1. Understanding the structure of ecological networks is a crucial task for interpreting community and ecosystem responses to global change. 2. Despite the recent interest in this subject, almost all ...studies have focused exclusively on one specific network property. The question remains as to what extent different network properties are related and how understanding this relationship can advance our comprehension of the mechanisms behind these patterns. 3. Here, we analysed the relationship between nestedness and modularity, two frequently studied network properties, for a large data set of 95 ecological communities including both plant-animal mutualistic and host-parasite networks. 4. We found that the correlation between nestedness and modularity for a population of random matrices generated from the real communities decreases significantly in magnitude and sign with increasing connectance independent of the network type. At low connectivities, networks that are highly nested also tend to be highly modular; the reverse happens at high connectivities. 5. The above result is qualitatively robust when different null models are used to infer network structure, but, at a finer scale, quantitative differences exist. We observed an important interaction between the network structure pattern and the null model used to detect it. 6. A better understanding of the relationship between nestedness and modularity is important given their potential implications on the dynamics and stability of ecological communities.
Animal-mediated seed dispersal is important for sustaining biological diversity in forest ecosystems, particularly in the tropics. Forest fragmentation, hunting, and selective logging modify forests ...in myriad ways and their effects on animal-mediated seed dispersal have been examined in many case studies. However, the overall effects of different types of human disturbance on animal-mediated seed dispersal are still unknown. We identified 35 articles that provided 83 comparisons of animal-mediated seed dispersal between disturbed and undisturbed forests; all comparisons except one were conducted in tropical or subtropical ecosystems. We assessed the effects of forest fragmentation, hunting, and selective logging on seed dispersal of fleshy-fruited tree species. We carried out a meta-analysis to test whether forest fragmentation, hunting, and selective logging affected 3 components of animal-mediated seed dispersal: frugivore visitation rate, number of seeds removed, and distance of seed dispersal. Forest fragmentation, hunting, and selective logging did not affect visitation rate and were marginally associated with a reduction in seed-dispersal distance. Hunting and selective logging, but not fragmentation, were associated with a large reduction in the number of seeds removed. Fewer seeds of large-seeded than of small-seeded tree species were removed in hunted or selectively logged forests. A plausible explanation for the consistently negative effects of hunting and selective logging on large-seeded plant species is that large frugivores, as the predominant seed dispersers for large-seeded plant species, are the first animals to be extirpated from hunted or logged forests. The reduction in forest area after fragmentation appeared to have weaker effects on frugivore communities and animal-mediated seed dispersal than hunting and selective logging. The differential effects of hunting and selective logging on large-and small-seeded tree species underpinned case studies that showed disrupted plant-frugivore interactions could trigger a homogenization of seed traits in tree communities in hunted or logged tropical forests. La dispersión de semillas por animales es importante para sustentar la diversidad biológica en ecosistemas forestales, particularmente en los trópicos. La fragmentación de bosques, la cacería y la tala selectiva modifican los bosques de muchas maneras y sus efectos sobre la dispersión de semillas por animales han sido examinados en muchos estudios de caso. Sin embargo, todavía se desconocen los efectos generales de los diferentes tipos de perturbación humana sobre la dispersión de semillas por animales. Identificamos 35 artículos que proporcionaron 83 comparaciones de dispersión de semillas por animales entre bosques perturbados y no perturbados; todas las comparaciones excepto una fueron en bosques tropicales o subtropicales. Evaluamos los efectos de la fragmentación del bosque, la cacería y la tala selectiva sobre la dispersión de especies de árboles con frutos carnosos. Efectuamos un meta análisis para probar si la fragmentación del bosque, la cacería y la tala selectiva afectaban a tres componentes de la dispersión de semillas por animales: tasa de visitación de frugívoros, números de semillas removidas y distancia de dispersión de semillas. La fragmentación del bosque, la cacería y la tala selectiva no afectaron la tasa de visitación y estuvieron marginalmente asociadas con la disminución de la distancia de dispersión. La cacería y la tala selectiva, pero no la fragmentación, se asociaron con una reducción importante en el número de semillas removidas. Menos semillas de especies de árboles con semillas grandes que de semillas pequeñas fueron removidas en bosques con cacería o tala selectiva. Una explicación plausible de los efectos consistentemente negativos de la cacería y la tala selectiva sobre las especies con semillas grandes es que los frugívoros grandes, como los dispersores predominantes de especies de plantas con semillas grandes, son los primeros animales extirpados de bosques con cacería o tala. La reducción de la superficie de bosque después de la fragmentación pareció tener efectos más débiles sobre las comunidades de frugívoros y la dispersión de semillas por animales que la cacería y la tala selectiva. Los efectos diferenciales de la cacería y la tala selectiva sobre especies de árboles con semillas grandes y pequeñas sustentaron estudios de caso que mostraron que la alteración de interacciones planta-frugívoro podría detonar la homogenización de atributos de las semillas en comunidades de árboles en bosques tropicales con cacería o tala.
The interactions between plants and their animal pollinators and seed dispersers have moulded much of Earth's biodiversity. Recently, it has been shown that these mutually beneficial interactions ...form complex networks with a well-defined architecture that may contribute to biodiversity persistence. Little is known, however, about which ecological and evolutionary processes generate these network patterns. Here we use phylogenetic methods to show that the phylogenetic relationships of species predict the number of interactions they exhibit in more than one-third of the networks, and the identity of the species with which they interact in about half of the networks. As a consequence of the phylogenetic effects on interaction patterns, simulated extinction events tend to trigger coextinction cascades of related species. This results in a non-random pruning of the evolutionary tree and a more pronounced loss of taxonomic diversity than expected in the absence of a phylogenetic signal. Our results emphasize how the simultaneous consideration of phylogenetic information and network architecture can contribute to our understanding of the structure and fate of species-rich communities.
We evaluate whether species interaction frequency can be used as a surrogate for the total effect of a species on another. Because interaction frequency is easier to estimate than per‐interaction ...effect, using interaction frequency as a surrogate of total effect could facilitate the large‐scale analysis of quantitative patterns of species‐rich interaction networks. We show mathematically that the correlation between interaction frequency (I) and total effect (T) becomes more strongly positive the greater the variation of I relative to the variation of per‐interaction effect (P) and the greater the correlation between I and P. A meta‐analysis using data on I, P and T for animal pollinators and seed dispersers visiting plants shows a generally strong, positive relationship between T and I, in spite of no general relationship between P and I. Thus, frequent animal mutualists usually contribute the most to plant reproduction, regardless of their effectiveness on a per‐interaction basis.
Anthropogenic activities, such as grazing by domestic animals, are considered drivers of environmental changes that may influence the structure of interaction networks. The study of individual‐based ...networks allows testing how species‐level interaction patterns emerge from the pooled interaction modes of individuals within populations. Exponential random graph models (ERGMs) examine the global structure of networks by allowing the inclusion of specific node (i.e. interacting partners) properties as explanatory covariates. Here we assessed the structure of individual plant–frugivore interaction networks and the ecological variables that influence the mode of interactions under different land‐use (grazed versus ungrazed protected areas). We quantified the number of visits, the number of fruits removed per visit and the interaction strength of mammal frugivore species at each individual tree. Additionally we quantified ecological variables at the individual, microhabitat, neighborhood and habitat scales that generated interaction network structure under the different land uses. Individual plant–frugivore networks were significantly modular in both land uses but the number of modules was higher in the grazed areas. We found interaction networks for grazed and ungrazed lands were structured by phenotypic traits of individual trees, by the microhabitat beneath the tree canopy and were affected by habitat modifications of anthropogenic origin. The neighborhood surrounding each individual plant influenced plant–frugivore interactions only at the grazed‐land trees. We conclude that anthropogenic land uses influence the topological patterns of plant–frugivore networks and the frugivore visitation to trees through modification of both habitat complexity and the ecological traits underlying interactions between individual plants and frugivore species.
People depend on benefits provided by ecological systems. Understanding how these ecosystem services – and the ecosystem properties underpinning them – respond to drivers of change is therefore an ...urgent priority. We address this challenge through developing a novel risk‐assessment framework that integrates ecological and evolutionary perspectives on functional traits to determine species’ effects on ecosystems and their tolerance of environmental changes. We define Specific Effect Function (SEF) as the per‐gram or per capita capacity of a species to affect an ecosystem property, and Specific Response Function (SRF) as the ability of a species to maintain or enhance its population as the environment changes. Our risk assessment is based on the idea that the security of ecosystem services depends on how effects (SEFs) and tolerances (SRFs) of organisms – which both depend on combinations of functional traits – correlate across species and how they are arranged on the species’ phylogeny. Four extreme situations are theoretically possible, from minimum concern when SEF and SRF are neither correlated nor show a phylogenetic signal, to maximum concern when they are negatively correlated (i.e., the most important species are the least tolerant) and phylogenetically patterned (lacking independent backup). We illustrate the assessment with five case studies, involving both plant and animal examples. However, the extent to which the frequency of the four plausible outcomes, or their intermediates, apply more widely in real‐world ecological systems is an open question that needs empirical evidence, and suggests a research agenda at the interface of evolutionary biology and ecosystem ecology.
We offer a new synthesis integrating in a single, coherent framework the evolution of organismal traits, ecosystem process and services, and their security or vulnerability in the face of specific kinds of environmental change. Our risk assessment integrates ecological and evolutionary perspectives on functional traits to determine species’ effects on ecosystems and their tolerance of different environmental threats. Applying the assessment to five case studies, we show that the security of ecosystem services depends on how effects and tolerances of organisms – which both depend on combinations of functional traits – correlate across species and how they are arranged on the phylogenetic tree. Our framework highlights the importance of phylogenetic redundancy in species’ effects and the risks of strong phylogenetic patterning in species’ tolerances, and suggests a concrete, new research agenda at the interface of evolutionary biology and ecosystem ecology.
Plant–animal mutualistic networks are interaction webs consisting of two sets of entities, plant and animal species, whose evolutionary dynamics are deeply influenced by the outcomes of the ...interactions, yielding a diverse array of coevolutionary processes. These networks are two‐mode networks sharing many common properties with others such as food webs, social, and abiotic networks. Here we describe generalized patterns in the topology of 29 plant–pollinator and 24 plant–frugivore networks in natural communities. Scale‐free properties have been described for a number of biological, social, and abiotic networks; in contrast, most of the plant–animal mutualistic networks (65.6%) show species connectivity distributions (number of links per species) with a power‐law regime but decaying as a marked cut‐off, i.e. truncated power‐law or broad‐scale networks and few (22.2%) show scale‐invariance. We hypothesize that plant–animal mutualistic networks follow a build‐up process similar to complex abiotic nets, based on the preferential attachment of species. However, constraints in the addition of links such as morphological mismatching or phenological uncoupling between mutualistic partners, restrict the number of interactions established, causing deviations from scale‐invariance. This reveals generalized topological patterns characteristic of self‐organized complex systems. Relative to scale‐invariant networks, such constraints may confer higher robustness to the loss of keystone species that are the backbone of these webs.
1. Dispersal ecology is a broad topical discipline that tackles important conceptual and applied issues, such as the study of the ability of plants to transmit their propagules across fragmented and ...managed landscapes. 2. The relevance of dispersal for plant populations is threefold because: (i) dispersal processes scale from genes and individuals that disperse (or produce propagules to be dispersed) to population dynamics and both local and regional distribution patterns; (ii) by dispersing propagules or individuals and the genes they carry, dispersal inherently links demographic and genetic dynamics across the landscape; and (iii) dispersal elicits key ecological and evolutionary processes that sustain biodiversity, such as species assembly in species-rich communities. The steady improvement of tracking devices and molecular tools that trace the movement or infer provenance of organisms and the pressing need to address conservation issues have expanded the disciplinary boundaries of dispersal ecology. 3. The discussion on the main advances on and challenges for dispersal ecology was the main motivation for the organization of a thematic topic session entitled Dispersal processes driving plant movement: challenges for understanding and predicting range shifts in a changing world at the Annual Meeting of the British Ecological Society (2015, Edinburgh). This session brought together researchers with different types of expertise and interests on dispersal processes and their contributions are now included in this special feature together with a few additional articles. 4. Synthesis. Overall, this special feature illustrates that dispersal ecology spans a broad range of research topics by integrating eight contributions that cover key aspects of this discipline: from conceptual and methodological advances to the study of the ecological and evolutionary outcomes.
Assessing the conservation value of restoration plantings is critical to support the global forest landscape restoration movement. We assessed the implications of tree species selection in the ...restoration of Brazil's Atlantic Forest regarding carbon stocking and species conservation. This assessment was based on a comprehensive dataset of seedling acquisition records from 961 restoration projects, more than14 million seedlings, 192 forest remnants, and functional data from 1,223 tree species. We found that animal‐dispersed trees with larger seeds tend to have higher seed prices, yet are underrepresented in the seedlings acquired for restoration plantations. Compared to forest remnants, fruit supply potentially offered by the species acquired for restoration plantings is lower for birds, but higher for bats. Reduced abundance of medium‐ and/or large‐seeded, animal‐dispersed trees lead to declines of 2.8–10.6% in simulated potential carbon stocking. Given the uncertainty in these estimates, policy interventions may be needed to encourage greater representation of large‐seeded, animal‐dispersed tree species in Atlantic Forest restorations. These findings provide critical guidance for recovering tree functional diversity, plant‐frugivore mutualistic interactions, and carbon stocking in multi‐species tropical forest restoration plantings.
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