Dispersal Networks Research Articles

Are fragments fruitful? A comparison of plant–seed disperser communities between fragments and contiguous forest in north‐east India

AbstractPlant–seed disperser interactions are critical for maintaining tropical plant diversity. However, these interactions are altered by habitat fragmentation, a pervasive threat to the tropics globally. We compared vegetation structure, richness and composition of plant–avian seed disperser interactions across two forest fragments (area: ~25 km2), and one contiguous forest site in the last remaining lowland tropical forests in north‐east India. We used network‐level indices (nestedness, generality, and vulnerability) and species‐level indices (degree and species strength) to identify key plant and bird groups across the three sites. We found that the three sites varied in habitat structure and were more similar in the composition of avian seed dispersers than plants. The low similarity in plant‐seed disperser interactions between the three sites was likely influenced by low similarity in fruiting plants. The fragmented sites exhibited fewer pairwise interactions and were characterized by a higher representation of small‐seeded plants, climbers, and open‐forest birds. Small‐bodied birds (bulbuls and barbets) played a central role in all the seed dispersal networks, while large‐bodied birds (hornbills) performed persistent interactions with large‐seeded plants at all sites. This is one of the first studies from the Asian tropics to investigate the differences in the plant–avian seed disperser communities between forest fragments and contiguous forest. Our findings highlight the conservation value of fragments given their potential to hold a distinct set of plant–seed disperser interactions, thereby maintaining functional diversity in fragmented tropical landscapes.Abstract in Hindi is available with online material.

Forest cover and connectivity have pervasive effects on the maintenance of evolutionary distinct interactions in seed dispersal networks

Seed dispersal by animals is one of the most important ecological processes in tropical forests, entailing millions of years of evolutionary adaptations of plants and frugivorous animals forming networks of interactions that, ultimately, contribute to the resilience of such forests. We analyze 29 seed dispersal networks in the threatened Atlantic Forest biodiversity hotspot, with data on the frequency of feeding visits by birds to fruiting plants to answer: 1) which are the effects of forest cover and landscape connectivity on the maintenance of phylogenetic diversity (PD) of interacting birds and plants and the evolutionary distinctiveness of the interactions (EDi) between them; and 2) how EDi and plant/bird PD affects the robustness of the interaction networks? We found that forest cover positively influences both plant and bird PD and EDi. Landscape connectivity is an important predictor of bird PD, but not plant PD, suggesting that the spatial arrangement of forest remnants is essential for guaranteeing bird movement among forest fragments. Furthermore, interaction networks of areas with higher PD and EDi had great robustness to the simulated extinction of species, which underscore the importance of larger forest blocks for conserving evolutionary information and, consequently, the health and natural resistance of seed dispersal networks against environmental change.

Host specificity and interaction networks of insects feeding on seeds and fruits in tropical rainforests

In the tropics, antagonistic seed predation networks may have different properties than mutualistic pollination and seed dispersal networks, but the former have been considerably less studied. We tested whether the structure of antagonistic tripartite networks composed of host plants, insects developing within seeds and fruits, and their insect parasitoids could be predicted from plant phylogenetic distance and plant traits. We considered subsets of the networks (‘subnetworks') at three rainforest locations (Panama, Thailand, Papua New Guinea), based on insect families, plant families or plant functional groups. We recorded 3197 interactions and observed a low percentage of realized interactions, especially in Panama, where insect host specificity was higher than in Thailand or New Guinea. Several factors may explain this, including insect faunal composition, incidence of dry fruits, high fruit production and high occurrence of Fabaceae at the Panamanian site. Host specificity was greater among seed‐eaters than pulp‐eaters and for insects feeding on dry fruits as opposed to insects feeding on fleshy fruits. Plant species richness within plant families did not influence insect host specificity, but site characteristics may be important in this regard. Most subnetworks were extremely specialized, such as those including Tortricidae and Bruchinae in Panama. Plant phylogenetic distance, plant basal area and plant traits (fruit length, number of seeds per fruit) had important effects on several network statistics in regressions weighted by sampling effort. A path analysis revealed a weak direct influence of plant phylogenetic distance on parasitoid richness, indicating limited support for the ‘nasty host hypothesis'. Our study emphasizes the duality between seed dispersal and seed predation networks in the tropics, as key plant species differ and host specificity tends to be low in the former and higher in the latter. This underlines the need to study both types of networks for sound practices of forest regeneration and conservation.

Animal‐mediated seed dispersal in India: Implications for conservation of India’s biodiversity

AbstractEffective seed dispersal is critical for forest regeneration and recruitment as well as the restoration of degraded lands. Most tropical tree species depend on frugivorous animals to disperse their seeds; frugivore‐mediated seed dispersal is thus crucial for biodiversity conservation in megadiverse tropical systems such as India. The fauna in India are increasingly threatened due to anthropogenic interventions such as deforestation and hunting. Thus, it is imperative to have an understanding of plant–frugivore interactions across the country to curb further biodiversity loss by ensuring the maintenance of these ecological processes. In this paper, I reviewed the literature on seed dispersal by animals in India to identify important groups that disperse many plant species and/or are the only recorded dispersers of certain plant species. Hornbills, bulbuls, bears, cattle, deer, civets, elephants, macaques, nilgais, Old World fruit bats, and wild pigs meet these criteria; overall 18 species were included in this list. Six of these species are currently “Threatened” on the IUCN Red List and their loss can lead to limited dispersal for at least 86 plant species. I suggest ensuring the protection of the important seed dispersers identified in this paper, irrespective of their conservation status, to prevent further biodiversity loss. The review reveals that plant–animal interactions in India are understudied and a major knowledge gap exists with regard to seed dispersal networks within the country.

Changes in the structure of seed dispersal networks when including interaction outcomes from both plant and animal perspectives

Interaction frequency is the most common currency in quantitative ecological networks, although interaction quality can also affect benefits provided by mutualisms. Here, we evaluate if interaction quality can modify network topology, species' role and whether such changes affect community vulnerability to species loss. We use a well‐examined study system (bird–lizard and fleshy‐fruited plants in the ‘thermophilous' woodland of the Canary Islands) to compare network and species‐level metrics from a network based on fruit consumption rates (interaction frequency, IF), against networks reflecting functional outcomes: a seed dispersal effectiveness network (SDE) quantifying recruitment, and a fruit resource provisioning network (FRP), accounting for the nutrient supply of fruits. Nestedness decreased in the FRP and the SDE networks, due to the lack of association between fruit consumption rates and 1) nutrient content and; 2) recruitment at the seed deposition sites, respectively. The FRP network showed lower niche overlap due to resource use complementarity among frugivores. Interaction evenness was lower in the SDE network, in response to a higher dominance of lizards in the recruitment of heliophilous species. Such changes, however, did not result in enhanced vulnerability against extinctions. At the plant species level, strength changed in the FRP network in frequently consumed or highly nutritious species. The number of effective partners decreased for species whose seeds were deposited in unsuitable places for recruitment. In frugivores, strength was consistent across networks (SDE vs IF), showing that consumption rates outweighed differences in dispersal quality. In the case of lizards, the increased importance of nutrient‐rich species resulted in a higher number of effective partners.Our work shows that although frequency strongly impacts interaction effects, accounting for quality improves our inferences about interaction assembly and species role. Thus, future studies including interaction outcomes from both partners' perspectives will provide valuable insights about the net effects of mutualistic interactions.

Observing frugivores or collecting scats: a method comparison to construct quantitative seed dispersal networks

Mutualistic interactions form the basis for many ecological processes and are often analyzed within the framework of ecological networks. These interactions can be sampled with a range of methods and first analyses of pollination networks sampled with different methods showed differences in common network metrics. However, it is yet unknown if metrics of seed dispersal networks are similarly affected by the sampling method and if different methods detect a complementary set of frugivores. This is necessary to better understand the (dis‐)advantages of each method and to identify the role of each frugivore for the seed dispersal process.Here, we compare seed removal networks based on the observation of 2189 frugivore visits on ten focal plant species with seed deposition networks constructed by DNA barcoding of plant seeds in 3094 frugivore scats. We were interested in whether both methods identify the same disperser species and if species‐level network metrics of plant species were correlated between network types.Both methods identified the same avian super‐generalist frugivores, which accounted for the highest number of dispersed seeds. However, only with DNA barcoding, we detected elusive but frequent mammalian seed dispersers. The overall networks created by both methods were congruent but the plant species' degree, their interaction frequency and their specialization index (d′) differed.Our study suggests that DNA barcoding of defecated and regurgitated seeds can be used to construct quantitative seed deposition networks similar to those constructed by focal observations. To improve the overall completeness of seed dispersal networks it might be useful to combine both methods to detect interactions by both birds and mammals. Most importantly, the DNA barcoding method provides information on the post‐dispersal stage and thus on the qualitative contribution of each frugivore for the plant community thereby linking species interactions to regeneration dynamics of fleshy‐fruited plant species.

Macroevolutionary stability predicts interaction patterns of species in seed dispersal networks.

Assessing deep-time mechanisms affecting the assembly of ecological networks is key to understanding biodiversity changes on broader time scales. We combined analyses of diversification rates with interaction network descriptors from 468 bird species belonging to 29 seed dispersal networks to show that bird species that contribute most to the network structure of plant-frugivore interactions belong to lineages that show higher macroevolutionary stability. This association is stronger in warmer, wetter, less seasonal environments. We infer that the macroevolutionary sorting mechanism acts through the regional pool of species by sorting species on the basis of the available relative differences in diversification rates, rather than absolute rates. Our results illustrate how the interplay between interaction patterns and diversification dynamics may shape the organization and long-term dynamics of ecological networks.

Analysing landscape effects on dispersal networks and gene flow with genetic graphs.

Graph-theoretic approaches have relevant applications in landscape genetic analyses. When species form populations in discrete habitat patches, genetic graphs can be used (a) to identify direct dispersal paths followed by propagules or (b) to quantify landscape effects on multi-generational gene flow. However, the influence of their construction parameters remains to be explored. Using a simulation approach, we constructed genetic graphs using several pruning methods (geographical distance thresholds, topological constraints, statistical inference) and genetic distances to weight graph links (FST , DPS , Euclidean genetic distances). We then compared the capacity of these different graphs to (a) identify the precise topology of the dispersal network and (b) to infer landscape resistance to gene flow from the relationship between cost-distances and genetic distances. Although not always clear-cut, our results showed that methods based on geographical distance thresholds seem to better identify dispersal networks in most cases. More interestingly, our study demonstrates that a sub-selection of pairwise distances through graph pruning (thereby reducing the number of data points) can counter-intuitively lead to improved inferences of landscape effects on dispersal. Finally, we showed that genetic distances such as the DPS or Euclidean genetic distances should be preferred over the FST for landscape effect inference as they respond faster to landscape changes.

Sedimentary microeukaryotes reveal more dispersal limitation and form networks with less connectivity than planktonic microeukaryotes in a highly regulated river

Abstract Microeukaryotes are considered critical for biogeochemical cycles and material transformation in river ecosystems, but their biogeography and underlying mechanisms of their assemblages remain poorly understood. We collected 35 water samples and 26 sediment samples covering an 1,148 km reach of the Lancang River, a highly regulated large river in south‐western China. The planktonic and sedimentary microeukaryotic communities were analysed by sequencing the V4 region of eukaryotic 18S rRNA gene. Factors associated with patterns in microeukaryotic communities were assessed by canonical correlation analysis and neutral models. Species interactions and keystone species in microeukaryotic communities were investigated by co‐occurrence network analysis. The results showed that community composition was distinct between planktonic and sedimentary microeukaryotes, as well as between upstream natural sites and regulated sites downstream. Similar environmental (pH, nutrient concentrations) and spatial (altitude, distance) variables were associated with patterns in community composition of planktonic and sedimentary microeukaryote communities, except that turbidity and water temperature were associated only with patterns in planktonic communities. Neutral models were an excellent fit to the distributions of both planktonic (r2 = 0.67) and sedimentary (r2 = 0.50) microeukaryotic communities. The estimated immigration rate (m) from planktonic communities (m = 0.032) was higher than from sedimentary communities (m = 0.022). Co‐occurrence pattern analysis showed that planktonic microeukaryotic networks had more connectivity but a lower proportion of positive interactions than sedimentary microeukaryotic networks. Keystone species, in particular those belonging to phylum Ascomycota, played essential roles in maintaining stability of both planktonic and sedimentary microeukaryotic communities. Our results showed that the composition of planktonic and sedimentary microeukaryote communities differ, and that diversity in both communities was influenced by river regulation. Given the important roles played by microeukaryotes in nutrient cycling and food webs, such impacts may alter other ecosystem processes in rivers.

Dynamic spatio-temporal patterns of metapopulation occupancy in patchy habitats.

Spatio-temporal dynamics in habitat suitability and connectivity among mosaics of heterogeneous wetlands are critical for biological diversity and species persistence in aquatic patchy landscapes. Despite the recognized importance of stochastic hydroclimatic forcing in driving wetlandscape hydrological dynamics, linking such effects to emergent dynamics of metapopulation poses significant challenges. To fill this gap, we propose here a dynamic stochastic patch occupancy model (SPOM), which links parsimonious hydrological and ecological models to simulate spatio-temporal patterns in species occupancy in wetlandscapes. Our work aims to place ecological studies of patchy habitats into a proper hydrologic and climatic framework to improve the knowledge about metapopulation shifts in response to climate-driven changes in wetlandscapes. We applied the dynamic version of the SPOM (D-SPOM) framework in two wetlandscapes in the US with contrasting landscape and climate properties. Our results illustrate that explicit consideration of the temporal dimension proposed in the D-SPOM is important to interpret local- and landscape-scale patterns of habitat suitability and metapopulation occupancy. Our analyses show that spatio-temporal dynamics of patch suitability and accessibility, driven by the stochasticity in hydroclimatic forcing, influence metapopulation occupancy and the topological metrics of the emergent wetlandscape dispersal network. D-SPOM simulations also reveal that the extinction risk in dynamic wetlandscapes is exacerbated by extended dry periods when suitable habitat decreases, hence limiting successful patch colonization and exacerbating metapopulation extinction risks. The proposed framework is not restricted only to wetland studies but could also be applied to examine metapopulation dynamics in other types of patchy habitats subjected to stochastic external disturbances.

Ecological correlates of species’ roles in highly invaded seed dispersal networks

Ecosystems with a mix of native and introduced species are increasing globally as extinction and introduction rates rise, resulting in novel species interactions. While species interactions are highly vulnerable to disturbance, little is known about the roles that introduced species play in novel interaction networks and what processes underlie such roles. Studying one of the most extreme cases of human-modified ecosystems, the island of O'ahu, Hawaii, we show that introduced species there shape the structure of seed dispersal networks to a greater extent than native species. Although both neutral and niche-based processes influenced network structure, niche-based processes played a larger role, despite theory predicting neutral processes to be predominantly important for islands. In fact, ecological correlates of species' roles (morphology, behavior, abundance) were largely similar to those in native-dominated networks. However, the most important ecological correlates varied with spatial scale and trophic level, highlighting the importance of examining these factors separately to unravel processes determining species contributions to network structure. Although introduced species integrate into interaction networks more deeply than previously thought, by examining the mechanistic basis of species' roles we can use traits to identify species that can be removed from (or added to) a system to improve crucial ecosystem functions, such as seed dispersal.

Frugivory Specialization in Birds and Fruit Chemistry Structure Mutualistic Networks across the Neotropics.

AbstractThe interaction between fruit chemistry and the physiological traits of frugivores is expected to shape the structure of mutualistic seed dispersal networks, but it has been understudied compared with the role of morphological trait matching in structuring interaction patterns. For instance, highly frugivorous birds (i.e., birds that have fruits as the main component of their diets), which characteristically have fast gut passage times, are expected to avoid feeding on lipid-rich fruits because of the long gut retention times associated with lipid digestion. Here, we compiled data from 84 studies conducted in the Neotropics that used focal plant methods to record 35,815 feeding visits made by 317 bird species (155 genera in 28 families) to 165 plant species (82 genera in 48 families). We investigated the relationship between the degree of frugivory of birds (i.e., how much of their diet is composed of fruit) at the genus level and their visits to plant genera that vary in fruit lipid content. We used a hierarchical modeling of species communities approach that accounted for the effects of differences in body size, bird and plant phylogeny, and spatial location of study sites. We found that birds with a low degree of frugivory (e.g., predominantly insectivores) tend to have the highest increase in visitation rates as fruits become more lipid rich, while birds that are more frugivorous tend to increase visits at a lower rate or even decrease visitation rates as lipids increase in fruits. This balance between degree of frugivory and visitation rates to lipid-poor and lipid-rich fruits provides a mechanism to explain specialized dispersal systems and the occurrence of certain physiological nutritional filters, ultimately helping us to understand community-wide interaction patterns between birds and plants.

Chimera and cluster collective states in a dispersal ecological network under state-dependent feedback control and complex habitat structure

Pest control based on an economic threshold (ET) can effectively prevent excessive pest control measures such as pesticide abuse and overharvesting. The instinctive dispersal of pest populations in biological network patches for better survival poses challenges for pest management. As long as the pest density is controlled below the economic threshold and no pest outbreak occurs, the aim of pest management can be achieved and it is not necessary to completely remove the pests. This study focuses on the issues of chimera states and cluster solutions in regular bidirectional biological networks with state-dependent impulsive pest management. We consider the influence of two different control modes on the system states, namely global control and local control. Local control is found to be more likely to induce the chimera state. In addition, in the local coupling mode, a higher coupling strength is more likely to generate a coherent state, whereas a lower coupling strength is more likely to generate chimera and incoherent states. Furthermore, the cluster size is inversely related to the coupling strength under local coupling and global control.

Species dispersal along rivers and streams may have variable importance to metapopulation structure

The ability to prioritize habitats that have spatially varied contributions to species persistence can produce synergistic benefits for regional conservation efforts. However, conservation in spatially diverse landscape-networks requires considering dispersal asymmetry in the context of ecological connectivity and metapopulation persistence. By developing an approach based on metapopulation theory, this study prioritized the importance of habitat (as determined by the habitat quality and spatial position in networks) on metapopulation structure in mountainous streams. As a case study, we examined dispersal via overland and instream networks in a riverine mayfly Rhithrogena sp. cf. japonica in a mountain range of Southwest China. Compared to flow velocity, water depth, and instream nutrient-levels, water temperature was a key factor in determining local habitat suitability for R. sp. cf. japonica. Higher water temperature was linked to poor habitat suitability. Instream pathways were the main dispersal corridors compared with overland movement between tributaries for this mayfly. In basins on the east aspect of this mountain range, either monotonically increasing (i.e., never decreasing) or unimodal (i.e., with a single peak) patterns demonstrated the importance of riverine habitats that occur along elevational gradients. However, the importance of habitat appeared to show no definite patterns with elevation on the west aspect. In terms of metapopulation structure, local quality of habitat contributed more to the regional importance of habitat than its spatial position in the networks. The framework presented highlights that the importance of riverine habitats may be quite variable in species having directional dispersal networks across the fluvial landscape in mountainous areas. Results from this framework can serve as the basis to apply a mechanistic understanding to managing and protecting native populations through regional restoration actions.

Four priority areas to advance invasion science in the face of rapid environmental change

Unprecedented rates of introduction and spread of non-native species pose burgeoning challenges to biodiversity, natural resource management, regional economies, and human health. Current biosecurity efforts are failing to keep pace with globalization, revealing critical gaps in our understanding and response to invasions. Here, we identify four priority areas to advance invasion science in the face of rapid global environmental change. First, invasion science should strive to develop a more comprehensive framework for predicting how the behavior, abundance, and interspecific interactions of non-native species vary in relation to conditions in receiving environments and how these factors govern the ecological impacts of invasion. A second priority is to understand the potential synergistic effects of multiple co-occurring stressors— particularly involving climate change—on the establishment and impact of non-native species. Climate adaptation and mitigation strategies will need to consider the possible consequences of promoting non-native species, and appropriate management responses to non-native species will need to be developed. The third priority is to address the taxonomic impediment. The ability to detect and evaluate invasion risks is compromised by a growing deficit in taxonomic expertise, which cannot be adequately compensated by new molecular technologies alone. Management of biosecurity risks will become increasingly challenging unless academia, industry, and governments train and employ new personnel in taxonomy and systematics. Fourth, we recommend that internationally cooperative biosecurity strategies consider the bridgehead effects of global dispersal networks, in which organisms tend to invade new regions from locations where they have already established. Cooperation among countries to eradicate or control species established in bridgehead regions should yield greater benefit than independent attempts by individual countries to exclude these species from arriving and establishing.

Endozoochory of the same community of plants lacking fleshy fruits by storks and gulls

AbstractAimsResearch into the dispersal of plants lacking a fleshy fruit by avian endozoochory remains limited, particularly regarding the different roles of specific vectors in the same habitat.MethodsWe compared plants dispersed by endozoochory between two migratory waterbirds differing in body size: the lesser black‐backed gull Larus fuscus, and the white stork Ciconia ciconia. We collected faeces and pellets from roosting flocks on dykes in rice fields in Doñana, SW Spain, and extracted intact seeds.ResultsWe recovered 424 intact seeds from excreta, representing 21 plant taxa, 11 of which germinated under laboratory conditions. Eight plant species are considered weeds, four of them as alien species, and only two have a fleshy fruit. Seed abundance and species richness per sample did not differ between storks and gulls. Toadrush (Juncus bufonius) was the dominant species, accounting for 49% of seeds recovered. PERMANOVA and mvabund analyses revealed no differences in the proportions of each plant species dispersed by the two vectors, and seasonal variation in abundance was absent. Overall, germinability was 19%, and declined with increasing delay between sample collection and processing. Transects along dykes identified 52 plant taxa, only 18 of which were recorded in excreta.ConclusionsOverlap in the communities of non‐fleshy‐fruited plants dispersed by two unrelated birds of different size suggests that waterbird plant dispersal networks are different from frugivore networks. Unlike for frugivores, decoupling between seed production and ingestion reduces seasonal variation in endozoochory rates. For Juncus bufonius and other plants, these avian vectors provide maximum dispersal distances several orders of magnitude greater than predicted from their dispersal syndromes. Endozoochory by migratory waterbirds has major implications for plant distributions in a rapidly changing world, and more research is required before we can predict which plants disperse regularly via this mechanism.

Incorporating alternative interaction modes, forbidden links and trait‐based mechanisms increases the minimum trait dimensionality of ecological networks

Abstract Individual‐level traits mediate interaction outcomes and community structure. It is important, therefore, to identify the minimum number of traits that characterise ecological networks, that is, their ‘minimum dimensionality’. Existing methods for estimating minimum dimensionality often lack three features associated with increased trait numbers: alternative interaction modes (e.g. feeding strategies such as active vs. sit‐and‐wait feeding), trait‐mediated ‘forbidden links’ and a mechanistic description of interactions. Omitting these features can underestimate the trait numbers involved, and therefore, minimum dimensionality. We develop a ‘minimum mechanistic dimensionality’ measure, accounting for these three features. The only input our method requires is the network of interaction outcomes. We assume how traits are mechanistically involved in alternative interaction modes. These unidentified traits are contrasted using pairwise performance inequalities between interacting species. For example, if a predator feeds upon a prey species via a typical predation mode, in each step of the predation sequence, the predator's performance must be greater than the prey's. We construct a system of inequalities from all observed outcomes, which we attempt to solve with mixed integer linear programming. The number of traits required for a feasible system of inequalities provides our minimum dimensionality estimate. We applied our method to 658 published empirical ecological networks including primary consumption, predator–prey, parasitism, pollination, seed dispersal and animal dominance networks, to compare with minimum dimensionality estimates when the three focal features are missing. Minimum dimensionality was typically higher when including alternative interaction modes (54% of empirical networks), ‘forbidden interactions’ as trait‐mediated interaction outcomes (92%) or a mechanistic perspective (81%), compared to estimates missing these features. Additionally, we tested minimum dimensionality estimates on simulated networks with known dimensionality. Our method typically estimated a higher minimum dimensionality, closer to the actual dimensionality, while avoiding the overestimation associated with a previous method. Our method can reduce the risk of omitting traits involved in different interaction modes, in failure outcomes or mechanistically. More accurate estimates will allow us to parameterise models of theoretical networks with more realistic structure at the interaction outcome level. Thus, we hope our method can improve predictions of community structure and structure‐dependent dynamics.

Seasonal consistency of the assembling rules in a bird-fruiting plant network

There is an ongoing debate on whether species' traits or neutrality generate recurrent patterns of mutualistic networks. Although there have been recent advances on the issue, many studies neglect the seasonal dynamics of these drivers. In this study, we investigated how pervasive are the drivers (i.e. species’ size, phenological overlap and species relative abundance) of the frequency of pairwise interactions and the aggregate metrics of seasonal seed dispersal networks in a semideciduous forest from the savannahs of Southeastern Brazil. We used a likelihood approach and built probability matrices based on different drivers to compare how they fit in the frequency and structure of the seasonal observed networks. We found that in both seasons trait-based processes, especially phenological overlap between species, best predicted the frequency of pairwise interactions. However, species relative abundances performed better than species traits in explaining most of aggregate network metrics in both seasons, except for the interaction evenness. These findings suggest that ecological and evolutionary processes are seasonally pervasive and determine the ability of species to interact with their partners. Besides, the general structure of the seasonal networks is less sensitive to species traits and its drivers remain seasonally constant. We conclude that our ability to understand the complexity of plant-frugivore interactions depends on assessing the contribution of species traits and their relative abundances to the structure of seasonal-detailed networks.

Graph-theoretic method on the periodicity of coupled predator–prey systems with infinite delays on a dispersal network

In this paper, infinite delays and prey dispersal on a network are considered in multi-patch periodic predator–prey systems. Novel graph-theoretic method is adopted to estimate the uniform upper bounds of unknown solutions to operator equation Lu=λNu. The existence criterion of positive periodic solutions to coupled predator–prey systems is obtained by using classic coincidence degree theory, which is closely related to prey dispersal network in a patch environment. Finally, two numerical examples are also shown to illustrate the effectiveness of theoretical results.

Emergent dispersal networks in dynamic wetlandscapes

The connectivity among distributed wetlands is critical for aquatic habitat integrity and to maintain metapopulation biodiversity. Here, we investigated the spatiotemporal fluctuations of wetlandscape connectivity driven by stochastic hydroclimatic forcing, conceptualizing wetlands as dynamic habitat nodes in dispersal networks. We hypothesized that spatiotemporal hydrologic variability influences the heterogeneity in wetland attributes (e.g., size and shape distributions) and wetland spatial organization (e.g., gap distances), in turn altering the variance of the dispersal network topology and the patterns of ecological connectivity. We tested our hypotheses by employing a DEM-based, depth-censoring approach to assess the eco-hydrological dynamics in a synthetically generated landscape and three representative wetlandscapes in the United States. Network topology was examined for two end-member connectivity measures: centroid-to-centroid (C2C), and perimeter-to-perimeter (P2P), representing the full range of within-patch habitat preferences. Exponentially tempered Pareto node-degree distributions well described the observed structural connectivity of both types of networks. High wetland clustering and attribute heterogeneity exacerbated the differences between C2C and P2P networks, with Pareto node-degree distributions emerging only for a limited range of P2P configuration. Wetlandscape network topology and dispersal strategies condition species survival and biodiversity.