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The missing part of seed dispersal networks: structure and robustness of bat-fruit interactions.

Mello MA, Marquitti FM, Guimarães PR, Kalko EK, Jordano P, de Aguiar MA - PLoS ONE (2011)

Bottom Line: Primary frugivores interacted with a larger proportion of the plants available and also occupied more central positions; furthermore, their extinction caused larger changes in network structure.We conclude that bat-fruit networks are highly cohesive and robust mutualistic systems, in which redundancy is high within modules, although modules are complementary to each other.Dietary specialization seems to be an important structuring factor that affects the topology, the guild structure and functional roles in bat-fruit networks.

View Article: PubMed Central - PubMed

Affiliation: Institute of Experimental Ecology, University of Ulm, Ulm, Germany. marmello@gmail.com

ABSTRACT
Mutualistic networks are crucial to the maintenance of ecosystem services. Unfortunately, what we know about seed dispersal networks is based only on bird-fruit interactions. Therefore, we aimed at filling part of this gap by investigating bat-fruit networks. It is known from population studies that: (i) some bat species depend more on fruits than others, and (ii) that some specialized frugivorous bats prefer particular plant genera. We tested whether those preferences affected the structure and robustness of the whole network and the functional roles of species. Nine bat-fruit datasets from the literature were analyzed and all networks showed lower complementary specialization (H(2)' = 0.37±0.10, mean ± SD) and similar nestedness (NODF = 0.56±0.12) than pollination networks. All networks were modular (M = 0.32±0.07), and had on average four cohesive subgroups (modules) of tightly connected bats and plants. The composition of those modules followed the genus-genus associations observed at population level (Artibeus-Ficus, Carollia-Piper, and Sturnira-Solanum), although a few of those plant genera were dispersed also by other bats. Bat-fruit networks showed high robustness to simulated cumulative removals of both bats (R = 0.55±0.10) and plants (R = 0.68±0.09). Primary frugivores interacted with a larger proportion of the plants available and also occupied more central positions; furthermore, their extinction caused larger changes in network structure. We conclude that bat-fruit networks are highly cohesive and robust mutualistic systems, in which redundancy is high within modules, although modules are complementary to each other. Dietary specialization seems to be an important structuring factor that affects the topology, the guild structure and functional roles in bat-fruit networks.

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Differences among species in network properties.Interesting differences were found regarding the functional roles of different species. (a) Bats and plants interacted with a similar proportion of partners in the networks (similar proportion of interactions), whereas (b) bats occupied more central positions (higher betweenness centrality). Bat species considered as primary frugivores (c) interacted with a higher proportion of plants and (d) occupied more central positions than bat species considered as secondary or opportunistic frugivores. The main horizontal line shows the median, boxes represent quartiles, and whiskers depict 95% intervals.
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pone-0017395-g002: Differences among species in network properties.Interesting differences were found regarding the functional roles of different species. (a) Bats and plants interacted with a similar proportion of partners in the networks (similar proportion of interactions), whereas (b) bats occupied more central positions (higher betweenness centrality). Bat species considered as primary frugivores (c) interacted with a higher proportion of plants and (d) occupied more central positions than bat species considered as secondary or opportunistic frugivores. The main horizontal line shows the median, boxes represent quartiles, and whiskers depict 95% intervals.

Mentions: Each species, bat or plant, interacted on average with about one-third of all partners available in each network. The proportion of interactions was similar between bats (kr = 0.29±0.24) and plants (kr = 0.28±0.18) (df = 94, t = 0.29, P = 0.77). Betweenness centrality was highly variable among species in each network. On average bats (bc = 0.10±0.15) had higher values than plants (bc = 0.03±0.05) (df = 94, t = 4.48, P<0.001) (Fig. 2). Primary frugivores showed higher values than secondary and occasional frugivores, both for proportion of interactions (N = 87, df = 2, K = 16.76, P<0.001) and for betweenness centrality (N = 87, df = 2, K = 9.91, P = 0.007) (Fig. 2).


The missing part of seed dispersal networks: structure and robustness of bat-fruit interactions.

Mello MA, Marquitti FM, Guimarães PR, Kalko EK, Jordano P, de Aguiar MA - PLoS ONE (2011)

Differences among species in network properties.Interesting differences were found regarding the functional roles of different species. (a) Bats and plants interacted with a similar proportion of partners in the networks (similar proportion of interactions), whereas (b) bats occupied more central positions (higher betweenness centrality). Bat species considered as primary frugivores (c) interacted with a higher proportion of plants and (d) occupied more central positions than bat species considered as secondary or opportunistic frugivores. The main horizontal line shows the median, boxes represent quartiles, and whiskers depict 95% intervals.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3046224&req=5

pone-0017395-g002: Differences among species in network properties.Interesting differences were found regarding the functional roles of different species. (a) Bats and plants interacted with a similar proportion of partners in the networks (similar proportion of interactions), whereas (b) bats occupied more central positions (higher betweenness centrality). Bat species considered as primary frugivores (c) interacted with a higher proportion of plants and (d) occupied more central positions than bat species considered as secondary or opportunistic frugivores. The main horizontal line shows the median, boxes represent quartiles, and whiskers depict 95% intervals.
Mentions: Each species, bat or plant, interacted on average with about one-third of all partners available in each network. The proportion of interactions was similar between bats (kr = 0.29±0.24) and plants (kr = 0.28±0.18) (df = 94, t = 0.29, P = 0.77). Betweenness centrality was highly variable among species in each network. On average bats (bc = 0.10±0.15) had higher values than plants (bc = 0.03±0.05) (df = 94, t = 4.48, P<0.001) (Fig. 2). Primary frugivores showed higher values than secondary and occasional frugivores, both for proportion of interactions (N = 87, df = 2, K = 16.76, P<0.001) and for betweenness centrality (N = 87, df = 2, K = 9.91, P = 0.007) (Fig. 2).

Bottom Line: Primary frugivores interacted with a larger proportion of the plants available and also occupied more central positions; furthermore, their extinction caused larger changes in network structure.We conclude that bat-fruit networks are highly cohesive and robust mutualistic systems, in which redundancy is high within modules, although modules are complementary to each other.Dietary specialization seems to be an important structuring factor that affects the topology, the guild structure and functional roles in bat-fruit networks.

View Article: PubMed Central - PubMed

Affiliation: Institute of Experimental Ecology, University of Ulm, Ulm, Germany. marmello@gmail.com

ABSTRACT
Mutualistic networks are crucial to the maintenance of ecosystem services. Unfortunately, what we know about seed dispersal networks is based only on bird-fruit interactions. Therefore, we aimed at filling part of this gap by investigating bat-fruit networks. It is known from population studies that: (i) some bat species depend more on fruits than others, and (ii) that some specialized frugivorous bats prefer particular plant genera. We tested whether those preferences affected the structure and robustness of the whole network and the functional roles of species. Nine bat-fruit datasets from the literature were analyzed and all networks showed lower complementary specialization (H(2)' = 0.37±0.10, mean ± SD) and similar nestedness (NODF = 0.56±0.12) than pollination networks. All networks were modular (M = 0.32±0.07), and had on average four cohesive subgroups (modules) of tightly connected bats and plants. The composition of those modules followed the genus-genus associations observed at population level (Artibeus-Ficus, Carollia-Piper, and Sturnira-Solanum), although a few of those plant genera were dispersed also by other bats. Bat-fruit networks showed high robustness to simulated cumulative removals of both bats (R = 0.55±0.10) and plants (R = 0.68±0.09). Primary frugivores interacted with a larger proportion of the plants available and also occupied more central positions; furthermore, their extinction caused larger changes in network structure. We conclude that bat-fruit networks are highly cohesive and robust mutualistic systems, in which redundancy is high within modules, although modules are complementary to each other. Dietary specialization seems to be an important structuring factor that affects the topology, the guild structure and functional roles in bat-fruit networks.

Show MeSH
Related in: MedlinePlus