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Everything ecology and evolutionary biology

Marc Cadotte
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February 3, 2010
09:38 PM
36 views

The evolution of a symbiont

by Marc Cadotte in The EEB and flow

The evolution of negative interactions seems like a logical consequence of natural selection. Organisms compete for resources or view one another as a resource, thus finding ways to more efficiently find and consume prey. However, to me, the natural selection of symbiotic or mutualistic interactions has never seemed as straight forward (expect maybe the case where one species provides protection for the other, such as in ant-plant mutualisms). A specific example is the rise of nitrogen-fixing plants, who supply nutrients to bacteria called rhizobia capable of converting atmospheric nitrogen into forms, such as ammonia, usable to the plant host. Not only has this symbiosis evolved, but has seemed to evolve in very evolutionarily distinct lineages. The question is, what are the mechanisms allowing for this?In a recent paper, Marchetti and colleagues answer part of the question. They experimentally manipulate a pathogenic bacteria and observe it turning into a symbiont. They transferred a plasmid from the symbiotic nitrogen fixing Cupriavidus taiwanensis into Ralstonia solanacearum and infected Mimosa roots with it. Plasmid transfer among distinct bacteria species is common and referred to horizontal genetic transfer (as opposed to vertical, which is the transfer to daughter cells). The presence of the plasmid caused R. solanacearum to quickly evolve into a root-nodulating symbiont. Two regulatory genes lost function, and this caused R. solanacearum to form nodules and to impregnate Mimosa root cells.This extremely novel experiment reveals how horizontal gene transfer can supply the impetus for rapid evolution from being a pathogen to a symbiont. More importantly it reveals that sometimes just a few steps are required for this transition and how distantly-related bacterial species can acquire symbiotic behaviors.Marchetti, M., Capela, D., Glew, M., Cruveiller, S., Chane-Woon-Ming, B., Gris, C., Timmers, T., Poinsot, V., Gilbert, L., Heeb, P., Médigue, C., Batut, J., & Masson-Boivin, C. (2010). Experimental Evolution of a Plant Pathogen into a Legume Symbiont PLoS Biology, 8 (1) DOI: 10.1371/journal.pbio.1000280... Read more »

Marchetti, M., Capela, D., Glew, M., Cruveiller, S., Chane-Woon-Ming, B., Gris, C., Timmers, T., Poinsot, V., Gilbert, L., Heeb, P.... (2010) Experimental Evolution of a Plant Pathogen into a Legume Symbiont. PLoS Biology, 8(1). DOI: 10.1371/journal.pbio.1000280

January 19, 2010
09:47 PM
52 views

Timing is everything: global warming and the timing of species interactions

by Marc Cadotte in The EEB and flow

While an obvious affect of climate change will be changes in the distributions or range sizes of species, more insidious and likely more consequential will be how species interactions are affected by changes in the timing of growth and reproduction. These changes in an organism's life cycle, or phenology, can create mismatches between an organism's need and resource availability or the readiness of coevolved partners -such as plants and pollinators.In an 'Idea and Perspective' paper in Ecology Letters, Louie Yang and Volker Rudolf set out a new framework to examine the effects of phenological shifts on species interactions. They argue that one cannot understand or predict the fitness consequences of a phenology shift without knowing how interacting species' phenologies are also influenced by environmental changes. The consequences of phenological shifts are changes in fitness, and the question is: how would one go about assessing the fitness effects of phenological changes on interactions? This is where this paper really hits its stride. Yang and Rudolf set out a new conceptual framework for studying the fitness consequences of phenological shifts. They make the case that an experimental approach is required to test the three likely scenarios. The first is that there are no changes in phenology -that is, measuring the fitness levels of the two interacting species under stable conditions. Second, you induce an experimental shift in the timing of one of the species. For example, in a plant-herbivore interaction, germinate the plant earlier and when the herbivore normally has access to the plant, the plant will be older. What are the fitness changes associated with this shift? Finally, you can shift the timing of the other species relative to the first. In our example, the herbivore has access to younger plants and again are there fitness consequences?Yang and Rudolf call the full combination of possible fitness effects, across a number of timing mismatches, 'the ontogeny-phenology landscape'. By mapping fitness changes across this ontogeny-phenology landscape, researchers can offer better predictions, on top of just changes in range size or habitat use, about the possible affects of climate change. The obvious question, and Yang and Rudolf acknowledge this, is how to extend two-species ontogeny-phenology to multi-species communities. Of course, extending two-species interactions to communities is a question that plagues most of community ecology, but I think the solution is that researchers who know their systems often have intuition about the major players, and thus those species where phenology shifts should have disproportionate effects on other species. Such species could be the place to start. Another strategy would be a food web type approach, where species are lumped into broader trophic groups and we ask how shifts in certain trophic groups affect other groups.Regardless of how to extend this framework to multispecies assemblages, I see this paper as likely to be very influential. It gives researches a new focus and framework, where specific predictions about climate change can be made.Yang, L., & Rudolf, V. (2010). Phenology, ontogeny and the effects of climate change on the timing of species interactions Ecology Letters, 13 (1), 1-10 DOI: 10.1111/j.1461-0248.2009.01402.x... Read more »

Yang, L., & Rudolf, V. (2010) Phenology, ontogeny and the effects of climate change on the timing of species interactions. Ecology Letters, 13(1), 1-10. DOI: 10.1111/j.1461-0248.2009.01402.x

January 14, 2010
10:28 PM
72 views

Plant genotypic diversity supports pollinator diversity

by Marc Cadotte in The EEB and flow

Research over the past 20 years has shown that plant communities with greater diversity maintain higher productivity, greater stability and support more diverse arthropod assemblages. More recently, several experiments have shown that interspecific diversity (namely genotypic differences) also affects community functioning. Pollination is often considered an essential function, and does plant genotypic diversity affect pollinator diversity and frequency?In a recent paper in PLoS ONE, Genung and colleagues test whether plant genotypic diversity affects pollinator visits. They use an experimental system set-up by Greg Crutsinger that combines multiple genotypes of the goldenrod, Solidago altissima, and record pollinator visits over two years. Experimental plots contained 1, 3, 6, or 12 genotypes of S. altissima. After accounting for differences in abundance, Genung et al. show that as genotypic diversity increases, both pollinator richness and number of visits to the plot significantly increase. This increase is greater than expectations of randomly simulated assemblages combining proportional pollinator visits from monocultures.The previous research at the species-level has made a persuasive rationale to protect species diversity in order to maintain ecosystem functioning. Now, research like this is making a case that there are consequences for not explicitly considering genetic diversity in conservation planning and habitat restoration.Genung, M., Lessard, J., Brown, C., Bunn, W., Cregger, M., Reynolds, W., Felker-Quinn, E., Stevenson, M., Hartley, A., Crutsinger, G., Schweitzer, J., & Bailey, J. (2010). Non-Additive Effects of Genotypic Diversity Increase Floral Abundance and Abundance of Floral Visitors PLoS ONE, 5 (1) DOI: 10.1371/journal.pone.0008711... Read more »

Genung, M., Lessard, J., Brown, C., Bunn, W., Cregger, M., Reynolds, W., Felker-Quinn, E., Stevenson, M., Hartley, A., Crutsinger, G.... (2010) Non-Additive Effects of Genotypic Diversity Increase Floral Abundance and Abundance of Floral Visitors. PLoS ONE, 5(1). DOI: 10.1371/journal.pone.0008711

January 5, 2010
12:50 PM
99 views

Predicting invader success requires integrating ecological and land use patterns.

by Marc Cadotte in The EEB and flow

Disclaimer, this was modified from an editorial I wrote for the Journal of Applied Ecology.In the quest to understand species invasions, we often try to link the abundance and distribution of invaders to underlying ecological processes. For example, oft-studied are the links between exotic diversity and native richness or environmental heterogeneity. Seemingly independently, research into how specific land use or management activities affect invasion dynamics is also fairly common. While both research strategies are of fundamental importance, not often recognized, or at least explicitly studied, is that both ecological patterns and management activities simultaneously affect invasion success. Thus a truly integrative approach to understanding invader success must take into account variation in ecological communities and abiotic resource avalibility as well as land use patterns at multiple spatial scales. Such an approach is necessary if ecologists wish to predict potential invader abundance, spread and impact.Diez et al. Examine how environmental and management heterogeneity interact to influence patterns of Hieracium pilosella (Asteraceae) inasions in the South Island of New Zealand. The spread of H. Pilosella in New Zealand is threatening native habitats (tussock fields) and the livestock grazing industry. Diez et al. Asked how environmental and management regimes affect H. Pilosella abundance and distribution across six large farms on the South Island. This is an interesting and important question, not just because they are examining how human-caused and ecological variation interact to affect H. Pilosella dynamics, but also because these sources are heterogeneity are realized at different spatial scales.Diez et al. show that the abundance and distribution of H. Pilosella was significantly affected by the interaction of habitat type (i.e., short vs. tall tussocks) and farm management strategies (i.e., fertilization and grazing rates). At larger scales, H. Pilosella was more abundant in tall tussock habitats and was unaffected by fertilization, while in short tussocks, it was less abundant in fertilized patches. At small scales, H. Pilosella was less likely to be found in short tussocks with high exotic grass cover and high productivity (measured as site soil moisture and solar radiation). Conversely, in tall tussocks, H. Pilosella was more likely to be found on sites with high natural productivity. Diez et al. were able to tease these complex causal mechanism apart by using Bayesian multilevel linear models, for which they included example R code in an online appendix.While it is a truism in ecology to say that heterogeneity affects ecological patterns, this paper deserves mention because they convincingly show that the spread of noxious exotic plants in a complex landscape, can potentially predicted by understanding the invader success in different habitat types and land management strategies. In their case they show how human activities, which were not designed to affect H. Pilosella, can strongly affect abundance in different habitat types. This type of approach to understanding invader dynamics can potentially arm managers with the ability to use existing land use strategies to predict how and where further invader targeting would be most useful.Diez, J., Buckley, H., Case, B., Harsch, M., Sciligo, A., Wangen, S., & Duncan, R. (2009). Interacting effects of management and environmental variability at multiple scales on invasive species distributions Journal of Applied Ecology DOI: 10.1111/j.1365-2664.2009.01725.x... Read more »

Diez, J., Buckley, H., Case, B., Harsch, M., Sciligo, A., Wangen, S., & Duncan, R. (2009) Interacting effects of management and environmental variability at multiple scales on invasive species distributions. Journal of Applied Ecology. DOI: 10.1111/j.1365-2664.2009.01725.x

December 16, 2009
09:51 PM
151 views

Parastie competition enhances host survival

by Marc Cadotte in The EEB and flow

Contracting a parasite is bad. But is getting colonized by multiple parasitic species worse? This is an interesting and important question. The host is a resource, which can support a limited number of parasitic individuals, and so how does competition affect parasitic species and host mortality?This was the premise of a recent paper by Oliver Balmer and colleagues, studying trypanosome infection of mice hosts. They engineered two transgeneic strains of the protozoan parasite, Trypanosoma brucei (African sleeping sickness), to fluoresce different colors in order to assess infections. They infected mice with each strain separately and together and measured host survival and parasite density.They found that when both strains were present, they competitively suppressed each other and that the level of suppression depended on the initial density of each strain. One of the strains was more virulent than the other, and infection by both strains reduced mortality by 15% compared to infection by the virulent strain only. This is due to the suppression of the virulent strain by the low virulent strain.The authors argue that strain source and intraspecific genetic diversity can have an important effect on host mortality. I would also argue that understanding interspecific interactions and within-host niche differences, would also be critical.What a cool use of molecular technology to test basic hypotheses about disease ecology.Balmer, O., Stearns, S., Schötzau, A., & Brun, R. (2009). Intraspecific competition between co-infecting parasite strains enhances host survival in African trypanosomes Ecology, 90 (12), 3367-3378 DOI: 10.1890/08-2291.1... Read more »

Balmer, O., Stearns, S., Schötzau, A., & Brun, R. (2009) Intraspecific competition between co-infecting parasite strains enhances host survival in African trypanosomes. Ecology, 90(12), 3367-3378. DOI: 10.1890/08-2291.1

November 25, 2009
10:13 PM
203 views

Taking below-ground processes seriously: plant coexistence and soil depth

by Marc Cadotte in The EEB and flow

Some of the earliest ecologists, like Eugen Warming and Christen Raunkiaer, were enthralled with the minutia of the differences in plant life forms and how these differences determined where plants lived. They realized that differences in plant growth forms corresponded to how different plants made their way in the world. Since this early era, understanding the mechanisms of plant competition is one of the most widely-studied aspects of ecology. This is such an important aspect of ecology because understanding plant coexistence allows us to understand what controls productivity in the basal trophic level for most terrestrial food webs. There are a plethora of plausible mechanisms for how plants are able to coexist, and most involve above-ground partitioning strategies (such as different leaf shapes) or phenological differences (such as germination or bolting timing). Yet, below-ground interactions among plants as a way to understand competition and coexistence have been making a strong resurgence in the literature lately. This resurgence has been driven by new hypotheses and technologies.In what is probably the best hypothesis test of the role for below-ground niche partitioning, Mathew Dornbush and Brian Wilsey reveal how soil depth can affect coexistence. They seeded 36 tallgrass prairie species into plot that were either shallow, medium or deep soiled, and asked if species richness and diversity were affected after 3 years. They found that species richness significantly increased with increased soil depth, revealing that deeper soils likely had greater niche opportunities for species. Not only did deeper soils harbor greater richness, but compositions were non-random subsets. The species inhabiting shallow soils were a subset of medium soils, and medium a subset of deep. This means that increasing depth opened new niche opportunities, unique from the ones for shallow soils.This study is the first field-based experiment of soil depth and coexistence, that I know of and the results are compelling. Plant species are segregating below-ground niches, and perhaps we look for other partitioning strategies for species that inhabit the same soil depth.Dornbush, M., & Wilsey, B. (2009). Experimental manipulation of soil depth alters species richness and co-occurrence in restored tallgrass prairie Journal of Ecology DOI: 10.1111/j.1365-2745.2009.01605.xOther notable recent papers on below-ground processes:Bartelheimer, M., Gowing, D., & Silvertown, J. (2009). Explaining hydrological niches: the decisive role of below-ground competition in two closely related species Journal of Ecology DOI: 10.1111/j.1365-2745.2009.01598.xCramer, M., van Cauter, A., & Bond, W. (2009). Growth of N-fixing African savanna species is constrained by below-ground competition with grass Journal of Ecology DOI: 10.1111/j.1365-2745.2009.01594.xMeier, C., Keyserling, K., & Bowman, W. (2009). Fine root inputs to soil reduce growth of a neighbouring plant via distinct mechanisms dependent on root carbon chemistry Journal of Ecology, 97 (5), 941-949 DOI: 10.1111/j.1365-2745.2009.01537.x... Read more »

Dornbush, M., & Wilsey, B. (2009) Experimental manipulation of soil depth alters species richness and co-occurrence in restored tallgrass prairie. Journal of Ecology. DOI: 10.1111/j.1365-2745.2009.01605.x

Bartelheimer, M., Gowing, D., & Silvertown, J. (2009) Explaining hydrological niches: the decisive role of below-ground competition in two closely related species . Journal of Ecology. DOI: 10.1111/j.1365-2745.2009.01598.x

Cramer, M., van Cauter, A., & Bond, W. (2009) Growth of N -fixing African savanna species is constrained by below-ground competition with grass . Journal of Ecology. DOI: 10.1111/j.1365-2745.2009.01594.x

Meier, C., Keyserling, K., & Bowman, W. (2009) Fine root inputs to soil reduce growth of a neighbouring plant via distinct mechanisms dependent on root carbon chemistry. Journal of Ecology, 97(5), 941-949. DOI: 10.1111/j.1365-2745.2009.01537.x

November 9, 2009
10:14 AM
199 views

Emergent linkages in seemingly unconnected food chains

by Marc Cadotte in The EEB and flow

Food webs are notoriously complex, and a difficult aspect of ecology is to offer a priori model-derived predictions of food web processes. There are some ecologists, such Neo Martinez and Jordi Bascompte, who have advanced our understanding of the general mechanisms of food web properties and dynamics through tools such as network theory. Such advanced approaches rely on direct interactions among species, or at least indirect interactions that are mediated through changes in abundance of different network players. However, what is missing from our general understanding of food web interactions is the role that behavioral responses can affect patterns of consumption and network connectivity.Washington State University ecologists, Renée Prasad and William Snyder convincingly show how behavioral responses to predation can fundamentally alter food web interactions and link previously independent predator-prey interactions. They used two spatially independent insect predator-prey links in a novel, factorially-designed experiment. The two food chains consisted of a ground-based one, where ground beetles consume fly eggs and a plant-based one, where green peach aphids feed on the plants and are consumed by lady beetles. Under the ground-based chain only, the ground-based chain plus aphids, or ground-based chain plus lady beetles, the ground beetles consume a high proportion of the fly eggs. However, when both aphids and lady beetles are present, aphids respond to lady beetles by dropping off the plants and the ground beetles switch from consuming fly eggs to aphids. Under this last treatment, very few fly eggs are consumed, fundamentally altering the strength of the linkages in the two food chains and connecting them together.This research highlights the inherent complexity in trying to understand multispecies systems, where the actors potentially have behavioral responses to other species, changing the nature of interactions. These types of responses may also generally increase the connectedness of such networks, which may result in more stable food webs, but this would need to be empirically tested. Regardless, this type of experiment offers food-for-thought to scientists trying to work general processes into a broad understanding of food web dynamics.Prasad, R., & Snyder, W. (2009). A non-trophic interaction chain links predators in different spatial niches Oecologia DOI: 10.1007/s00442-009-1486-7... Read more »

Prasad, R., & Snyder, W. (2009) A non-trophic interaction chain links predators in different spatial niches. Oecologia. DOI: 10.1007/s00442-009-1486-7

October 21, 2009
05:04 PM
258 views

Adaptation and dispersal = (mal)adapted

by Marc Cadotte in The EEB and flow

Ever since Darwin, we often think of organisms as being in a constant battle against other organisms and local environments. Thus natural selection and the resulting arms race results in organisms highly adapted to local conditions and against local antagonists. At the same time, and especially driven by theoretical advances in the 1990's, researchers began to ask how dispersal -that is, the flow of genetic material from elsewhere, can disrupt local adaptation. On the one hand it may provide genetic variation allowing for novel solutions to new difficulties. On the other hand, dispersal may reduce the prevalence of fitness-increasing genes within local populations.In a simple but elegant experiment, Jill Anderson and Monica Geber performed a reciprocal transplant experiment, moving Elliott's Blueberry plants between two habitats. One population was from highland, dryer habitats and the other from moist lowlands. They further evaluated performance in greenhouse conditions. Their results, published in Evolution, show that these two populations have not specialized to local conditions. Rather, due to asymmetric gene transfer, lowland individuals actually performed better when planted in highlands than compared to their home habitat. Further, in the greenhouse trials, lowland species did not perform better under higher moisture conditions. While genetic or physiological constraints may also limit adaptation, Anderson and Geber present a fairly convincing case that gene flow is the culprit.These results reveal that populations may actually be relatively mal-adapted to local conditions, which has numerous consequences. For example, we need to be cognizant of adaptations to particular conditions when selecting populations for use in habitat restoration and when trying to predict response to altered climatic or land-use conditions. Importantly what does this mean for multi-species coexistence? Dispersal seems to limit the ability to adapt, and thus, better use local resources or maximize fitness, making for a better competitor. At the same time, dispersal can offset high death rates, allowing for the persistence of a population that would otherwise go extinct. Understanding how these two consequences of dispersal shape populations and communities is an interesting question, and work like Anderson and Geber's provides a foundation for future studies.Anderson, J., & Geber, M. (2009). DEMOGRAPHIC SOURCE-SINK DYNAMICS RESTRICT LOCAL ADAPTATION IN ELLIOTT'S BLUEBERRY ( ) Evolution DOI: 10.1111/j.1558-5646.2009.00825.x... Read more »

Anderson, J., & Geber, M. (2009) DEMOGRAPHIC SOURCE-SINK DYNAMICS RESTRICT LOCAL ADAPTATION IN ELLIOTT'S BLUEBERRY ( ) . Evolution. DOI: 10.1111/j.1558-5646.2009.00825.x

October 7, 2009
11:38 AM
263 views

Exotic plants integrate into plant-pollinator networks

by Marc Cadotte in The EEB and flow

At almost any spot on the globe, there are species present that are not native to that locale, having been transported by human activities. Whether and how exotic species impact communities is a multifaceted problem that requires understanding the multitude of direct and indirect species interactions that occur. In a paper published in the Proceedings of the Royal Society, B, Montserrat Vila and colleagues asked if exotic plants where integrated into plant-pollinator networks, and whether this integration had any observable impacts on these networks. This is an important question, as most ecological theory predicts that plant-pollinator networks are actually quite resilient to perturbations since most associations tend to be between generalists as opposed to the more susceptible specialists.They studied invaded plant communities across Europe, observing pollinator visits to flowers in multiple 50 x 50 m plots. They calculated connectance as the number of interactions standardized by network size. They showed that exotics fully integrated into plant-pollinator networks. Exotic species accounted for 42% of all pollinator visits and 24% of all network connections -a testament to the overall abundance of exotics in many communities. However, these exotics did not affect overall changes in network connectedness, revealing that these networks are quite robust to invasions.That said, researchers must now ask if this is true in networks that do contain high numbers of specialists (e.g., orchids) or if the relative few specialists in generalist-dominated systems are more susceptible to changes from exotics.Vila, M., Bartomeus, I., Dietzsch, A., Petanidou, T., Steffan-Dewenter, I., Stout, J., & Tscheulin, T. (2009). Invasive plant integration into native plant-pollinator networks across Europe Proceedings of the Royal Society B: Biological Sciences, 276 (1674), 3887-3893 DOI: 10.1098/rspb.2009.1076... Read more »

Vila, M., Bartomeus, I., Dietzsch, A., Petanidou, T., Steffan-Dewenter, I., Stout, J., & Tscheulin, T. (2009) Invasive plant integration into native plant-pollinator networks across Europe. Proceedings of the Royal Society B: Biological Sciences, 276(1674), 3887-3893. DOI: 10.1098/rspb.2009.1076

September 25, 2009
10:09 PM
342 views

Global warming and shifts in food web strucutre

by Marc Cadotte in The EEB and flow

Predicting the effects of global warming on biological systems is of critical importance for informing proactive policy decisions. Most research so far has been on trying to predict shifts in species distributions and changes in interactions within local habitats. But what many of these studies assume is that the basic biological processes and requirements of the individual species will not change -that is their biology is fixed and they simply need to find the place that best suits them. Not so, say Mary O'Connor and colleagues, in a just-released study in PLoS Biology.O'Connor and colleagues experimentally warmed marine microcosms and tested two alternative hypotheses on food web structure: 1) that productivity increases with warming; and 2) warming increases metabolic rates, thus changing consumer-autotroph (i.e., primary producers) interactions. What they found was that warming indeed altered consumer-autotroph interactions. Warming increased base metabolic rates of consumers, as well as primary production, and the net effect was that food webs shifted towards increasing consumer control (i.e., top-down control).What this research means is that global warming may alter food web interactions by increasing resource needs of organisms as their metabolic rates increase. This may increase the stress on communities and change diversity patterns as increased needs may shift competitive hierarchies or affect autotroph's ability to withstand consumer effects.O'Connor, M., Piehler, M., Leech, D., Anton, A., & Bruno, J. (2009). Warming and Resource Availability Shift Food Web Structure and Metabolism PLoS Biology, 7 (8) DOI: 10.1371/journal.pbio.1000178... Read more »

O'Connor, M., Piehler, M., Leech, D., Anton, A., & Bruno, J. (2009) Warming and Resource Availability Shift Food Web Structure and Metabolism. PLoS Biology, 7(8). DOI: 10.1371/journal.pbio.1000178

September 21, 2009
09:06 PM
319 views

Everything but extinct: invasion impacts on native diversity

by Marc Cadotte in The EEB and flow

There has been a persistent debate in the plant invasions literature about whether exotic plant invasions are a major threat to native plant persistence. While there are clear examples of animal invasions resulting in large scale extinction -e.g., the brown tree snake or Nile perch, evidence has been ambiguous for plants. Most ecologists are not so sanguine as to actually conclude that plant invasions are not a threat, and I think most believe that plant invader effects are an issue of temporal and spatial scale and that the worst is yet to come.In a forthcoming paper from Heinke Jäger and colleagues in the Journal of Ecology, Cinchona pubescens invasions on the Galápagos Islands were monitored in long-term plots for more than seven years. What they found was that there was a four-fold increase in Cinchona density as the invasion progressed and that this increase had measurable effects on native species abundance. While they did not observe any native extirpations in their plots, native densities decreased by at least 50%. Of the greatest concern was that Island endemics appear to the most susceptible to this invasion.What these results show is that, while there were not any observed extinctions, there were serious deleterious changes to native diversity. Further, the native species, and especially the endemics, are now more susceptible to other invasions or disturbances due to their lower abundances. The impact of exotic invaders may not be readily apparent but may be a major contributor to increased extinction risk.Jäger, H., Kowarik, I., & Tye, A. (2009). Destruction without extinction: long-term impacts of an invasive tree species on Galápagos highland vegetation Journal of Ecology DOI: 10.1111/j.1365-2745.2009.01578.x... Read more »

Jäger, H., Kowarik, I., & Tye, A. (2009) Destruction without extinction: long-term impacts of an invasive tree species on Galápagos highland vegetation. Journal of Ecology. DOI: 10.1111/j.1365-2745.2009.01578.x

August 25, 2009
06:40 AM
329 views

March of polyploids!

by Marc Cadotte in The EEB and flow

Speciation by polyploidy (see here for a general description of polyploidy) is one of the mechanisms of speciation and evolutionary diversification. We all learn about it in Bio 101, right after allopatry and sympatry. It is thought to be an especially important driver of speciation in plants, and anecdotal evidence, such as the origination of the invasive polyploid, Spartina anglica in the UK in the 1800's, reinforced that view. But how important has been unanswered until now.In a new publication in PNAS by Wood et al. -from the Loren Rieseberg lab (one of the best lab homepages BTW) this questions has been answered. The authors go through all available chromosome counts on the Missouri Botanical Garden's Index to Plant Chromosome Numbers, and assess the proportion of polyploid species. They find that about 15% of all angiosperm speciation events coincided with an increase in chromosome number (and about 30% of fern species). Further, about 35% of all genera contain polyploids. Looking across the phylogeny of major plant groups, they find that all major lineages, except Gymnosperms, have significant proportions of polyploids (again with ferns have the greatest proportion). Polyploidy is a ubiquitous feature of plant diversity and a major driver of plant speciation. And now we can quantify just how important.Wood, T., Takebayashi, N., Barker, M., Mayrose, I., Greenspoon, P., & Rieseberg, L. (2009). The frequency of polyploid speciation in vascular plants Proceedings of the National Academy of Sciences, 106 (33), 13875-13879 DOI: 10.1073/pnas.0811575106... Read more »

Wood, T., Takebayashi, N., Barker, M., Mayrose, I., Greenspoon, P., & Rieseberg, L. (2009) The frequency of polyploid speciation in vascular plants. Proceedings of the National Academy of Sciences, 106(33), 13875-13879. DOI: 10.1073/pnas.0811575106

August 18, 2009
10:06 AM
306 views

Unifying invader success and impact

by Marc Cadotte in The EEB and flow

Something that has continuously bothered me about our collective narrative concerning invasions has been the conflicting processes determining invader success and impact. Numerous studies (including some of my own) show that invaders are successful often because they are different from residents. That is, they are thought to occupy some unique niche. However, occupying a unique niche means that competition is minimized and these successful invaders should have relatively low impact on residents. Conversely, species that have large impacts are thought to be superior competitors, but why are they able to be so successful?In a new paper in the Journal of Ecology, Andrew MacDougall, Benjamin Gilbert and Jonathan Levin use Peter Chesson's framework where ability for two species to coexistence (or conversely the strength of competitive exclusion) is a process relative to two factors -the magnitude of fitness differences and the degree of resource use overlap. Here competitive exclusion is rapid if species have a large fitness difference and high resource overlap, and slow if fitness differences are low. Species that are successful because of reduced resource overlap likely have little impact unless there are large fitness inequalities.If we then view the invasions process on a continuum (see figure), then by determining basic fitness and resource use, we can predict success and impact. This is an exciting development and I hope it inspires a new generation of experiments.MacDougall, A., Gilbert, B., & Levine, J. (2009). Plant invasions and the niche Journal of Ecology, 97 (4), 609-615 DOI: 10.1111/j.1365-2745.2009.01514.x... Read more »

MacDougall, A., Gilbert, B., & Levine, J. (2009) Plant invasions and the niche. Journal of Ecology, 97(4), 609-615. DOI: 10.1111/j.1365-2745.2009.01514.x

May 28, 2009
06:27 PM
589 views

How long does it take for an ecosystem to recover?

by Marc Cadotte in The EEB and flow

Numerous human activities, such as logging, fishing, pollution and the introduction of exotic species negatively impact ecosystems around the world. These negative impacts mean ecosystems lose species diversity, biomass production, carbon storage, and nutrient uptake. An important question is, how long does it take for ecosystems to recover from perturbations. The answer to this question can inform conservation policy and strategies and could help focus management resources.In a recent PLoS ONE paper, Jones and Schmitz attempt to answer this question by reviewing 240 published studies that examine post-disturbance ecosystem diversity and function. While they report that many ecosystems recover on the order of decades and that this is likely more rapid than previously thought, there are some important caveats. First, is that only about half of the 240 studies report a recovered state and either they were not carried out long enough or there are certain types of disturbances or systems where recovery takes much longer. Second is that there are important differences among habitat types. For example benthic algal recovery to hurricanes or oil spills may take 2-10 years, while the recovery of tree diversity to logging may take 20 to 100 years (or more). Thirdly, different measures of ecosystems general resulted in differing recovery times. For example, bird populations may recover quite quickly to logging (likely because they are migratory), whereas soil microbial communities and processes may take many decades due to changes in the soil environment. Finally, the nature of the disturbance can be an important determinant of time to recovery. Logging and agriculture require the greatest recovery time, while large storms and oil spills appear to require relative little time.While these results may give us a general picture of ecosystem recovery, the data they use highlight the importance of knowing how disturbance type affect recovery and how different ecosystem measures can alter recovery time estimates. Jones, H., & Schmitz, O. (2009). Rapid Recovery of Damaged Ecosystems PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005653... Read more »

Jones, H., & Schmitz, O. (2009) Rapid Recovery of Damaged Ecosystems. PLoS ONE, 4(5). DOI: 10.1371/journal.pone.0005653

May 20, 2009
07:19 PM
529 views

Fire and the changing world

by Marc Cadotte in The EEB and flow

This is probably the most appropriate blog I have ever written. My family and I were evacuated two weeks ago because of the Jesusita fire in Santa Barbara, and several homes in our neighborhood were lost. Here in Santa Barbara we have experienced multiple years of extremely large fires, with this last one occurring much earlier than previous fires.Wildfires have been a part of the Earth’s biota likely since organisms first died and dried on land. Ecosystems have been shaped by fire, numerous organisms have evolved strategies to cope with fire and human cultural development has close tied to fire. In a recent review paper in Science by David Bowman, Jennifer Balch and colleagues, they asked the question: how have fires changed and what does the future look like? Human activities are changing fire patterns and climate change may be entering a feedback with fire. Global warming has been linked to increases in extreme fire weather, making large, destructive fires more probable. However, these large fires feedback into this loop because they release compounds that have strong greenhouse effects. Further, smoke plumes inhibit cloud formation, reinforcing the dry conditions that lead to the fires in the first place.They argue that fire needs to be incorporating into models of climate change and especially those that link ecosystem properties climate change. Fire may change the distribution of specific habitat types beyond that predicting by responses to climate change alone.Bowman, D., Balch, J., Artaxo, P., Bond, W., Carlson, J., Cochrane, M., D'Antonio, C., DeFries, R., Doyle, J., Harrison, S., Johnston, F., Keeley, J., Krawchuk, M., Kull, C., Marston, J., Moritz, M., Prentice, I., Roos, C., Scott, A., Swetnam, T., van der Werf, G., & Pyne, S. (2009). Fire in the Earth System Science, 324 (5926), 481-484 DOI: 10.1126/science.1163886... Read more »

Bowman, D., Balch, J., Artaxo, P., Bond, W., Carlson, J., Cochrane, M., D'Antonio, C., DeFries, R., Doyle, J., Harrison, S.... (2009) Fire in the Earth System. Science, 324(5926), 481-484. DOI: 10.1126/science.1163886

May 1, 2009
01:48 AM
484 views

Enrichment and diversity loss: a mechanism tested

by Marc Cadotte in The EEB and flow

To paraphrase Thomas Henry Huxley: How stupid of us not to have thought of that!In what has to be one of the most elegant and simple experiments I've seen in a long time, Yann Hautier, Pascal Niklaus and Andy Hector tested a basic mechanism of why nutrient enrichment results in species loss. This is a critically important issue as it has been repeatedly shown that while adding nitrogen to plant communities causes increases in productivity, species go locally extinct. We may bare witness to local diversity declines because human activity has greatly increased nutrient deposition. This pattern has been observed for a couple of decades, but the exact mechanism has never been adequately tested, with some camps believing that enrichment increases below-ground competition for other resources that become limiting, or above ground for light.As reveled in the most recent issue of Science, Hautier et al. performed an exceedingly simple experiment; they added light to the understory of plant communities with or without nitrogen additions. They made two compelling observations. First, when communities were enriched without elevated light, they lost about 3 of the 6 initial species compared to the control, while light addition in the enriched communities maintained the 6 member community (as did a light only treatment). The second result was that the light plus nitrogen treatment obtained much higher biomass than either the nitrogen or light only treatments, and in fact the light only treatment did not significantly increase productivity, meaning that the communities are not normally light-limited. Further, they failed to detect any elevated belowground competition for other resources.These results reveal that nutrient enrichment causes diversity loss because increased plant size increases light competition and plants that grow taller with elevated nitrogen are better light competitors. An old problem solved with the right experiment.Hautier, Y., Niklaus, P., & Hector, A. (2009). Competition for Light Causes Plant Biodiversity Loss After Eutrophication Science, 324 (5927), 636-638 DOI: 10.1126/science.1169640... Read more »

Hautier, Y., Niklaus, P., & Hector, A. (2009) Competition for Light Causes Plant Biodiversity Loss After Eutrophication. Science, 324(5927), 636-638. DOI: 10.1126/science.1169640

April 22, 2009
06:10 PM
543 views

People value rare species; at least from their computers

by Marc Cadotte in The EEB and flow

Do people value rare species more than common ones? This is an important question for conservation because not only does valuation justify public funds being spent conserving rare species, but valuation can have negative implications as well. In what is called the ‘anthropogenic Allee effect’, increased valuation can increase species desirability –thus enhancing monetary value for exotic pets, building ecotourism lodges in sensitive habitats, or exotic tasty dishes (ah, the freshman). In what is probably the most unique approach to assessing whether behavior is affected by the notion of species rarity, Angula and Courchamp, at the Université Paris Sud, used a web-based slideshow measure the amount of time people would wait to see a slideshow of rare versus common species.Cleverly, they created a French website where visitors could select to view either a slideshow of common or rare species (and the links randomly changed positions on the site). The trick was that a download status bar appears and freezes near the end, and so Angula and Courchamp were able to measure how many visitors selected the rare species show and how long they waited until they gave up. Visitors were much more likely to select the rare species and to wait longer to see them.I think that this study is extremely neat for two reasons. First it offers a novel way to quantify valuation, and second, it shows how the internet can be used to assess conservation issues in an efficient low-cost way.Now will they please just show us the pictures of the cute, endangered species!Angulo, E., & Courchamp, F. (2009). Rare Species Are Valued Big Time PLoS ONE, 4 (4) DOI: 10.1371/journal.pone.0005215... Read more »

Angulo, E., & Courchamp, F. (2009) Rare Species Are Valued Big Time. PLoS ONE, 4(4). DOI: 10.1371/journal.pone.0005215

March 27, 2009
01:47 PM
641 views

The evolutionary meaning of autumn colors

by Marc Cadotte in The EEB and flow

As a kid growing up in Ontario, Canada, I have vivid memories of vast expanses of forests set ablaze by their autumn colors. Whole landscapes look like the canvas of a painter whose love of red, orange, gold and yellow are readily apparent. But, like most biologists, I had been taught that these colors are simply the by-product of leaf senescence, nothing more than a biochemical accident. I was amazed to read Marco Archetti's recent work showing that there may actually be adaptive benefits to changing leaf color in autumn and for particular colors. Generally the adaptive benefits involve either protection against abiotic factors or as a response to plant-animal interactions. One of his interesting results is that autumn coloration has evolved repeatedly and cannot be explained by being related to an ancestor who changed colors, rather that there must be some other evolutionary or adaptive explanation. While he suggests a large number of candidate hypotheses, some more plausible than others, I'll list five for example:1) Sunscreen: Pigments provide photoprotection against photooxidation during the recovery of nutrients.2) Leaf warming: Colors absorb light and warm the leaves during cooling temperatures.3) Coevolution: Tells overwintering insects that the tree is not suitable (poisonous or low nutrition) for hibernation.4) Camouflage: Many insects lack red photoreceptor, making leaves difficult to see -thus protecting trees from overwintering pests.5) Unpalatability: Pigments (e.g., red -anthocyanins) are unpalatable.So, we may quibble about particular hypotheses, but the point for me is that there may be deeper explanations as to why certain species produce the vivid colors they do. At a minimum, Archetti provides amunition to experimental botnists and evolutionary biologists for testing new hypotheses. I'll never look at an autumn forest the same again.Archetti, M. (2009). Classification of hypotheses on the evolution of autumn colours Oikos, 118 (3), 328-333 DOI: 10.1111/j.1600-0706.2008.17164.xArchetti, M. (2008). Phylogenetic analysis reveals a scattered distribution of autumn colours Annals of Botany, 103 (5), 703-713 DOI: 10.1093/aob/mcn259Archetti, M., Döring, T., Hagen, S., Hughes, N., Leather, S., Lee, D., Lev-Yadun, S., Manetas, Y., Ougham, H., & Schaberg, P. (2009). Unravelling the evolution of autumn colours: an interdisciplinary approach Trends in Ecology & Evolution, 24 (3), 166-173 DOI: 10.1016/j.tree.2008.10.006... Read more »

Archetti, M. (2009) Classification of hypotheses on the evolution of autumn colours. Oikos, 118(3), 328-333. DOI: 10.1111/j.1600-0706.2008.17164.x

Archetti, M. (2008) Phylogenetic analysis reveals a scattered distribution of autumn colours. Annals of Botany, 103(5), 703-713. DOI: 10.1093/aob/mcn259

Archetti, M., Döring, T., Hagen, S., Hughes, N., Leather, S., Lee, D., Lev-Yadun, S., Manetas, Y., Ougham, H., & Schaberg, P. (2009) Unravelling the evolution of autumn colours: an interdisciplinary approach. Trends in Ecology , 24(3), 166-173. DOI: 10.1016/j.tree.2008.10.006

March 23, 2009
02:37 PM
689 views

Conserve now or wait for the data?

by Marc Cadotte in The EEB and flow

E. O. Wilson, referring to the ethical imperative we should apply to the conservation of life, said “The ethical imperative should be, first of all, prudence. We should judge every scrap of biodiversity as priceless while we learn to use it and to come to understand what it means to humanity” (pg. 351, The Diversity of Life). Although, I would argue we should aim to learn biodiversity’s value, both intrinsic and extrinsic, as opposed to what it solely means to humanity, his point is protect now, study later. The reason being that there is still so much to learn in order to adequately assess the Earth’s biological riches, by the time we inventory and map a fraction of biodiversity, we would have lost numerous unique regions and species. Of course the opposing point of view is that we need detailed information in order to best use limited resources to best protect biodiversity. This is a major philosophical divide. In a recent, important paper by Hedley Grantham and colleagues published in Ecology Letters, the question of how long should we wait to take conservation actions was empirically tested.The authors used simulations based on 20 years of habitat loss data from the biologically-rich Fynbos region of South Africa and knowledge about spatial distribution of Protea diversity. Protea surveys (The Protea Atlas) have been carried out over 20 years, inventorying 40,000 plots and recording 381 species within the Proteaceae. They began their simulations with no information about Protea diversity patterns and included annually increasing knowledge, set against annual habitat destruction. They showed that waiting to make conservation decisions after only 2 years resulted in species loss, because habitat loss far outweighed any advantage to gaining more information. Further, more detailed information did not appear to increase the effectiveness of conservation decisions over cruder habitat-level maps.The philosophical divide between protect now-learn later versus the need for detailed information to maximize resources appears bridgeable. It seems that by just accumulating some rough data may go a long way towards making those important conservation decisions. Of course, the irony is that this study needed 20 years of data to adequately assess this.Grantham, H., Wilson, K., Moilanen, A., Rebelo, T., & Possingham, H. (2009). Delaying conservation actions for improved knowledge: how long should we wait? Ecology Letters, 12 (4), 293-301 DOI: 10.1111/j.1461-0248.2009.01287.x... Read more »

Grantham, H., Wilson, K., Moilanen, A., Rebelo, T., & Possingham, H. (2009) Delaying conservation actions for improved knowledge: how long should we wait?. Ecology Letters, 12(4), 293-301. DOI: 10.1111/j.1461-0248.2009.01287.x

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