The Role of Asymmetric Interactions on the Effect of Habitat Destruction in Mutualistic Networks

Abstract

Plant-pollinator mutualistic networks are asymmetric in their interactions: specialist plants are pollinated by generalist animals, while generalist plants are pollinated by a broad range involving specialists and generalists. It has been suggested that this asymmetric –or disassortative– assemblage could play an important role in determining the observed equal susceptibility of specialist and generalist plants under habitat destruction. At the core of the analysis of the phenomenon lies the observation that specialist plants, otherwise candidates to extinction, could cope with the disruption thanks to their interaction with a few generalist pollinators. We present a theoretical framework that supports this thesis. We analyze a dynamical model of a system of mutualistic plants and pollinators, subject to the destruction of their habitat. We analyze and compare two families of interaction topologies, ranging from highly assortative to highly disassortative ones, as well as real pollination networks. We found that several features observed in natural systems are predicted by the mathematical model. First, there is a tendency to increase the asymmetry of the network as a result of the extinctions. Second, an entropy measure of the differential susceptibility to extinction of specialist and generalist species show that they tend to balance when the network is disassortative. Finally, the disappearance of links in the network, as a result of extinctions, shows that specialist plants preserve more connections than the corresponding plants in an assortative system, enabling them to resist the disruption.

Mycorrhiza Networks Promote Biodiversity and Stabilize the Tropical Mountain Rain Forest Ecosystem: Perspectives for Understanding Complex Communities

“…Numerical simulations revealed that the nested pattern with many weak, asymmetric dependences was crucial for stabilizing complex mutualistic networks (Thébault and Fontaine 2010 and literature therein), made the communities more robust to random extinctions or loss of keystone species (Memmot et al 2004;Burgos et al 2007;Mello et al 2011) and to habitat destruction (Fortuna and Bascompte 2006;Abramson et al 2011). Higher species richness, symmetric interaction strength and increased nestedness improved stability of mutually interacting assemblages when simultaneously considered in simulations based on non-linear functional responses (Okuyama and Holland 2008).…”

Respiratory distress and chest pain: a perforated peptic ulcer with an unusual presentation

“…Small studies have examined this and suggested that CT is 100% sensitive in the diagnosis of pneumoperitoneum, whereas upright chest film was only 33% sensitive for small pockets of air [15]. No studies have compared contrast versus non-contrast CT for this disease, but both are capable of making an accurate diagnosis [10,11,16]. In a small minority of patients with perforated duodenal ulcers, there will be no free air, and only free fluid will be present on CT [16].…”

Predicting the effect of competition on secondary plant extinctions in plant–pollinator networks

“…In these systems, however, competitive interactions, both among plants and among pollinators, are also likely. Despite this, competition is ignored in all topological/static models (Memmott et al 2004, Kaiser‐Bunbury et al 2010) and most dynamic models (Bascompte et al 2006, Fortuna and Bascompte 2006, Abramson et al 2011) of plant– pollinator networks. We hypothesize that the inclusion of interspecific competition in plant–pollinator mutualism networks will alter predictions regarding system‐level properties.…”

“…To answer these questions, we modify the plant–pollinator network model from Abramson et al (2011) to account for plant competition. The resulting model assumes plant–pollinator dynamics on time‐scales over which community dynamics can be expected to equilibrate following pollinator losses, and thus accounts for the long‐term effects of interplay between the pollinator and plant communities.…”