Browsing by Author "Hui C."
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- ItemAn interaction switch predicts the nested architecture of mutualistic networks(2011) Zhang F.; Hui C.; Terblanche J.S.Nested architecture is distinctive in plant-animal mutualistic networks. However, to date an integrative and quantitative explanation has been lacking. It is evident that species often switch their interactive partners in real-world mutualistic networks such as pollination and seed-dispersal networks. By incorporating an interaction switch into a novel multi-population model, we show that the nested architecture rapidly emerges from an initially random network. The model allowing interaction switches between partner species produced predictions which fit remarkably well with observations from 81 empirical networks. Thus, the nested architecture in mutualistic networks could be an intrinsic physical structure of dynamic networks and the interaction switch is likely a key ecological process that results in nestedness of real-world networks. Identifying the biological processes responsible for network structures is thus crucial for understanding the architecture of ecological networks. © 2011 Blackwell Publishing Ltd/CNRS.
- ItemEstimating changes in species abundance from occupancy and aggregation(2012) Hui C.; Boonzaaier C.; Boyero L.Predicting the change in abundance is pivotal for evaluating species' current conservation status and population viability. Empirical works have suggested that species with an increasing abundance have a more aggregated distribution than those with a declining abundance (namely, the change-aggregation hypothesis, CAH). Here we introduced an improved negative binomial distribution model of the occupancy-abundance relationship (OAR) to estimate the change in abundance from changes in occupancy or aggregation. Analysis of the model suggests that (i) in general the change in abundance is synchronized with the change in occupancy when the level of environmental heterogeneity remains constant, and (ii) there could exist a threshold of the population density above which the CAH is no longer valid. Tests using data of epigaeic ants in Fynbos of South Africa collected from different seasons and macro-invertebrates from different localities in streams of central Spain verified these model propositions and thus support the use of this model as a monitoring method for assessing species persistence. Results suggest that the change in abundance can be estimated from the change in occupancy often obtained from cost-efficient presence-absence records, and a revision of the traditional CAH is necessary to capture the threshold phenomenon in the change-aggregation relationship. This work thus signifies the use of the three distinct but related concepts of population structure (i.e. occupancy, abundance and aggregation) in conservation biology. © 2012 Gesellschaft für ökologie.
- ItemFrom the Inverse Density-Area Relationship to the Minimum Patch Size of a Host-Parasitoid System(2012) Zhao Z.-H.; He D.-H.; Hui C.The minimum amount of suitable habitat (MASH) is an important concept in conservation biological control. Two methods for estimating the MASH have been proposed by McCoy and Mushinsky based on an inverse density-area relationship. Using data of the population densities of aphid host-parasitoid-hyperparasitoid collected from wheat fields of different habitat sizes, we argued that the inverse density-area relationship may be an artifact. Significant correlations between population densities and patch sizes from all three trophic levels were found once the population density had been log-transformed. We could not obtain the same results if the population density had not been log-transformed. We estimated that the MASH for the aphid M. avena, S. graminum, A. avenae, A. gifuensis, P. aphidis, and Alloxysta sp. were 246, 246, 479, 495, 949, and 835 m 2 according to the methods of McCoy and Mushinsky. The scale-dependence and the systematic spatial variations of the host-parasitoid interaction suggests that we can achieve an optimal effect of biological control by manipulating the habitat patch sizes, although not based on the inverse density-area relationship. © 2011 The Ecological Society of Japan.
- ItemImportance of primary metabolites in canola in mediating interactions between a specialist leaf-feeding insect and its specialist solitary endoparasitoid(2012) Soufbaf M.; Fathipour Y.; Zalucki M.P.; Hui C.The role of primary plant chemistry on trophic interactions is not well studied. We examined the effect of primary plant metabolites, focusing on nitrogen, on several biological indices of second and third trophic level insects in a model tritrophic system, consisting of two strains of the crucifer, Brassicanapus (canola) (SLM 046 and RGS 003), the specialist insect herbivore Plutella xylostella (L.) (Lepidoptera: Plutellidae), and its specialist koinobiont larval-pupal parasitoid Diadegma semiclausum (Hellén) (Hymenoptera: Ichneumonidae). In particular, we measured relative growth rate of the herbivore in relation to an index for plant quality (nitrogen content of leaf tissues), developmental time of the herbivore (sum of second, third, and fourth larval instars durations), and intrinsic rate of increase (r m) of the herbivore and the parasitoid. Tritrophic studies were conducted on development, survivorship curve analysis, reproductive potential, life history, parasitism, and several other fitness correlates of the parasitoid. The life table parameters of D. semiclausum were determined under laboratory conditions. The intrinsic rate of increase (r m) of the parasitoid was significantly higher on RGS 003 than SLM 046. In this tritrophic model, the results indicated that the bottom-up direct effect on the herbivore population growth rate was marginally as strong as the direct effect of top-down force due to the parasitoid population growth rate; but it was higher than its indirect counterpoint mediated with the parasitoid population growth rate. Consequently, D. semiclausum performed better on RGS 003, which was the most inferior host to P. xylostella in comparison with another plant cultivar and had the lowest content of nitrogen in its leaves. © 2012 Springer Science+Business Media B.V.
- ItemOn the scaling patterns of species spatial distribution and association(2009) Hui C.Understanding how species distribution (occupancy and spatial autocorrelation) and association (that is, multi-species co-distribution) change across scales is fundamental to unlocking the pattern formation in population ecology and macroecology. Based on the Bayesian rule and join-count statistics, I present here a mathematical model that can demonstrate the effect of spatial scale on the observation of species distribution and association. Results showed that the intensity of spatial autocorrelation and species association declines when the grain in the spatial analysis increases, although the category of species distribution (aggregated or segregated) and association (positive or negative) remains the same. Random distribution and species independence were proved to be scale-free. Regardless of the possible patterns of species distribution and association, species tend to be randomly distributed and independent from each other when scaling-up (an increasing grain), reflecting a percolation process. This model, thus, grasps the statistical essence of species scaling pattern and presents a step forward for unveiling mechanisms behind species distributional and macroecological patterns. © 2009 Elsevier Ltd. All rights reserved.
- ItemRelative roles of climatic suitability and anthropogenic influence in determining the pattern of spread in a global invader(2011) Roura-Pascual N.; Hui C.; Ikeda T.; Leday G.; Richardson D.M.; Carpintero S.; Espadaler X.; Gomez C.; Guenard B.; Hartley S.; Krushelnycky P.; Lester P.J.; McGeoch M.A.; Menke S.B.; Pedersen J.S.; Pitt J.P.W.; Reyes J.; Sanders N.J.; Suarez A.V.; Touyama Y.; Ward D.; Ward P.S.; Worner S.P.Because invasive species threaten the integrity of natural ecosystems, a major goal in ecology is to develop predictive models to determine which species may become widespread and where they may invade. Indeed, considerable progress has been made in understanding the factors that influence the local pattern of spread for specific invaders and the factors that are correlated with the number of introduced species that have become established in a given region. However, few studies have examined the relative importance of multiple drivers of invasion success for widespread species at global scales. Here, we use a dataset of >5,000 presence/absence records to examine the interplay between climatic suitability, biotic resistance by native taxa, human-aided dispersal, and human modification of habitats, in shaping the distribution of one of the world's most notorious invasive species, the Argentine ant (Linepithema humile). Climatic suitability and the extent of human modification of habitats are primarily responsible for the distribution of this global invader. However, we also found some evidence for biotic resistance by native communities. Somewhat surprisingly, and despite the often cited importance of propagule pressure as a crucial driver of invasions, metrics of the magnitude of international traded commodities among countries were not related to global distribution patterns. Together, our analyses on the global-scale distribution of this invasive species provide strong evidence for the interplay of biotic and abiotic determinants of spread and also highlight the challenges of limiting the spread and subsequent impact of highly invasive species.
- ItemScale effect and bimodality in the frequency distribution of species occupancy(2012) Hui C.Community patterns in species-by-site matrices provide valuable clues for inferring ecological processes at work. One such pattern is the occupancy frequency distribution (OFD) depicting the frequency distribution of row sums (i.e., occupancy) with a quarter OFDs of bimodal forms. Another pattern that also reflects the structure of row sums is the ranked species occupancy curve (RSOC), and has been shown to imply a 50% of bimodality in OFDs. The use of RSOCs has been advocated in literature over the OFD based on two conclusions from a 6-model inference using only 24 matrices: (i) RSOCs have two general forms, with half representing bimodal OFDs; (ii) there are no effects of spatial and study scales on RSOCs of different forms. Using a much more representative dataset of 289 matrices, I cast doubt on these two conclusions. A missing but dominant RSOC model (the truncated power law) is added. The number of species and the nestedness of the community differ significantly among matrices of different RSOC forms; however, the number of sites and the taxa in the studies do not differ among RSOC or OFD forms. The quarter OFDs of bimodal forms is reassured, with the least frequent occupancy consistent with Raunkiaer's law of frequency. Importantly, a RSOC is mathematically transferrable to an OFD, with the derivative of the occupancy ranking curve being equal to the negative reciprocal of the occupancy frequency. Based on the type of the community (null versus interactive) and site environment (homogenous versus heterogeneous), four scenarios are needed to identify pre-inferring assemblage mechanisms. The results highlight the need for shifting research from the emphasis of marginal sums to the analysis of matrix structure for an in-depth understanding of the community assemblage patterns and mechanisms.
- ItemSpatially-explicit sensitivity analysis for conservation management: Exploring the influence of decisions in invasive alien plant management(2010) Roura-Pascual N.; Krug R.M.; Richardson D.M.; Hui C.Aim: Decision-support models have considerable potential for guiding management strategies when problems are complex. The robustness of such decision-making processes is rarely evaluated, and the influence of decision criteria (or factors) in management decisions is seldom considered. We present a framework for a spatially-explicit sensitivity analysis by using a scheme developed to provide objective guidelines, in the form of static priority maps, for managing woody invasive alien plants (IAPs). Location: The Cape Floristic Region, South Africa. Methods: The model included seven factors related to management history, fire risk, and the age, identity, density and spread of IAPs. Each factor had a weight associated that reflected its relative importance in prioritizing areas for clearing. We changed these factor weights using three approaches of sensitivity analysis and assessed the effect of these changes on the spatial structure of the resulting priority maps in three different management regions. Results: Different outcomes arose depending on the importance given to different factors. Priority maps were most sensitive to the fire-related factors, suggesting that fire is both a crucial driver of invasion in fynbos and an overriding determinant of management options. The factor 'area burnt recently' provided crucial information for the effective clearing of IAPs. The sensitivity of the model to changes in other factors was more context specific: levels of sensitivity were highly dependent on different features of the landscape, especially the spatial heterogeneity of particular factors. Main conclusions: By clarifying the importance of factors in shaping priority maps, the sensitivity analysis framework enabled us to identify the necessary factors to produce outcomes matching a pre-selected management strategy. This is important for cost-efficient management, as acquisition and curation of data is expensive. This spatially-explicit sensitivity analysis is, thus, recommended to evaluate the robustness and generality of selected management strategies, and validate the assumptions derived from decision-making protocols. © 2010 Blackwell Publishing Ltd.