Oikos

Caplat, P.; Cheptou, P.‐O.; Diez, J.; Guisan, A.; Larson, B. M. H.; Macdougall, A. S.; Peltzer, D. A.; Richardson, D. M.; Shea, K.; van Kleunen, M.; Zhang, R.; Buckley, Y. M.

doi: 10.1111/j.1600-0706.2013.00430.xpmid: N/A

Synthesis Prediction and management of species responses to climate change is an urgent but relatively young research field. Therefore, climate change ecology must by necessity borrow from other fields. Invasion ecology is particularly well‐suited to informing climate change ecology because both invasion ecology and climate change ecology address the trajectories of rapidly changing novel systems. Here we outline the broad range of active research questions in climate change ecology where research from invasion ecology can stimulate advances. We present ideas for how concepts, case‐studies and methodology from invasion ecology can be adapted to improve prediction and management of species responses to climate change. A major challenge in this era of rapid climate change is to predict changes in species distributions and their impacts on ecosystems, and, if necessary, to recommend management strategies for maintenance of biodiversity or ecosystem services. Biological invasions, studied in most biomes of the world, can provide useful analogs for some of the ecological consequences of species distribution shifts in response to climate change. Invasions illustrate the adaptive and interactive responses that can occur when species are confronted with new environmental conditions. Invasion ecology complements climate change research and provides insights into the following questions: 1) how will species distributions respond to climate change? 2) how will species movement affect recipient ecosystems? And 3) should we, and if so how can we, manage species and ecosystems in the face of climate change? Invasion ecology demonstrates that a trait‐based approach can help to predict spread speeds and impacts on ecosystems, and has the potential to predict climate change impacts on species ranges and recipient ecosystems. However, there is a need to analyse traits in the context of life‐history and demography, the stage in the colonisation process (e.g. spread, establishment or impact), the distribution of suitable habitats in the landscape, and the novel abiotic and biotic conditions under which those traits are expressed. As is the case with climate change, invasion ecology is embedded within complex societal goals. Both disciplines converge on similar questions of ‘when to intervene?‘ and ‘what to do?‘ which call for a better understanding of the ecological processes and social values associated with changing ecosystems.

Polley, H. Wayne; Isbell, Forest I.; Wilsey, Brian J.

doi: 10.1111/j.1600-0706.2013.00338.xpmid: N/A

Synthesis The temporal stability of plant production is greater in communities with high than low species richness, but stability also may depend on species abundances and growth‐related traits. Annual precipitation varied by greater than a factor of three over 11 years in central Texas, USA leading to large variation in production. Stability was greatest in communities that were not dominated by few species and in which dominant species rooted shallowly, had dense leaves, or responded to the wettest year with a minimal increase in production. Stability may depend as much on species abundances and functional traits as on species richness alone. Aboveground net primary productivity (ANPP) varies in response to temporal fluctuations in weather. Temporal stability of community ANPP may be increased by increasing plant species richness, but stability often varies at a given richness level implying a dependence on abundances and functional properties of member species. We measured stability in ANPP during 11 years in field plots (Texas, USA) in which we varied the richness and relative abundances of perennial grassland species at planting. We sought to identify species abundance patterns and functional traits linked to the acquisition and processing of essential resources that could be used to improve richness‐based predictions of community stability. We postulated that community stability would correlate with abundance‐weighted indices of traits that influence plant responses to environmental variation. Annual precipitation varied by a factor of three leading to large inter‐annual variation in ANPP. Regression functions with planted and realized richness (species with > 1% of community ANPP during the final four years) explained 32% and 25% of the variance in stability, respectively. Regression models that included richness plus the fraction of community ANPP produced by the two most abundant species in combination with abundance‐weighted values of either the fraction of sampled root biomass at 20–45 cm depth, leaf dry matter content (LDMC), or response to greater‐than‐average precipitation of plants grown in monocultures explained 58–69% (planted richness) and 58–64% (realized richness) of the variance in stability. Stability was greatest in communities that were not strongly dominated by only two species and in which plants rooted shallowly, had high values of LDMC, or responded to the wettest year with a minimal increase in ANPP. Our results indicate that the temporal stability of grassland ANPP may depend as much on species abundances and functional traits linked to plant responses to precipitation variability as on species richness alone.

Gonsamo, Alemu; D’odorico, Petra; Pellikka, Petri

doi: 10.1111/j.1600-0706.2013.00369.xpmid: N/A

Canopy structural parameters are often used to give adequate representation of vegetated ecosystems for various purposes including primary productivity, climate system, water and carbon gas exchanges, and radiation extinction. Canopy structural parameters are usually described using several pseudo‐synonymous terms, often measuring different components of vegetation canopies. Standardization in the definitions has fallen short, leading to confusion of terms even in standard text books making the comparison of historic measures futile. Here we clarify concepts that have been used for fractional canopy element cover and openness measures. The fractional canopy element cover and openness concepts considered are canopy closure, canopy cover, canopy openness, crown closure, crown completeness, crown cover, crown porosity, site openness and tilt openness. New methodologies are presented to obtain large scale fractional canopy element cover and openness measures using hemispherical photography. The new methodologies and variations in definitions of fractional canopy element cover and openness concepts are demonstrated using photographic measurements in complex topography. The results indicate that both fractional canopy element cover and openness parameters can be estimated with a few point‐based measurements using hemispherical photography. Hemispherical photography is therefore less time, labour and resource intensive, as compared to point based measuring techniques of canopy element cover and openness. Most of the commonly and interchangeably used concepts of fractional canopy element cover and openness measures represent physically different structural properties of a vegetated ecosystem.

Choquenot, David; Forsyth, David M.

doi: 10.1111/j.1600-0706.2012.20976.xpmid: N/A

The exploitation ecosystems hypothesis (EEH) proposes that 1) plant biomass reflects the primary productivity of an ecosystem modified by the regulating effect of herbivory, and 2) herbivore abundance reflects the productivity of plants modified by the regulating effect of predation. Primary productivity thus determines the number of trophic levels in an ecosystem and the extent to which bottom–up and top–down regulation influence the biomass ratios of adjacent and non‐adjacent trophic levels (i.e. trophic cascading). We constructed an interactive model of plant (pasture), herbivore (red kangaroo Macropus rufus) and predator (dingo Canis lupus dingo), a system in which trophic cascades have been suggested to occur, and used it to test the effects of increasing stochastic variation in primary productivity and dingo culling on predictions of the EEH. The model contained four feedback loops: the predator–herbivore and herbivore–plant feedback loops, and the predator and plant density‐dependent feedback loops. The equilibrium conditions along the primary productivity gradient reproduced the three zones of trophic dynamics predicted by the EEH, plus an additional zone at productivities above which the maximum density of a predator is achieved due to social regulation: that zone is characterized by increasing herbivore density and decreasing plant biomass. Culling dingoes produced trophic cascades that were strongly attenuated at primary productivities below which the maximum density of dingoes was attained. Results were robust to uncertainty in kangaroo off‐take by dingoes and to the efficacy of dingo culling, but prey switching by dingoes from red kangaroos to reptiles would weaken trophic cascades. We conclude that social regulation of carnivores has important implications for expression of the EEH and trophic cascades, and that attenuation of trophic cascades increases with increasing stochasticity in primary productivity. Our model also provides a framework for understanding the conditions in which dingo‐mediated trophic cascades might be expected to occur, and generates testable predictions about the effects of higher dingo densities (e.g. by stopping culling or reintroduction to former range) on kangaroo and pasture dynamics.

Nabe‐Nielsen, Jacob; Tougaard, Jakob; Teilmann, Jonas; Lucke, Klaus; Forchhammer, Mads C.

doi: 10.1111/j.1600-0706.2013.00069.xpmid: N/A

Animals often alternate between searching for food locally and moving over larger distances depending on the amount of food they find. This ability to switch between movement modes can have large implications on the fate of individuals and populations, and a mechanism that allows animals to find the optimal balance between alternative movement strategies is therefore selectively advantageous. Recent theory suggests that animals are capable of switching movement mode depending on heterogeneities in the landscape, and that different modes may predominate at different temporal scales. Here we develop a conceptual model that enables animals to use either an area‐concentrated food search behavior or undirected random movements. The model builds on the animals’ ability to remember the profitability and location of previously visited areas. In contrast to classical optimal foraging models, our model does not assume food to be distributed in large, well‐defined patches, and our focus is on animal movement rather than on how animals choose between foraging patches with known locations and value. After parameterizing the fine‐scale movements to resemble those of the harbor porpoise Phocoena phocoena we investigate whether the model is capable of producing emergent home ranges and use pattern‐oriented modeling to evaluate whether it can reproduce the large‐scale movement patterns observed for porpoises in nature. Finally we investigate whether the model enables animals to forage optimally. We found that the model was indeed able to produce either stable home ranges or movement patterns that resembled those of real porpoises. It enabled animals to maximize their food intake when fine‐tuning the memory parameters that controlled the relative contribution of area concentrated and random movements.

Kelehear, Crystal; Brown, Gregory P.; Shine, Richard

doi: 10.1111/j.1600-0706.2013.00292.xpmid: N/A

The success of a biological invasion can depend upon other invasions; and in some cases, an earlier invader may fail to spread until facilitated by a second invader. Our study documents a case whereby an invasive parasite has remained patchily distributed for decades due to the fragmented nature of available hosts; but the recent arrival of a broadly distributed alternative invasive host species provides an opportunity for the parasite to expand its range considerably. At least 20 years ago, endoparasitic pentastomids (Raillietiella frenata) were brought with their native host, the invasive Asian house gecko Hemidactylus frenatus, to the port city of Darwin in tropical Australia. These geckos rarely disperse away from human habitation, restricting the transmission of their parasites to urban environments – and thus, their pentastomids have remained patchily distributed and have only been recorded in scant localities, primarily surrounding Darwin. The recent range expansion of the invasive cane toad Rhinella marina into the Darwin area has provided an alternative host for this pentastomid. Our results show that the cane toad is a competent host for Ra. frenata– toads shed fully embryonated pentastomid eggs in their faeces – and that pentastomids are now common in cane toads near Darwin. Likely reflecting the tendency for the parasite's traditional definitive host (the Asian house gecko) and only known intermediate host (the cockroach) to reside around buildings, we found the prevalence of this parasite follows an urban distribution. Because cane toads are widely distributed through urban and rural habitat and can shed viable pentastomid eggs, the toad invasion is likely to facilitate the parasite's spread across the tropics, into areas (and additional susceptible hosts) that were previously inaccessible to it.

Sridhar, Hari; Jordán, Ferenc; Shanker, Kartik

doi: 10.1111/j.1600-0706.2013.00101.xpmid: N/A

There is a growing recognition of the need to integrate non‐trophic interactions into ecological networks for a better understanding of whole‐community organization. To achieve this, the first step is to build networks of individual non‐trophic interactions. In this study, we analyzed a network of interdependencies among bird species that participated in heterospecific foraging associations (flocks) in an evergreen forest site in the Western Ghats, India. We found the flock network to contain a small core of highly important species that other species are strongly dependent on, a pattern seen in many other biological networks. Further, we found that structural importance of species in the network was strongly correlated to functional importance of species at the individual flock level. Finally, comparisons with flock networks from other Asian forests showed that the same taxonomic groups were important in general, suggesting that species importance was an intrinsic trait and not dependent on local ecological conditions. Hence, given a list of species in an area, it may be possible to predict which ones are likely to be important. Our study provides a framework for the investigation of other heterospecific foraging associations and associations among species in other non‐trophic contexts.

Camargo, Maria Gabriela G.; Cazetta, Eliana; Schaefer, H. Martin; Morellato, L. Patrícia C.

doi: 10.1111/j.1600-0706.2013.00328.xpmid: N/A

Communication contributes to mediate the interactions between plants and the animals that disperse their genes. As yet, seasonal patterns in plant–animal communication are unknown, even though many habitats display pronounced seasonality e.g. when leaves senescence. We thus hypothesized that the contrast between fruit displays and their background vary throughout the year in a seasonal habitat. If this variation is adaptive, we predicted higher contrasts between fruits and foliage during the fruiting season in a cerrado–savanna vegetation, southeastern Brazil. Based on a six‐year data base of fruit ripening and a one‐year data set of fruit biomass, we used reflectance measurements and contrast analysis to show that fruits with distinct colors differed in the beginning of ripening and the peak of fruit biomass. Black, and particularly red fruits, that have a high contrast against the leaf background, were highly seasonal, peaking in the wet season. Multicolored and yellow fruits were less seasonal, not limited to one season, with a bimodal pattern for yellow ones, represented by two peaks, one in each season. We further supported the hypothesis that seasonal changes in fruit contrasts can be adaptive because fruits contrasted more strongly against their own foliage in the wet season, when most fruits are ripe. Hence, the seasonal variation in fruit colors observed in the cerrado–savanna may be, at least partly, explicable as an adaptation to ensure high conspicuousness to seed dispersers.

Weis, Jerome J.; Post, David M.

doi: 10.1111/j.1600-0706.2012.00258.xpmid: N/A

Predation has important cascading impacts on primary producer biomass and community composition in many ecosystems. While most studies have focused on the consequences of interspecific or density differences in predators, it is recognized that phenotypic variation within species can have strong and cascading community and ecosystem consequences at lower trophic levels. In coastal New England lakes, both the presence and life history form of the zooplanktivorous fish alewife, Alosa pseudoharengus, have strong influence on the biomass, size structure and community composition of crustacean zooplankton communities. Here we test the hypothesis that alewife presence and life history will have cascading impacts on phytoplankton biomass and community composition in a mesocosm experiment that previously reported strong biomass and compositional differences of crustacean zooplankton communities among alewife treatments. We show that alewife life history led to small but statistically significant differences in phytoplankton community composition among treatments. This compositional difference was driven primarily by an increase in the density of two edible phytoplankton genera associated with lower zooplankton biomass in the anadromous alewife treatment. Our results show that intraspecific variation in a predator can have cascading effects on primary producer communities. However we did not observe significant differences in total algal biomass.

Fitzsimmons, Jay M.

doi: 10.1111/j.1600-0706.2013.00207.xpmid: N/A

The use of species’ traits is increasing in ecological research. Many studies obtain trait data from a single source, implicitly assuming the accuracy of these data. I critically evaluate this assumption by measuring agreement among sources for trait data. I evaluate inter‐source agreement for 22 traits (anatomical, behavioural, life‐history and niche‐related) among five authoritative data sources (two field guides, two atlases and one online resource) for 263 Canadian butterfly species. This represents the first quantitative comparison of trait data among field guides or atlases. Traits varied considerably in their agreement among sources. Some traits such as wingspan and overwinter stage were fairly consistent among sources, whereas other traits such as habitat breadth were remarkably inconsistent among sources. These findings call into question the reliability of research that relies on a single source for trait data. I offer several recommendations for how trait researchers can account for inter‐source variation in trait data.