Presence Of Mutualists Research Articles

The potential impacts of invasions on native symbionts

Symbionts, including parasites, pathogens, and mutualists, can play important roles in determining whether or not invasions by host species will be successful. Loss of enemies from the native habitat, such as parasites and pathogens, can allow for higher invader fitness in the invaded habitat. The presence of mutualists (e.g., pollinators, seed dispersers, mycorrhizae, and rhizobial bacteria) in the invaded habitat can facilitate invasion success. Although there has been a great deal of research focusing on how invading hosts may benefit from enemy losses or mutualist gains, far less attention has focused on how native symbiont populations and communities respond to invasion by non‐indigenous hosts and symbionts. In this paper, we present a conceptual framework examining how symbionts such as parasites, pathogens, commensals, and mutualists can influence invader success and whether these native symbionts will benefit or decline during invasion. The first major factor in this framework is the competence of the invading host relative to the native hosts. Low‐ or non‐competent hosts that support few if any native symbionts could cause declines in native symbiont taxa. Competent invading hosts could potentially support native parasites, pathogens, commensals, and mutualists, especially if there is a closely related or similar host in the invaded range. These symbionts could inhibit or facilitate invasion or have no discernible effect on the invading host. An understanding of how native symbionts interact with competent versus non‐competent invading hosts as well as various invading symbionts is critical to our understanding of invasion success, its consequences for invaded communities and how native symbionts in these communities will fare in the face of invasion.

Habitat variation, mutualism and predation shape the spatio‐temporal dynamics of tansy aphids

1. Spatially distributed resources can lead to the formation of metapopulations, where individual subpopulations are often small and can experience frequent local extinction events followed by recolonisation. An example of terrestrial metapopulations are specialised phytophagous insects on their patchily distributed host plants.2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small‐scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered.3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within‐field dispersal determined the spatio‐temporal distribution of aphid colonies.4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation.5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio‐temporal dynamics of tansy aphids, particularly in a small‐scale field site.

Resource availability determines stability for mutualist–pathogen–host interactions

Traditional explorations of interspecific interactions have generated extensive bodies of theory on mutualism and disease independently, but few studies have considered the interaction between them. We developed a model exploring the interactions among a fungal mutualist, a viral pathogen, and their shared plant host. Both microbes were assumed to alter the uptake and use of nutrients by the plant. We found that the productivity of the system and the strength of the plant–fungal mutualism influenced community dynamics. In particular, at low productivity, the pathogen may depend on the presence of the fungal mutualist for persistence. Furthermore, under some conditions, both the productivity of the system and the strength of the plant–fungal mutualism may simultaneously cause the mutualist to go extinct. We note the presence of cyclic plant–pathogen population dynamics only in the presence of the mutualist. As found in other models of consumer–resource interactions, cyclic dynamics were driven by high productivity, but, in contrast to simpler systems, high pathogen effectiveness did not consistently lead to cyclic dynamics. In total, association with mutualists can alter host–pathogen interactions, and the reverse is also true in that pathogens may alter host–mutualist interactions.

Mutualism: the most desirable interaction for permanence of multispecies ecological communities

The question of long term survival of species in a model governed by a system of four autonomous differential equations is considered. The criteria used is the ecologically realistic one of permanence that is populations with all initial values positive must remain positive, greater than some fixed positive numbers. We propose and analyse a four species mathematical model in which mutualism occurs with prey. The present work is in continuation of the work of Rai and Singh (J Int Acad Phys Sci 12:151–172, 2008), in which we have discussed stability analysis along with boundedness of solutions of initial value problems. Here we will discuss conditions for permanence of all the species with special reference to reversal of outcome due to presence of mutualist in a competitive ecosystem.

Multiple defender effects: synergistic coral defense by mutualist crustaceans

The majority of our understanding of mutualisms comes from studies of pairwise interactions. However, many hosts support mutualist guilds, and interactions among mutualists make the prediction of aggregate effects difficult. Here, we apply a factorial experiment to interactions of 'guard' crustaceans that defend their coral host from seastar predators. Predation was reduced by the presence of mutualists (15% reduction in predation frequency and 45% in volume of coral consumed). The frequency of attacks with both mutualists was lower than with a single species, but it did not differ significantly from the expected frequency of independent effects. In contrast, the combined defensive efficacy of both mutualist species reduced the volume of coral tissue lost by 73%, significantly more than the 38% reduction expected from independent defensive efforts, suggesting the existence of a cooperative synergy in defensive behaviors of 'guard' crustaceans. These emergent 'multiple defender effects' are statistically and ecologically analogous to the emergent concept of 'multiple predator effects' known from the predation literature.