30,101 research outputs found
Competition and cooperation in one-dimensional stepping stone models
Cooperative mutualism is a major force driving evolution and sustaining
ecosystems. Although the importance of spatial degrees of freedom and number
fluctuations is well-known, their effects on mutualism are not fully
understood. With range expansions of microbes in mind, we show that, even when
mutualism confers a distinct selective advantage, it persists only in
populations with high density and frequent migrations. When these parameters
are reduced, mutualism is generically lost via a directed percolation process,
with a phase diagram strongly influenced by an exceptional DP2 transition.Comment: 8 pages, 4 figure
Global stability of the coexistence equilibrium for a general class of models of facultative mutualism
Many models of mutualism have been proposed and studied individually. In this paper, we develop a general class of models of facultative mutualism that covers many of such published models. Using mild assumptions on the growth and self-limiting functions, we establish necessary and sufficient conditions on the boundedness of model solutions and prove the global stability of a unique coexistence equilibrium whenever it exists. These results allow for a greater flexibility in the way each mutualist species can be modelled and avoid the need to analyse any single model of mutualism in isolation. Our generalization also allows each of the mutualists to be subject to a weak Allee effect. Moreover, we find that if one of the interacting species is subject to a strong Allee effect, then the mutualism can overcome it and cause a unique coexistence equilibrium to be globally stable
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The Central Symbiosis of Molecular Biology: Molecules in Mutualism.
As illustrated by the mitochondrion and the eukaryotic cell, little in biology makes sense except in light of mutualism. Mutualisms are persistent, intimate, and reciprocal exchanges; an organism proficient in obtaining certain benefits confers those on a partner, which reciprocates by conferring different benefits. Mutualisms (i) increase fitness, (ii) inspire robustness, (iii) are resilient and resistant to change, (iv) sponsor co-evolution, (v) foster innovation, and (vi) involve partners that are distantly related with contrasting yet complementary proficiencies. Previous to this work, mutualisms were understood to operate on levels of cells, organisms, ecosystems, and even societies and economies. Here, the concepts of mutualism are extended to molecules and are seen to apply to the relationship between RNA and protein. Polynucleotide and polypeptide are Molecules in Mutualism. RNA synthesizes protein in the ribosome and protein synthesizes RNA in polymerases. RNA and protein are codependent, and trade proficiencies. Protein has proficiency in folding into complex three-dimensional states, contributing enzymes, fibers, adhesives, pumps, pores, switches, and receptors. RNA has proficiency in direct molecular recognition, achieved by complementary base pairing interactions, which allow it to maintain, record, and transduce information. The large phylogenetic distance that characterizes partnerships in organismal mutualism has close analogy with large distance in chemical space between RNA and protein. The RNA backbone is anionic and self-repulsive and cannot form hydrophobic structural cores. The protein backbone is neutral and cohesive and commonly forms hydrophobic cores. Molecules in Mutualism extends beyond RNA and protein. A cell is a consortium of molecules in which nucleic acids, proteins, polysaccharides, phospholipids, and other molecules form a mutualism consortium that drives metabolism and replication. Analogies are found in systems such as stromatolites, which are large consortia of symbiotic organisms. It seems reasonable to suggest that 'polymers in mutualism relationships' is a useful and predictive definition of life
The joint influence of competition and mutualism on the biodiversity of mutualistic ecosystems
Relations among species in ecosystems can be represented by complex networks
where both negative (competition) and positive (mutualism) interactions are
concurrently present. Recently, it has been shown that many ecosystems can be
cast into mutualistic networks, and that nestedness reduces effective
inter-species competition, thus facilitating mutually beneficial interactions
and increasing the number of coexisting species or the biodiversity. However,
current approaches neglect the structure of inter-species competition by
adopting a mean-field perspective that does not deal with competitive
interactions properly. Here, we introduce a framework based on the concept of
multilayer networks, which naturally accounts for both mutualism and
competition. Hence, we abandon the mean field hypothesis and show, through a
dynamical population model and numerical simulations, that there is an
intricate relation between competition and mutualism. Specifically, we show
that when all interactions are taken into account, mutualism does not have the
same consequences on the evolution of specialist and generalist species. This
leads to a non-trivial profile of biodiversity in the parameter space of
competition and mutualism. Our findings emphasize how the simultaneous
consideration of positive and negative interactions can contribute to our
understanding of the delicate trade-offs between topology and biodiversity in
ecosystems and call for a reconsideration of previous findings in theoretical
ecology, as they may affect the structural and dynamical stability of
mutualistic systems.Comment: 11 pages. Submitted for publicatio
Asexual grass endophyte symbiosis - mutual exploitation or reciprocal cooperation?
Asexual endophyte-grass associations are generally viewed as the epitome of specialized mutualism because of reciprocal benefits to the partners
THE ECOLOGY OF MUTUALISM
Elementary ecology texts tell us that organisms interact in three fundamen tal ways, generally given the names competition, predation, and mutualism. The third member has gotten short shrift (264), and even its name is not generally agreed on. Terms that may be considered synonyms, in whole or part, are symbiosis, commensalism, cooperation, protocooperation, mutual aid, facilitation, reciprocal altruism, and entraide. We use the term mutualÂism, defined as an interaction between species that is beneficial to both, since it has both historical priority (311) and general currency. Symbiosis is the living together of two organisms in close association, and modifiers are used to specify dependence on the interaction (facultative or obligate) and the range of species that can take part (oligophilic or polyphilic). We make the normal apologies concerning forcing continuous variation and diverse interactions into simple dichotomous classifications, for these and all subsequent definitions
Mutualism supports biodiversity when the direct competition is weak
A key question of theoretical ecology is which properties of ecosystems favour their stability and help maintaining biodiversity. This qu estion recently reconsid- ered mutualistic systems, generating intense controversy about the role of mutu- alistic interactions and their network architecture. Here we show analytically and verify with simulations that reducing the effective intersp ecific competition and the propagation of perturbations positively influences struct ural stability against envi- ronmental perturbations, enhancing persistence. Notewor thy, mutualism reduces the effective interspecific competition only when the direct interspecific competition is weaker than a critical value. This critical competition i s in almost all cases larger in pollinator networks than in random networks with the same connectance. Highly connected mutualistic networks reduce the propagation of e nvironmental perturba- tions, a mechanism reminiscent of MacArthur’s proposal tha t ecosystem complexity enhances stability. Our analytic framework rationalizes p revious contradictory re- sults, and it gives valuable insight on the complex relation ship between mutualism and biodiversity
Estimating the tolerance of species to the effects of global environmental change
Global environmental change is affecting species distribution and their
interactions with other species. In particular, the main drivers of
environmental change strongly affect the strength of interspecific interactions
with considerable consequences to biodiversity. However, extrapolating the
effects observed on pair-wise interactions to entire ecological networks is
challenging. Here we propose a framework to estimate the tolerance to changes
in the strength of mutualistic interaction that species in mutualistic networks
can sustain before becoming extinct. We identify the scenarios where generalist
species can be the least tolerant. We show that the least tolerant species
across different scenarios do not appear to have uniquely common
characteristics. Species tolerance is extremely sensitive to the direction of
change in the strength of mutualistic interaction, as well as to the observed
mutualistic trade-offs between the number of partners and the strength of the
interactions.Comment: Nature Communications 4, Article number: 2350, (2013
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