Sampling completeness in seed dispersal networks: When enough is enough

Costa, José Miguel; Silva, Luís P. da; Ramos, Jaime A.; Heleno, Rúben

doi:10.1016/j.baae.2015.09.008

Cited by 44 publications

(51 citation statements)

References 49 publications

(58 reference statements)

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“…In the elfin forest the abundance of the flowerpiercers facilitating access to hummingbirds would take out several “forbidden links” as limitations, diminishing nestedness. Sampling effort did not likely bias our estimate of nestedness given that WNODF is known to be a robust estimator for nestedness in nectarivore bird-plant networks (Vizentin-Bugoni et al, 2016, but see Costa et al, 2016). …”

Section: Discussionmentioning

confidence: 99%

Species interactions in an Andean bird–flowering plant network: phenology is more important than abundance or morphology

González

Loiselle

2016

PeerJ

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Biological constraints and neutral processes have been proposed to explain the properties of plant–pollinator networks. Using interactions between nectarivorous birds (hummingbirds and flowerpiercers) and flowering plants in high elevation forests (i.e., “elfin” forests) of the Andes, we explore the importance of biological constraints and neutral processes (random interactions) to explain the observed species interactions and network metrics, such as connectance, specialization, nestedness and asymmetry. In cold environments of elfin forests, which are located at the top of the tropical montane forest zone, many plants are adapted for pollination by birds, making this an ideal system to study plant–pollinator networks. To build the network of interactions between birds and plants, we used direct field observations. We measured abundance of birds using mist-nets and flower abundance using transects, and phenology by scoring presence of birds and flowers over time. We compared the length of birds’ bills to flower length to identify “forbidden interactions”—those interactions that could not result in legitimate floral visits based on mis-match in morphology. Diglossa flowerpiercers, which are characterized as “illegitimate” flower visitors, were relatively abundant. We found that the elfin forest network was nested with phenology being the factor that best explained interaction frequencies and nestedness, providing support for biological constraints hypothesis. We did not find morphological constraints to be important in explaining observed interaction frequencies and network metrics. Other network metrics (connectance, evenness and asymmetry), however, were better predicted by abundance (neutral process) models. Flowerpiercers, which cut holes and access flowers at their base and, consequently, facilitate nectar access for other hummingbirds, explain why morphological mis-matches were relatively unimportant in this system. Future work should focus on how changes in abundance and phenology, likely results of climate change and habitat fragmentation, and the role of nectar robbers impact ecological and evolutionary dynamics of plant–pollinator (or flower-visitor) interactions.

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Section: Discussionmentioning

confidence: 99%

Species interactions in an Andean bird–flowering plant network: phenology is more important than abundance or morphology

González

Loiselle

2016

PeerJ

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“…; Costa et al . ; Vizentin‐Bugoni et al . ), which means that as seed dispersers are progressively lost in the simulations, it would be difficult to tell apart which topological consequences are exclusively due to defaunation and which are a mathematical consequence of considering increasingly smaller networks.…”

Section: Methodsmentioning

confidence: 99%

Predicting the consequences of disperser extinction: richness matters the most when abundance is low

et al. 2017

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Summary The ongoing biodiversity crisis entails the concomitant loss of species and the ecological services they provide. Global defaunation, and particularly the loss of frugivores, may negatively affect the seed dispersal of fleshy‐fruited plant species, with predictable stronger impacts in simplified communities such as those on oceanic islands. However, logistical difficulties have hindered the experimental and theoretical need to disentangle the roles of species identity, richness (i.e. number of species) and abundance. Consequently, studies to date have focused exclusively on the loss of species richness leaving us largely ignorant regarding how species identity and abundance affect the loss of ecosystem functions. Here, we applied a network approach to disentangle the effects of disperser abundance, richness and identity on the seed dispersal service provided by frugivores to the Galapagos plant community. We found that both abundance and richness of the dispersers significantly affect the function of seed dispersal and that richness becomes increasingly important as disperser abundance declines. Extinction simulations revealed that the order of species loss has profound implications to the plant community. On the one hand, abundant generalist dispersers like the Galapagos lizards, can mitigate the loss of specialized dispersers. On the other hand, specific threats affecting key dispersers can lead to the rapid collapse of the community‐level dispersal services. Our results suggest that the identity of the disperser species lost can have a large effect on the number of plant species dispersed, and generalist species are essential to the persistence of the community dispersal service. Both abundance and species richness of seed dispersers are key and synergistic drivers of the number of plant species dispersed. Consequently, the coupled negative effect of population declines and species extinctions in frugivore assemblages may lead to an accelerated loss of the seed dispersal function. http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12897/suppinfo is available for this article.

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“…Under‐sampling of interactions is in particular likely to contribute to metric bias because interactions are central to the quantification of most network metrics (Vizentin‐Bugoni et al., ). Many metrics have, however, been found to be robust to incomplete sampling of both species and interactions (Costa, Da Silva, Ramos, & Heleno, ; Falcão et al., ; Martinez et al., ; Rivera‐Hutinel et al., ; Vizentin‐Bugoni et al., ). Nestedness, for example, is considered to be robust because of the asymmetric structure of a nested interaction matrix, in which specialist species interact with generalist species rather than other specialists (Nielsen & Bascompte, ).…”

Section: Introductionmentioning

confidence: 99%

“…Weighted metrics can, however, also be sensitive to under‐sampling (see, e.g., Costa et al. ()) as they rely on accurate sampling of interaction frequencies (Blüthgen, Fründ, Vázquez, & Menzel, ).…”

Section: Introductionmentioning

confidence: 99%

The effect of network size and sampling completeness in depauperate networks

Henriksen

Chapple

Chown

et al. 2018

Journal of Animal Ecology

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The accurate estimation of interaction network structure is essential for understanding network stability and function. A growing number of studies evaluate under‐sampling as the degree of sampling completeness (proportional richness observed). How the relationship between network structural metrics and sampling completeness varies across networks of different sizes remains unclear, but this relationship has implications for the within‐ and between‐system comparability of network structure. Here, we test the combined effects of network size and sampling completeness on the structure of spatially distinct networks (i.e., subwebs) in a host–parasitoid model system to better understand the within‐system variability in metric bias. Richness estimates were used to quantify a gradient of sampling completeness of species and interactions across randomly subsampled subwebs. The combined impacts of network size and sampling completeness on the estimated values of twelve unweighted and weighted network metrics were tested. The robustness of network metrics to under‐sampling was strongly related to network size, and sampling completeness of interactions were generally a better predictor of metric bias than sampling completeness of species. Weighted metrics often performed better than unweighted metrics at low sampling completeness; however, this was mainly evident at large rather than small subweb size. These outcomes highlight the significance of under‐sampling for the comparability of both unweighted and weighted network metrics when networks are small and vary in size. This has implications for within‐system comparability of species‐poor networks and, more generally, reveals problems with under‐sampling ecological networks that may otherwise be difficult to detect in species‐rich networks. To mitigate the impacts of under‐sampling, more careful considerations of system‐specific variation in metric bias are needed.

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Sampling completeness in seed dispersal networks: When enough is enough

Cited by 44 publications

References 49 publications

Species interactions in an Andean bird–flowering plant network: phenology is more important than abundance or morphology

Species interactions in an Andean bird–flowering plant network: phenology is more important than abundance or morphology

Predicting the consequences of disperser extinction: richness matters the most when abundance is low

The effect of network size and sampling completeness in depauperate networks

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