Podani J.,Hungarian Academy of Sciences |
Schmera D.,University of Basel |
Schmera D.,Balaton Limnological Research Institute
Ecography | Year: 2012
This paper deals with nestedness measures that are based on pairwise comparisons of sites, evaluates their performance and suggests improvements and generalizations. There are several conceptual and technical criteria to judge their ecological applicability. It is of primary concern whether the measures 1) have a clear mathematical definition, 2) are influenced by the ordering of the data matrix, 3) incorporate similarity alone or similarity together with a dissimilarity component, 4) consider site pairs with identical species number negatively or positively, 5) show sensitivity to small changes in the data, and 6) are not vulnerable to type I and type II error rates. We performed a detailed comparison of the nestedness metric based on overlap and decreasing fill (NODF), the percentage relativized nestedness and the percentage relativized strict nestedness functions (PRN and PRSN, respectively), based on analytical results as well as on artificial and actual examples. We show that NODF is in fact the average Simpson similarity of sites with different species totals, and that its value depends on how the matrix is actually ordered. NODF is modified to always produce the maximum possible result (NODF max), independently of the order of columns and rows. Being based on similarities, NODF and NODF max overemphasize the overlap component of nestedness and underrate richness difference which is also an important constituent of nested pattern in meta-community data. This latter feature is reflected adequately by PRN and PRSN. However, PRSN is similar to NODF and NODF max in sharing the disadvantages that 1) complete agreement and segregation in species composition are not distinguished, 2) a random matrix can have a higher value than truly nested patterns, and 3) they are ill-conditioned statistically. These problems are rooted mostly in that site pairs with tied totals affect the result negatively. We emphasize that PRN is free from these difficulties. PRN, PRSN, and NODF max, together with mean Simpson similarity exhibit highly similar statistical performance: they are resistant to type I and type II errors for the less constrained null models, although there are subtle differences depending on matrix fill and algorithm of randomization. The most constrained null model, with all marginal totals fixed, makes all statistics more sensitive to type I errors, although vulnerability depends greatly on matrix fill. © 2012 The Authors.
Eros T.,Balaton Limnological Research Institute |
Campbell Grant E.H.,U.S. Geological Survey
Freshwater Biology | Year: 2015
While there is an increasing emphasis in terrestrial ecology on determining the influence of the area that surrounds habitat patches (the landscape 'matrix') relative to the characteristics of the patches themselves, research on these aspects in running waters is still rather underrepresented. Here we outline conceptual foundations of matrix ecology for stream and river ecosystems ('riverscapes'). We discuss how a hierarchical, patch-based perspective is necessary for the delineation of habitat patches and the surrounding matrix, through which we may identify two classes of habitat edges in riverscapes (i.e. edges between the terrestrial-aquatic interface and edges within streams). Under this conceptual framework, we discuss the role of the matrix in influencing between-patch movement, and resource quality and quantity within and among habitat patches in riverscapes. We also review types of empirical and modelling approaches which may advance our understanding of fragmentation effects in these systems. We identify five key challenges for understanding fragmentation and matrix effects more completely: (i) defining populations and their status (i.e. quantifying the demographic contribution of habitat patches to metapopulation dynamics), (ii) scaling from metapopulations to metacommunities (particularly searching for generalities in species responses to landscape heterogeneity), (iii) scaling from metacommunities to metaecosystems (i.e. exploring the interactive role of the terrestrial-aquatic and within-stream matrix effects on the flow of material and energy at the network scale), (iv) understanding temporal dynamics in matrix permeability and (v) revealing the utility of different patch and matrix representations for modelling connectivity relationships. Fragmentation of habitats is a critical issue in the conservation and management of stream networks across spatial scales. Although the effects of individual barriers (e.g. dams) are well documented, we argue that a more comprehensive patch-matrix landscape model will improve our understanding of fragmentation effects and improve management in riverscapes. © 2015 John Wiley & Sons Ltd.
Specziar A.,Balaton Limnological Research Institute
Journal of Fish Biology | Year: 2011
Prey size and species selection of pikeperch Sander lucioperca and Volga pikeperch Sander volgensis were investigated in relation to predator size in the shallow Lake Balaton, Hungary. Although their gape sizes were similar, S. lucioperca shifted to piscivory earlier and consumed fewer, but larger, prey than S. volgensis. Prey species preference of the two piscivores also differed. A bimodal prey size distribution resulted in a reclining sigmoid curve for the life span predator size to prey size relationship with inflexion points between 266 and 284 mm predator standard length (L S) in S. lucioperca. In S. volgensis, as well as in S. lucioperca L S≤ 350 mm, prey size increased monotonically with predator L S, following a power trend for all prey size variables. Prey depth to predator L S relationship varied significantly with prey species and prey number in both piscivores, and prey depth tended to be smaller in predators consuming more than one prey. Both predator species characteristically selected less active, benthic prey fishes in spite of their spiny fin rays, and small- and mid-sized predators selected for small prey. Relatively large prey were also eaten, however, especially by the smallest and largest S. lucioperca. © 2011 The Author. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.
Kiss T.,Balaton Limnological Research Institute
General and Comparative Endocrinology | Year: 2011
Neuropeptides, the most diverse group of signaling molecules, are responsible for regulating a variety of cellular and behavioral processes in all vertebrate and invertebrate animals. The role played by peptide signals in information processing is fundamentally different from that of conventional neurotransmitters. Neuropeptides may act as neurotransmitters or neuromodulators and are released at either synaptic or non-synaptic sites. Peptide signals control developmental processes, drive specific behaviors or contribute to the mechanisms of learning and memory storage. Co-transmission within or across peptide families, and between peptide and non-peptide signaling molecules, is common; this ensures the great versatility of their action. How these tasks are fulfilled when multiple neuropeptides are released has become an important topic for peptide research. Although our knowledge concerning the physiological and behavioral roles of most of the neuropeptides isolated from molluscs is incomplete, this article provides examples to address the complexity of peptide signaling. © 2011.
Podani J.,A.P.S. University |
Schmera D.,University of Basel |
Schmera D.,Balaton Limnological Research Institute
Oikos | Year: 2011
A conceptual framework is proposed to evaluate the relative importance of beta diversity, nestedness and agreement in species richness in presence - absence data matrices via partitioning pairwise gamma diversity into additive components. This is achieved by calculating three complementary indices that measure similarity, relative species replacement, and relative richness difference for all pairs of sites, and by displaying the results in a two-dimensional simplex diagram, or ternary plot. By summing two terms at a time, three one-dimensional simplices are derived correspondig to different contrasts: beta diversity versus similarity, species replacement versus nestedness and, finally, richness difference versus richness agreement. The simplex diagrams can be used to interpret underlying data structures by showing departure from randomness towards well-interpretable directions, as demonstrated by artificial and actual examples. In particular, one may appreciate how far data structure deviates from three extreme model situations: perfect nestedness, anti-nestedness and perfect gradient. Throughout the paper, we pay special attention to the measurement and interpetation of beta diversity and nestedness for pairs of sites, because these concepts have been in focus of ecological reseach for decades. The novel method can be used in community ecology, conservation biology, and biogeography, whenever the objective is to recover explanatory ecological processes behind patterns conveyed by presence-absence data. © 2011 The Authors.