Food Web Dynamics

Uncertainty vs parsimony in food web research

by Debal Deb

Widespread crown condition decline, food web disruption and amplified tree mortality with increased climate-change-type drought

by Jofre Carnicer

published in PNAS, 2011

Climate change is progressively increasing severe drought events in the Northern Hemisphere, causing regional tree... more Climate change is progressively increasing severe drought events in the Northern Hemisphere, causing regional tree die-off events and contributing to the global reduction of carbon sink efficiency of forests. There is a critical lack of integrated community-wide assessments of drought-induced responses in forests at the macroecological scale, including defoliation, mortality and food web responses. Here we report a generalized increase in crown defoliation in southern European forests during 1987-2007. Forest tree species have consistently and significantly altered their crown leaf structures, showing increased percentages of defoliation in the drier parts of their distributions in response to increased water deficit. The demographic responses of trees associated with increased defoliation in Southern European forests are specifically assessed in the Iberian Peninsula region. We observe that defoliation trends are paralleled by significant increases in tree mortality rates in drier areas, which are related to tree density and temperature effects. Furthermore, we show that severe drought impacts are associated with sudden changes in insect and fungal defoliation dynamics, creating long-term disruptive effects of drought on food webs. Our results reveal a complex geographical mosaic of species-specific responses to climate-change driven drought pressures on the Iberian Peninsula, with an overwhelmingly predominant trend towards increased drought damage.

The temporal dynamics of resource use by frugivorous birds: a network approach.

by Jofre Carnicer

published in Ecology

Ecological networks patterns are influenced by a diverse array of ecological processes that operate at different... more Ecological networks patterns are influenced by a diverse array of ecological processes that operate at different temporal scales. Here we analyzed if the coupled effect of local abundance variation, seasonally phenotypic plastic responses and species evolutionary adaptations might act in concert to shape network patterns. We studied the temporal variation in three interaction properties of bird species (number of interactions per species, interaction strength and asymmetry) in a temporal sequence of 28 plant-frugivore interaction networks spanning two years in a Mediterranean scrub community. Three main hypotheses dealing with the temporal variation of networks properties were tested, examining the effects of abundance, switching behaviour between alternative resources and morphological traits in determining consumer interaction patterns. Our results demonstrate that temporal variation in consumer interaction patterns is explained by short-term variation in resource and bird abundances and seasonal dietary switches between alternative resources (fleshy fruits and insects). Moreover, differences in beak morphology are associated with differences in switching behaviour between resources, suggesting an important role of foraging adaptations in determining network patterns. We argue that beak shape adaptations might determine generalist and specialist feeding behaviours and thus the positions of consumer species within the network. Finally, we provide a preliminary framework to interpret phylogenetic signal in plant-animal networks. Indeed, we show that the strength of the phylogenetic signal in networks depends on the relative importance of abundance, behavioural and morphological variables. We show that these variables strongly differ in their phylogenetic conservatism. Consequently, we suggest that moderate and significant phylogenetic effects should be commonly observed in networks.

Switching behavior, coexistence and diversification: comparing empirical community-wide evidence with theoretical predictions

by Jofre Carnicer

published in Ecology Letters

A primary goal for ecologists is the identification of the structures and processes that generate diversity in natural... more A primary goal for ecologists is the identification of the structures and processes that generate diversity in natural communities. Theory shows that behavioral switching between two alternative resources can increase diversity, both by enhancing species coexistence and increasing lineage diversification in mathematical models. However, an empirical demonstration of the community-wide patterns of switching predicted by this theory is still lacking. Here we evaluate the nature of switching behavior between two alternative resource channels, invertebrates and fruits, in a Mediterranean scrubland bird community.  We also examine morphological differences in a trait related to the use of these channels. Our results are the first community-wide empirical evidence showing that different patterns of resource switching that correlate with morphological differences characterize a group of potentially competing species.  These patterns are consistent with theoretical predictions, suggesting a possible role of switching behavior in promoting avian coexistence and diversification.

Long-term dynamics of a well-characterised food web: Four decades of acidification and recovery in the broadstone stream model system

by Stephen Rossiter

Wild vs. Farmed: Metal Concentration, Biomagnification and Bioaccumulation Trends in the Food Web of Qiandao Hu reservoir, China

by Matthew Ponsford

85-page honours thesis co-authored with Dr. Linda M. Campbell, Canada Research Chair (Tier II) in Aquatic Ecosystem Health, Department of Biology/Department of Environmental Studies and Dr. Yuxiang Wang, Department of Biology (Queen's University, 2010)

Natural and anthropogenic elemental contamination is widespread in the environment. This is especially true in China,... more Natural and anthropogenic elemental contamination is widespread in the environment. This is especially true in China, a country with rapid industrial and economic growth. Some metals can be toxic at very low concentrations, rapidly accumulating within fish tissues and other organisms. As fish are an important part of the Chinese diet, food web transfer and biomagnification trends of As, Cd, Co, Cr, Cu, K, Ni, Pb, Rb, Se and Zn are assessed for fish from a reservoir in eastern China. This study site, with 1,078 islands and prized freshwater fish species, contains 13 families and 86 fish species. Commonly-consumed farmed fish from a range of trophic levels were sampled, including Silurus asotus, Aristichthys nobilis, Ictalurus punctatus, Carassius auratus, Ctenopharyngodon idella, Micropterus salmoides and Hypothalmichthys molitrix. Wild piscivorous fish sampled include Siniperca chuatsi, Erythroculter mongolicus, Erythroculter illishaeformis and Channa argus argus. Our questions for this study are: (1) Are metal accumulation trends and concentrations in wild versus farmed fish species different? (2) Do trends in metal concentration between fish markets in a large city and a fishing town differ? Concentrations of Cd, Co and Pb were below reliable ICP-OES detection limits. As, Cu and Zn concentrations were highest in farmed species, whereas Cr, K, Ni, Rb and Se were highest in wild species. δ15N values were used to estimate trophic position. Results obtained suggest significant biomagnification of Se at successive trophic levels and marginally significant biomagnification trends for Rb. All other relationships between elemental concentration and trophic position indicated a lack of biomagnification. Anthropogenic sources from industrial activities surrounding the reservoir may contribute to elevated Cr and Se in fish, while ambient pH and temperature differentials could play a role in the increased bioavailability of Rb in the region.

Occurrence of okadaic acid in the feeding grounds of dugongs (Dugong dugon) and green turtles (Chelonia mydas) in Moreton Bay, Australia

by Karen Arthur

Chemical defenses: from compounds to communities

by Karen Arthur

Prey abundance and prey selection by tigers (Panthera tigris) in a semi-arid, dry deciduous forest in western India

by Sumanta Bagchi

Journal of Zoology 260: 285-290. (2003)

Food habits of tigers Panthera tigris in terms of prey abundance were studied in the semi-arid deciduous forests of... more Food habits of tigers Panthera tigris in terms of prey abundance were studied in the semi-arid deciduous forests of Ranthambhore National Park, western India, between November 2000 and April 2001. Wild prey availability was assessed by line transects (n = 8) and prey selection by the tigers was determined from analysis of scats (n = 109). Compared to some other parts of the country, prey abundance was found to be high at 96.65 animals km^−2. Chital Axis axis was the most abundant wild prey in the study area, followed by common langur Presbytis entellus, sambar Cervus unicolor, nilgai Boselaphus tragocamelus, wild pig Sus scrofa and chinkara Gazella bennetti. Chital (c. 31%) and sambar (c. 47%) constituted the bulk of the tigers’ diet and were preferred prey. Nilgai and chinkara contributed minimally to the tigers’ diet (c. 5–7% and < 1%, respectively) and were used less than their availability. Domestic livestock made up 10–12% of the tigers’ diet. The average weight of an animal consumed was between 107 and 114 kg reflecting a preference for large prey. The analysis reveals that parts of Ranthambhore have high prey abundance, thus making it important for long-term tiger conservation. Despite the high prey abundance, tigers were still considerably dependent on domestic livestock, posing challenges for the park management to resolve potential areas of conflict.