DOI: 10.5061/dryad.7m0cfxpsb
title: Robustness of a meta‐network to alternative habitat loss scenarios

description: Studying how habitat loss affects the tolerance of ecological networks to
 species extinction (i.e. their robustness) is key for our understanding of
 the influence of human activities on natural ecosystems. With networks
 typically occurring as local interaction networks interconnected in space
 (a meta-network), we may ask how the loss of specific habitat fragments
 affects the overall robustness of the meta-network. To address this
 question, for an empirical meta-network of plants, herbivores and natural
 enemies we simulated the removal of habitat fragments in increasing and
 decreasing order of area, age and connectivity for plant extinction and
 the secondary extinction of herbivores, natural enemies and their
 interactions. Meta-network robustness was characterized as the area under
 the curve of remnant species or interactions at the end of a fragment
 removal sequence. To pinpoint the effects of fragment area, age and
 connectivity, respectively, we compared the observed robustness for each
 removal scenario against that of a random sequence. The meta-network was
 more robust to the loss of old (i.e. long-fragmented), large, connected
 fragments than of young (i.e. recently fragmented), small, isolated
 fragments. Thus, young, small, isolated fragments may be particularly
 important to the conservation of species and interactions, while contrary
 to our expectations larger, more connected fragments contribute little to
 meta-network robustness. Our findings highlight the importance of young,
 small, isolated fragments as sources of species and interactions unique to
 the regional level. These effects may largely result from an unpaid
 extinction debt, in which case these fragments are likely to lose species
 over time. Yet, there may also be more long-lasting effects from
 cultivated lands (e.g. water, fertilizers and restricted cattle grazing)
 and network complexity in small, isolated fragments. Such fragments may
 sustain important biological diversity in fragmented landscapes, but
 maintaining their conservation value may depend on adequate restoration
 strategies.
description: To build the meta-network
 we considered all plant-herbivore-natural enemy interactions (as
 presence-absence data) recorded in 14 habitat fragments, which involved
 plant species (herbs and shrubs), endophagous herbivores (gall makers or
 gall inquilines, and leaf miners), ectophagous herbivores (scale insects
 and aphids), and their natural enemies (parasitoids, hyperparasitoids and
 predators). To explore fragment contribution to meta-network robustness,
 we sorted the 14 habitat fragments according to their area, age and six
 connectivity metrics combining geographical distances among fragments,
 neighboring area and similarity in plant resources among fragments. For
 each fragment removal, we considered secondary extinctions of herbivores
 and tertiary extinctions of natural enemies as consequence of the local
 extinction of plant resource, and calculated remnant species richness and
 trophic interactions. We calculated meta-network robustness as the area
 under the curve of remnant species and interactions for a specific removal
 sequence for each trophic guild and interaction type. Finally, we compared
 observed robustness for each removal rule against calculated robustness
 for 100 random fragment removals.