Insect seed-predator networks respond positively to restoration on a tropical island
Data files
Aug 30, 2024 version files 327.49 KB
Abstract
When non-native species invade ecosystems, coevolved plant-animal interactions and associated ecological functions are altered, often to the detriment of local biodiversity. While mutualistic interactions can benefit from —and assist with— ecological restoration through the removal of non-native species, community-level changes in antagonistic interactions due to restoration are less well understood. Insect seed predators provide important ecosystem functions, but can also have antagonistic effects through pre-dispersal seed predation which can cause fruit abortion or premature fruit drop, potentially affecting plant community composition.
Here, we used a network approach and data on trophic interactions from a large-scale field experiment to investigate the differences in insect seed predator communities between native restored sites (where non-native plants were removed) and unrestored sites dominated by non-native plants on the island of Mahé, Seychelles.
Restored sites contained more individuals and species of seed predators (up by 81% and 50% respectively), and experienced a greater predation intensity (1.06 ± 0.53 vs. 0.27 ± 0.09), and predator specialisation compared to unrestored sites. The proportion of predated samples was similar between treatments (~14%). Beta diversity, measured as species and interaction turnover, increased at restored sites.
Synthesis and applications: Our findings imply that vegetation restoration generates marked biodiversity benefits on native seed predator communities and their interactions. However, removing non-native plants did not result in the elimination of non-native seed predators, which might require targeted control measures. Our results highlight the importance of considering the effects of restoration on antagonistic interactions, in addition to those reported for pollination and seed dispersal services. Management practices should aim to control plant invasions for the conservation of native plant communities that serve as resources and refugia both for mutualists (e.g. seed dispersers, pollinators) and native insect seed-predator antagonists, both of which benefit native ecosystem function.
README: Insect seed-predator networks respond positively to restoration on a tropical island
https://doi.org/10.5061/dryad.ht76hdrr4
Description of the data and file structure
README
Title: Insect seed-predator networks respond positively to restoration on a tropical island
Authors: Alba Costa, Ruben Heleno, Yanick Dufrene, Eleanor Huckle, Sara Beatriz Mendes, Andrew E. Whittington, Frank J.F. van Veen, Christopher N. Kaiser-Bunbury
Journal: Journal of Applied Ecology
Contact Author: Alba Costa; Email: ac920@exeter.ac.uk; a.costa@csic.es
DATASETS
fruit_abundance.csv
Data on fruit abundance of ripe fleshy-fruited plant species collected monthly along linear transects for 12 consecutive months, from September 2018 to August 2019, on the island of Mahé, Seychelles.
Variables:
· date: date of record
· **julian & z_julian: **julian day and scaled julian day, respectively
· site: identity code of each site (“ber”: Bernica, “cas”: Casse Dent, “cop”: Copolia, “res”: La Reserve, “ros”: Rosebelle, “sal”: Salazie, “tea”: Tea Plantation, “tro”: Trois Frères)
· treatment: restoration status (“restored”: sites cleared of all exotic plants between 2011 and 2012; “unrestored”: sites not cleared of exotic plants)
· transect: transect identity
· section: identity of 25-meter section within the transect
· plant_spp: plant species
· plant_origin: origin of the plant species (“native”, “exotic”). In publication, “exotic” = “non-native”
· fruit_crop: total number of fruits recorded
· plant_individuals: number of plant individuals of each species recorded
· fpc: fruits per cápita or fruit_crop/plant_individuals
SP_richness.csv
Species richness of pre-dispersal insect seed predator reared from fruits collected for 12 consecutive months, from September 2018 to August 2019, on the island of Mahé, Seychelles.
Variables:
· treatment: restoration status (“restored”: sites cleared of all exotic plants between 2011 and 2012; “unrestored”: sites not cleared of exotic plants)
· site: identity code of each site (“ber”: Bernica, “cas”: Casse Dent, “cop”: Copolia, “res”: La Reserve, “ros”: Rosebelle, “sal”: Salazie, “tea”: Tea Plantation, “tro”: Trois Frères)
· plant_spp: plant species
· **n: **number of seed predator species
SP_abundance.csv
Species richness of pre-dispersal insect seed predator reared from fruits collected for 12 consecutive months, from September 2018 to August 2019, on the island of Mahé, Seychelles.
Variables:
· treatment: restoration status (“restored”: sites cleared of all exotic plants between 2011 and 2012; “unrestored”: sites not cleared of exotic plants)
· site: identity code of each site (“ber”: Bernica, “cas”: Casse Dent, “cop”: Copolia, “res”: La Reserve, “ros”: Rosebelle, “sal”: Salazie, “tea”: Tea Plantation, “tro”: Trois Frères)
· plant_spp: plant species
· **species: **seed predator species or morphospecies
· **origin: **seed predator biogeographical origin
· **number: **number of seed predator individuals
SP_attack_rates.csv
Proportion of fruit samples (10 fruits) predated by pre-dispersal seed predators. Samples were collected from September 2018 to August 2019, on the island of Mahé, Seychelles.
Variables:
· site: identity code of each site (“ber”: Bernica, “cas”: Casse Dent, “cop”: Copolia, “res”: La Reserve, “ros”: Rosebelle, “sal”: Salazie, “tea”: Tea Plantation, “tro”: Trois Frères)
· month: month of data collection
· treatment: restoration status (“restored”: sites cleared of all exotic plants between 2011 and 2012; “unrestored”: sites not cleared of exotic plants)
· plant_spp: plant species
· plant_origin: origin of the plant species (“native”, “exotic”). In publication, “exotic” = “non-native”
· sample_code: identity of sample containing 10 fruits
· predation: predated sample = 1, non-predated sample = 0
· no_insects: number of seed-predator insect individuals found in sample
· fruit_crop: total number of fruits recorded
predation_intensity.csv
Predation intensity data, measured as mean abundance of seed predators per fruit. Samples were collected from September 2018 to August 2019, on the island of Mahé, Seychelles.
Variables:
· site: identity code of each site (“ber”: Bernica, “cas”: Casse Dent, “cop”: Copolia, “res”: La Reserve, “ros”: Rosebelle, “sal”: Salazie, “tea”: Tea Plantation, “tro”: Trois Frères)
· treatment: restoration status (“restored”: sites cleared of all exotic plants between 2011 and 2012; “unrestored”: sites not cleared of exotic plants)
· plant_spp: plant species
· plant_origin: origin of the plant species (“native”, “exotic”). In publication, “exotic” = “non-native”
· sample_code: identity of sample containing 10 fruits
· insect_abun: number of insects per sample of 10 fruits
· fruits_col: number of fruits per sample
· insect_abun_fruit: number of seed-predator insect individuals per fruit
· fruit_crop: total number of fruits recorded
SP_plant_interactions.csv
Data on the frequency of interactions in matrix format between plants (rows) and pre-dispersal seed predator insects (columns) obtained from fruit samples (10 fruits) collected on eight inselberg plant communities (4 restored and 4 unrestored) on the island of Mahé, Seychelles, over one year (Sep. 2018 to Aug. 2019). Each matrix cell depicts the number of individuals of a seed predator insect found in the samples of a given plant species. The sheet “SP_pooled_freq” contains the data for all sites, “SP_restored_freq” only the interaction data for the four restored sites, and “SP_unrestored_freq” for the unrestored sites.
Code/software
All analyses were conducted in R 4.3.2 (R Core Team, 2022). Poisson generalized mixed effects models (GLMMs) were fitted using the package “lme4” (Bates et al., 2015), negative binomial and truncated poisson models using “glmmTMB” (Brooks et al., 2017), and LMMs using the ‘lmertest’ package (Kuznetsova et al., 2017). Model design and selection followed the recommendations by Zuur et al. (2009) and Harrison et al. (2018).
Methods
The study was carried out on eight inselbergs (steep-sided granitic rock outcrops) of ca. 1 ha on Mahé, the largest granitic island of the Seychelles archipelago, Indian Ocean (- 4.6953°, 55.4999°, 154 km2, 900 m a.s.l.). To restore inselberg communities, all non-native woody plants were removed from four of the inselbergs between 2011 and 2012 by cutting individual plants and applying herbicide to cut stumps (Kaiser-Bunbury et al., 2015), with follow-up control thereafter. The other four inselbergs remained unchanged with both native and non-native species (Kaiser-Bunbury et al., 2017).
To estimate fruit availability at each site, we recorded monthly fruit abundance by counting all ripe fruits of woody fleshy-fruited plant species that are mainly dispersed by endozoochory along fixed linear transects.
To collect seed predators, we sampled fleshy fruits monthly at the eight study sites over one year (Sep. 2018 to Aug. 2019). Samples of ten fruits were collected opportunistically from all individuals of fleshy-fruited species with >10 fruits at each site.
For further information, please see the "Material and methods" section in the associated manuscript