Plant communities and food webs

Recent theoretical work has provided major new insights into the ways that species interactions in food webs are organized in ways that permit the coexistence of significant numbers of species. But, we seem to have forgotten about trees! Not the phylogenetic ones that are increasingly important for dissecting the evolutionary structure of food webs, but the trees, shrubs and grasses that are the basal species in all terrestrial ecosystems. Many of the food webs available for analysis over the last 30 years were based on freshwater or marine systems where algae were the main plants. Trees are very different from algae; they can live for centuries, while annually producing leaves, fruits and seeds that provide nutrients for a diversity of species on higher trophic levels. In sharp contrast to algae, they are only partly consumed by herbivores and usually compensate or recover from herbivory. Most of the biomass in terrestrial systems is in the plants, this again contrasts with aquatic systems, where most of the biomass is in primary and secondary consumers. Moreover, each individual tree supports its own food web of species that are only partially coupled to those of surrounding trees. If we are going to apply our theoretical understanding of food-web structure to species-rich terrestrial ecosystems in ways that are insightful for conservation, then we need a deeper examination of the role that higher plants play in food webs. While community ecology has developed an increasingly detailed understanding of the ways plant communities are organized, this seems to have evolved almost independently of the food-web literature. In this article, we make a plea to more sharply consider higher plants in food webs and to do this by combining recent theoretical work on food webs, with recent empirical and theoretical work on plant communities. Ultimately, we argue for a deeper integration of plant community ecology into studies of food webs

Where Are the Parasites? [Letters]

First paragraph: The review by E. Post et al. ( Ecological dynamics across the Arctic associated with recent climate change, 11 September 2009, p. 1,355) paid little heed to parasites and other pathogens. The rapidly growing literature on parasites in arctic and subarctic ecosystems provides empirical and observational evidence that climate-linked changes have already occurred. The life cycle of the protostrongylid lungworm of muskoxen, Umingmakstrongylus pallikuukensis, has changed, and the range of that organism and the winter tick, Dermacentor albipictus, has expanded

Where Are the Parasites? [Letters]

First paragraph: The review by E. Post et al. ( Ecological dynamics across the Arctic associated with recent climate change, 11 September 2009, p. 1,355) paid little heed to parasites and other pathogens. The rapidly growing literature on parasites in arctic and subarctic ecosystems provides empirical and observational evidence that climate-linked changes have already occurred. The life cycle of the protostrongylid lungworm of muskoxen, Umingmakstrongylus pallikuukensis, has changed, and the range of that organism and the winter tick, Dermacentor albipictus, has expanded

Gray Wolves as Climate Change Buffers in Yellowstone

Understanding the mechanisms by which climate and predation patterns by top predators co-vary to affect community structure accrues added importance as humans exert growing influence over both climate and regional predator assemblages. In Yellowstone National Park, winter conditions and reintroduced gray wolves (Canis lupus) together determine the availability of winter carrion on which numerous scavenger species depend for survival and reproduction. As climate changes in Yellowstone, therefore, scavenger species may experience a dramatic reshuffling of food resources. As such, we analyzed 55 y of weather data from Yellowstone in order to determine trends in winter conditions. We found that winters are getting shorter, as measured by the number of days with snow on the ground, due to decreased snowfall and increased number of days with temperatures above freezing. To investigate synergistic effects of human and climatic alterations of species interactions, we used an empirically derived model to show that in the absence of wolves, early snow thaw leads to a substantial reduction in late-winter carrion, causing potential food bottlenecks for scavengers. In addition, by narrowing the window of time over which carrion is available and thereby creating a resource pulse, climate change likely favors scavengers that can quickly track food sources over great distances. Wolves, however, largely mitigate late-winter reduction in carrion due to earlier snow thaws. By buffering the effects of climate change on carrion availability, wolves allow scavengers to adapt to a changing environment over a longer time scale more commensurate with natural processes. This study illustrates the importance of restoring and maintaining intact food chains in the face of large-scale environmental perturbations such as climate change

Assessing the burden of pregnancy-associated malaria under changing transmission settings

BACKGROUND: The clinical presentation of pregnancy-associated malaria, or PAM, depends crucially on the particular epidemiological settings. This can potentially lead to an underestimation of its overall burden on the female population, especially in regions prone to epidemic outbreaks and where malaria transmission is generally low. METHODS: Here, by re-examining historical data, it is demonstrated how excess female mortality can be used to evaluate the burden of PAM. A simple mathematical model is then developed to highlight the contrasting signatures of PAM within the endemicity spectrum and to show how PAM is influenced by the intensity and stability of transmission. RESULTS: Both the data and the model show that maternal malaria has a huge impact on the female population. This is particularly pronounced in low-transmission settings during epidemic outbreaks where excess female mortality/morbidity can by far exceed that of a similar endemic setting. CONCLUSION: The results presented here call for active intervention measures not only in highly endemic regions but also, or in particular, in areas where malaria transmission is low and seasonal

Impacts of neighbourhood planning in England

Prof. Gavin Parker (University of Reading) Dr Matthew Wargent (University of Reading) Dr Kat Salter (University of Birmingham) Dr Mark Dobson (University of Reading) Dr Tessa Lynn (University of Reading) Dr Andy Yuille (Lancaster University) and Navigus Plannin

Climate forcing and desert malaria: the effect of irrigation

BACKGROUND: Rainfall variability and associated remote sensing indices for vegetation are central to the development of early warning systems for epidemic malaria in arid regions. The considerable change in land-use practices resulting from increasing irrigation in recent decades raises important questions on concomitant change in malaria dynamics and its coupling to climate forcing. Here, the consequences of irrigation level for malaria epidemics are addressed with extensive time series data for confirmed Plasmodium falciparum monthly cases, spanning over two decades for five districts in north-west India. The work specifically focuses on the response of malaria epidemics to rainfall forcing and how this response is affected by increasing irrigation. METHODS AND FINDINGS: Remote sensing data for the Normalized Difference Vegetation Index (NDVI) are used as an integrated measure of rainfall to examine correlation maps within the districts and at regional scales. The analyses specifically address whether irrigation has decreased the coupling between malaria incidence and climate variability, and whether this reflects (1) a breakdown of NDVI as a useful indicator of risk, (2) a weakening of rainfall forcing and a concomitant decrease in epidemic risk, or (3) an increase in the control of malaria transmission. The predictive power of NDVI is compared against that of rainfall, using simple linear models and wavelet analysis to study the association of NDVI and malaria variability in the time and in the frequency domain respectively. CONCLUSIONS: The results show that irrigation dampens the influence of climate forcing on the magnitude and frequency of malaria epidemics and, therefore, reduces their predictability. At low irrigation levels, this decoupling reflects a breakdown of local but not regional NDVI as an indicator of rainfall forcing. At higher levels of irrigation, the weakened role of climate variability may be compounded by increased levels of control; nevertheless this leads to no significant decrease in the actual risk of disease. This implies that irrigation can lead to more endemic conditions for malaria, creating the potential for unexpectedly large epidemics in response to excess rainfall if these climatic events coincide with a relaxation of control over time. The implications of our findings for control policies of epidemic malaria in arid regions are discussed

Spatial Guilds in the Serengeti Food Web Revealed by a Bayesian Group Model

Food webs, networks of feeding relationships in an ecosystem, provide fundamental insights into mechanisms that determine ecosystem stability and persistence. A standard approach in food-web analysis, and network analysis in general, has been to identify compartments, or modules, defined by many links within compartments and few links between them. This approach can identify large habitat boundaries in the network but may fail to identify other important structures. Empirical analyses of food webs have been further limited by low-resolution data for primary producers. In this paper, we present a Bayesian computational method for identifying group structure using a flexible definition that can describe both functional trophic roles and standard compartments. We apply this method to a newly compiled plant-mammal food web from the Serengeti ecosystem that includes high taxonomic resolution at the plant level, allowing a simultaneous examination of the signature of both habitat and trophic roles in network structure. We find that groups at the plant level reflect habitat structure, coupled at higher trophic levels by groups of herbivores, which are in turn coupled by carnivore groups. Thus the group structure of the Serengeti web represents a mixture of trophic guild structure and spatial pattern, in contrast to the standard compartments typically identified. The network topology supports recent ideas on spatial coupling and energy channels in ecosystems that have been proposed as important for persistence. Furthermore, our Bayesian approach provides a powerful, flexible framework for the study of network structure, and we believe it will prove instrumental in a variety of biological contexts.</p

Seasonal Patterns of Infectious Diseases

Why is that many infectious diseases, like cholera, malaria, and meningococcal meningitis, show seasonal patterns? And how can we accurately determine these patterns

Accelerating climate action: the role of health professionals.

Editorial - No abstract available