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Kevin Duffy   Professor  Other 
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Kevin Duffy published an article in May 2018.
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Robert A. Copeland

213 shared publications

Baohua Gu

175 shared publications

Nannan Liu

116 shared publications

Victor A. Ferrari

113 shared publications

Hospital of the University of Pennsylvania

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Distribution of Articles published per year 
(1985 - 2018)
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27
 
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Article 0 Reads 0 Citations A lepidopteran (Imbrasia belina) might influence tree-grass balance of Colophospermum mopane savanna Kevin J. Duffy, Timothy G. O’Connor, Obiora C. Collins Published: 14 May 2018
Theoretical Ecology, doi: 10.1007/s12080-018-0379-y
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Traditional explanations of tree-grass coexistence in African savannas are based on competition between these growth forms or demographic bottlenecks of trees maintained by fire or mammalian browsers. Perturbation of their “balance” may result in an alternate system state of woody encroachment. Invertebrate herbivory has never been offered as an explanation. We developed a consumer-resource model which illustrated that annual irruptions of a lepidopteran (Imbrasia belina), known as mopane worm, can determine the tree-grass balance of semi-arid Colophospermum mopane savanna in southern Africa. Model performance was sensitive to the abundance, hence mortality, of mopane worms, owing to their complete defoliation of tree leaf biomass resulting in altered competitive relations between trees and grasses. Invertebrate herbivores have been recognized in other systems as agents for effecting a state change of host tree populations; this modeling study offers a first indication of such a role for the well-researched tree-grass relations of African savannas.
Article 0 Reads 0 Citations Global pattern of plant utilization across different organisms: Does plant apparency or plant phylogeny matter? Xiaohua Dai, Jiasheng Xu, Kevin J. Duffy, Wei Zhang, Qingyun... Published: 14 March 2017
Ecology and Evolution, doi: 10.1002/ece3.2882
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The present study is the first to consider human and nonhuman consumers together to reveal several general patterns of plant utilization. We provide evidence that at a global scale, plant apparency and phylogenetic isolation can be important predictors of plant utilization and consumer diversity. Using the number of species or genera or the distribution area of each plant family as the island “area” and the minimum phylogenetic distance to common plant families as the island “distance”, we fitted presence–area relationships and presence–distance relationships with a binomial GLM (generalized linear model) with a logit link. The presence–absence of consumers among each plant family strongly depended on plant apparency (family size and distribution area); the diversity of consumers increased with plant apparency but decreased with phylogenetic isolation. When consumers extended their host breadth, unapparent plants became more likely to be used. Common uses occurred more often on common plants and their relatives, showing higher host phylogenetic clustering than uncommon uses. On the contrary, highly specialized uses might be related to the rarity of plant chemicals and were therefore very species-specific. In summary, our results provide a global illustration of plant–consumer combinations and reveal several general patterns of plant utilization across humans, insects and microbes. First, plant apparency and plant phylogenetic isolation generally govern plant utilization value, with uncommon and isolated plants suffering fewer parasites. Second, extension of the breadth of utilized hosts helps explain the presence of consumers on unapparent plants. Finally, the phylogenetic clustering structure of host plants is different between common uses and uncommon uses. The strength of such consistent plant utilization patterns across a diverse set of usage types suggests that the persistence and accumulation of consumer diversity and use value for plant species are determined by similar ecological and evolutionary processes.
Article 0 Reads 2 Citations Model highlights likely long-term influences of mesobrowsers versus those of elephants on woodland dynamics Christopher A. J. O'Kane, Kevin J. Duffy, Bruce R. Page, Dav... Published: 12 August 2013
African Journal of Ecology, doi: 10.1111/aje.12103
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The potential long‐term influences of mesobrowsers versus those of savannah elephants on woodland dynamics have not been explored. This may be a critical omission especially in southern African savannahs, where efforts to preserve existing woodlands are typically directed at elephant management. We describe a simple browse–browser model, parameterized from an extensive review of the literature and our own data, including quantitative assessment of impala impact, from the study site, iMfolozi Park, South Africa. As there is a paucity of species‐specific demographic data on savannah woody species, we modelled, in a novel approach, functional groups of plant species typical of Acacia woodlands. Outputs suggest that over the long term (100 years), low‐to‐moderate densities of impala will have a similar impact on woodland structure, in terms of density of adult trees, as low‐to‐moderate densities of elephant. Further, the outputs highlight the apparently strong synergistic effect impala and elephant impacts combined have on woodland dynamics, suggesting that reduction or removal of either impala or elephant will radically reduce long‐term destruction of savannah woodlands. Recorded changes in adult tree numbers in iMfolozi broadly supported the model's outputs.
Article 0 Reads 6 Citations Stable isotope turnover and variability in tail hairs of captive and free-ranging African elephants ( Loxodonta africana... Kevin J. Duffy, Julia A. Lee-Thorp, Jacqueline Codron, Kevin... Published: 01 March 2013
Canadian Journal of Zoology, doi: 10.1139/cjz-2012-0155
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Many herbivore species expand their dietary niche breadths by switching from browse-rich diets in dry seasons to grass-rich diets in rainy seasons, in response to phenological changes in plant availability and quality. We analyzed stable isotope series along tail hairs of captive and free-ranging African elephant (Loxodonta africana (Blumenbach, 1797)) to compare patterns of seasonal dietary variability across individuals. Results from elephants translocated from the wild into captivity, where their diets are semicontrolled, revealed tail hair growth rates of ∼0.34 mm/day, on average, and relatively rapid isotope turnover through the transition from wild into captivity. Sampling hairs at 10 mm increments thus archives dietary chronologies at a resolution suitable for tracking diet switches at seasonal, and even subseasonal, scales. Hairs of free-ranging elephants showed extensive carbon isotopic variability within individuals, consistent with seasonal switches between C3-browsing and C4-grazing. Similarly extensive, but asynchronous, shifts in nitrogen isotope ratios were also observed, suggesting an influence of factors other than seasonality. Across individuals, switching patterns differed across habitats, and across age classes, with older, larger animals including increasing amounts of C3 browse into their diets. These results demonstrate how stable isotope approaches characterize complex patterns of resource use in wildlife populations. Many herbivore species expand their dietary niche breadths by switching from browse-rich diets in dry seasons to grass-rich diets in rainy seasons, in response to phenological changes in plant availability and quality. We analyzed stable isotope series along tail hairs of captive and free-ranging African elephant (Loxodonta africana (Blumenbach, 1797)) to compare patterns of seasonal dietary variability across individuals. Results from elephants translocated from the wild into captivity, where their diets are semicontrolled, revealed tail hair growth rates of ∼0.34 mm/day, on average, and relatively rapid isotope turnover through the transition from wild into captivity. Sampling hairs at 10 mm increments thus archives dietary chronologies at a resolution suitable for tracking diet switches at seasonal, and even subseasonal, scales. Hairs of free-ranging elephants showed extensive carbon isotopic variability within individuals, consistent with seasonal switches between C3-browsing and C4-grazing. Similarly extensive, but asynchronous, shifts in nitrogen isotope ratios were also observed, suggesting an influence of factors other than seasonality. Across individuals, switching patterns differed across habitats, and across age classes, with older, larger animals including increasing amounts of C3 browse into their diets. These results demonstrate how stable isotope approaches characterize complex patterns of resource use in wildlife populations.
Article 0 Reads 5 Citations Effects of resource limitation on habitat usage by the browser guild in Hluhluwe-iMfolozi Park, South Africa Christopher A. J. O'Kane, Kevin J. Duffy, Bruce R. Page, Dav... Published: 01 January 2013
Journal of Tropical Ecology, doi: 10.1017/s0266467413000035
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Resource depletion and associated increases in interspecific competition are likely to influence differential habitat usage amongst a guild. We tested some prominent theoretical concepts using observed differences in seasonal habitat use amongst the savanna browser guild (elephant, giraffe, impala, kudu and nyala) in Hluhluwe-iMfolozi Park, South Africa. Herbivore locations (n = 3108) were recorded over 2 y using repeated road transects and, for elephant, GPS collars (187 254 downloads). Densities were calculated using a novel GIS approach designed to be a cost-effective method for annual censuses, but also able to cope with abrupt changes in visibility. Selectivity for (Manly's α) vegetation types, and overlap (Schoener's index) in vegetation type usage were calculated. Resource depletion in the dry season resulted in all members of the guild increasing selectivity for vegetation types (sum of absolute values away from the neutral value for Manly's alpha for the guild: dry seasons 3.97, 5.16; corresponding wet seasons 3.12, 3.68), but decreasing interspecific overlap (80% of Schoener's indices lower in dry season versus wet season). These effects were more marked over the second, more severe, dry season. We found support for the niche overlap hypothesis and the niche compression hypothesis. The Jarman–Bell principle was generally supported, although unexpectedly during the severe dry season elephant showed the most selectivity for vegetation type. The greater the resource depletion, the more relevant interspecific differences in habitat usage become in relation to the differential impacts of guild members.
Article 0 Reads 15 Citations Preischemic targeting of HIF prolyl hydroxylation inhibits fibrosis associated with acute kidney injury P. P. Kapitsinou, M. Michael, C. E. Swan, K. J. Duffy, C. L.... Published: 01 May 2012
American Journal of Physiology-Renal Physiology, doi: 10.1152/ajprenal.00667.2011
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Acute kidney injury (AKI) due to ischemia is an important contributor to the progression of chronic kidney disease (CKD). Key mediators of cellular adaptation to hypoxia are oxygen-sensitive hypoxia-inducible factors (HIF), which are regulated by prolyl-4-hydroxylase domain (PHD)-containing dioxygenases. While activation of HIF protects from ischemic cell death, HIF has been shown to promote fibrosis in experimental models of CKD. The impact of HIF activation on AKI-induced fibrosis has not been defined. Here, we investigated the role of pharmacologic HIF activation in AKI-associated fibrosis and inflammation. We found that pharmacologic inhibition of HIF prolyl hydroxylation before AKI ameliorated fibrosis and prevented anemia, while inhibition of HIF prolyl hydroxylation in the early recovery phase of AKI did not affect short- or long-term clinical outcome. Therefore, preischemic targeting of the PHD/HIF pathway represents an effective therapeutic strategy for the prevention of CKD resulting from AKI, and it warrants further investigation in clinical trials.