grass, Microstegium vimineum, in its introduced range. Consistent with hierarchical niche relations and the ENH, macroclimate structures local biotic interactions, while local abiotic relations are regionally conserved. Biotic interactions suppress M. vimineum in drier climates but have little effect in wetter climates. A similar approach could be used to identify the macroclimatic conditions under which biotic interactions affect the accuracy of local predictions of species distributions.

Lawson, Adam M.; Weir, Jason T.; Wiens, John

doi: 10.1111/ele.12346pmid: 25168260

Despite the importance of divergent selection to the speed of evolution, it remains poorly understood if divergent selection is more prevalent in the tropics (where species richness is highest), or at high latitudes (where paleoclimate change has been most intense). We tested whether the rate of climatic‐niche evolution – one proxy for divergent selection – varies with latitude for 111 pairs of bird species. Using Brownian motion and Ornsetin–Ulhenbeck models, we show that evolutionary rates along two important axes of the climatic‐niche – temperature and seasonality – have been faster at higher latitudes. We then tested whether divergence of the climatic‐niche was associated with evolution in traits important in ecological differentiation (body mass) and reproductive isolation (song), and found that climatic divergence is associated with faster rates in both measures. These results highlight the importance of climate‐mediated divergent selection pressures in driving evolutionary divergence and reproductive isolation at high latitudes.

Carvalheiro, Luísa Gigante; Biesmeijer, Jacobus Christiaan; Benadi, Gita; Fründ, Jochen; Stang, Martina; Bartomeus, Ignasi; Kaiser‐Bunbury, Christopher N.; Baude, Mathilde; Gomes, Sofia I. F.; Merckx, Vincent; Baldock, Katherine C. R.; Bennett, Andrew T. D.; Boada, Ruth; Bommarco, Riccardo; Cartar, Ralph; Chacoff, Natacha; Dänhardt, Juliana; Dicks, Lynn V.;

Jorge, Leonardo R.; Prado, Paulo I.; Almeida‐Neto, Mário; Lewinsohn, Thomas M.; Novotny, Vojtech

doi: 10.1111/ele.12347pmid: 25168335

Resource specialisation, although a fundamental component of ecological theory, is employed in disparate ways. Most definitions derive from simple counts of resource species. We build on recent advances in ecophylogenetics and null model analysis to propose a concept of specialisation that comprises affinities among resources as well as their co‐occurrence with consumers. In the distance‐based specialisation index (DSI), specialisation is measured as relatedness (phylogenetic or otherwise) of resources, scaled by the null expectation of random use of locally available resources. Thus, specialists use significantly clustered sets of resources, whereas generalists use over‐dispersed resources. Intermediate species are classed as indiscriminate consumers. The effectiveness of this approach was assessed with differentially restricted null models, applied to a data set of 168 herbivorous insect species and their hosts. Incorporation of plant relatedness and relative abundance greatly improved specialisation measures compared to taxon counts or simpler null models, which overestimate the fraction of specialists, a problem compounded by insufficient sampling effort. This framework disambiguates the concept of specialisation with an explicit measure applicable to any mode of affinity among resource classes, and is also linked to ecological and evolutionary processes. This will enable a more rigorous deployment of ecological specialisation in empirical and theoretical studies.

Segre, Hila; Ron, Ronen; De Malach, Niv; Henkin, Zalmen; Mandel, Micha; Kadmon, Ronen; Vellend, Mark

doi: 10.1111/ele.12343pmid: 25167950

Species diversity has two components – number of species and spatial turnover in species composition (beta‐diversity). Using a field experiment focusing on a system of Mediterranean grasslands, we show that interspecific competition may influence the two components in the same direction or in opposite directions, depending on whether competitive exclusions are deterministic or stochastic. Deterministic exclusions reduce both patch‐scale richness and beta‐diversity, thereby homogenising the community. Stochastic extinctions reduce richness at the patch scale, but increase the differences in species composition among patches. These results indicate that studies of competitive effects on beta diversity may help to distinguish between deterministic and stochastic components of competitive exclusion. Such distinction is crucial for understanding the causal relationship between competition and species diversity, one of the oldest and most fundamental questions in ecology.