About this Research Topic
The term generalism, which relates to the diet breadth or habitat of a given species of animal, is most often used in the context of the former. Interestingly, generalism is rare compared to specialism, in which a species has a limited diet range comprising one or few main food sources. Accepting that ecological specialism is the main driving force governing evolutionary change in living organisms, then perhaps it is not surprising that specialism tends to be the predominant ecological scenario, reducing intra- and interspecific competition. However, so-called generalist species do exist in nature, e.g. racoons - hence it is of importance to explore the questions as to why this occurs. In other words, what are the advantages of generalism vs. specialism, especially because generalism is likely to cause populations of a particular species to stop evolving in the longer term?
Examination of this topic is perhaps one of the most important current topics in biology, as the term generalism is still much cited, yet without any real analysis or definition of what is meant. Knowing what the mechanisms are that allow some species to become generalist is critical to our general understanding of ecological and evolutionary processes. This understanding is also important due to the recent widespread application of molecular techniques, especially DNA sequencing, which has allowed refinements in defining population genetic identity. Importantly, these techniques have revealed a plethora of morphologically similar or identical cryptic forms, including in a diverse range of animal taxa.
Hence, what we once thought to be ‘good species’ in terms of population identity (genetic identity is uniform over a geographic range), can no longer be taken for granted. If such cryptic species fill slightly different ecological niches, then de facto, they probably have different diet breadths. Therefore, this uniformity over a geographic range may not be true, and there may be a geographical and/or temporal element to what animals eat and hence the extent of their diet breadth.
The fossil record shows that most animal species were specialist to a greater or lesser extent, as reflected in their surviving anatomical traits, e.g. the jaws of pterosaurs. Perhaps this is not surprising since species, having evolved to fill novel ecological niches or vacant ones (e.g. porpoises vs. ichthyosaurs), are largely constrained by anatomical, chemical/biochemical/physiological, genetic and behavioral constraints. This means that true generalism is unlikely. For example, many herbivores are heavily constrained by toxic plant secondary antifeedants. Therefore, animals are never free agents in terms of what they eat due to prey defences, including behavior, leading to ‘arms races’ between predator (or parasite) and prey. Why then paradox? Because being generalist is going against the normal course of evolution where new species populations originate by becoming specialist. Further, that the plethora of recently discovered cryptic species in many taxa is highly likely to affect the diet specialism and diet breadth of such taxa, surely a prospect worthy of investigation.
Our hope is that this Research Topic on generalism will allow this topic area to be re-appraised in the light of the new data prevailing, more especially molecular data in relation to the widespread discovery of cryptic forms. We hope and trust that this Research Topic will prove a valuable forum for extending the debate concerning the reality and importance of generalism in nature as this concerns primarily dietary breadth and affects the animal kingdom. We believe that the concept of generalism is a flawed one for the reasons we have outlined above and will expand upon in our contributory Editorial paper on this Research Topic. Having said that, we keep an open mind, and will be accepting of evidence that supports the case for generalism, despite our misgivings. Ultimately, the truth will out, but it will surely be a better truth for having been aired in the forum of public debate and critical appraisal.
Examination of this topic is perhaps one of the most important current topics in biology, as the term generalism is still much cited, yet without any real analysis or definition of what is meant. Knowing what the mechanisms are that allow some species to become generalist is critical to our general understanding of ecological and evolutionary processes. This understanding is also important due to the recent widespread application of molecular techniques, especially DNA sequencing, which has allowed refinements in defining population genetic identity. Importantly, these techniques have revealed a plethora of morphologically similar or identical cryptic forms, including in a diverse range of animal taxa.
Hence, what we once thought to be ‘good species’ in terms of population identity (genetic identity is uniform over a geographic range), can no longer be taken for granted. If such cryptic species fill slightly different ecological niches, then de facto, they probably have different diet breadths. Therefore, this uniformity over a geographic range may not be true, and there may be a geographical and/or temporal element to what animals eat and hence the extent of their diet breadth.
The fossil record shows that most animal species were specialist to a greater or lesser extent, as reflected in their surviving anatomical traits, e.g. the jaws of pterosaurs. Perhaps this is not surprising since species, having evolved to fill novel ecological niches or vacant ones (e.g. porpoises vs. ichthyosaurs), are largely constrained by anatomical, chemical/biochemical/physiological, genetic and behavioral constraints. This means that true generalism is unlikely. For example, many herbivores are heavily constrained by toxic plant secondary antifeedants. Therefore, animals are never free agents in terms of what they eat due to prey defences, including behavior, leading to ‘arms races’ between predator (or parasite) and prey. Why then paradox? Because being generalist is going against the normal course of evolution where new species populations originate by becoming specialist. Further, that the plethora of recently discovered cryptic species in many taxa is highly likely to affect the diet specialism and diet breadth of such taxa, surely a prospect worthy of investigation.
Our hope is that this Research Topic on generalism will allow this topic area to be re-appraised in the light of the new data prevailing, more especially molecular data in relation to the widespread discovery of cryptic forms. We hope and trust that this Research Topic will prove a valuable forum for extending the debate concerning the reality and importance of generalism in nature as this concerns primarily dietary breadth and affects the animal kingdom. We believe that the concept of generalism is a flawed one for the reasons we have outlined above and will expand upon in our contributory Editorial paper on this Research Topic. Having said that, we keep an open mind, and will be accepting of evidence that supports the case for generalism, despite our misgivings. Ultimately, the truth will out, but it will surely be a better truth for having been aired in the forum of public debate and critical appraisal.
Keywords: Adaptation, cryptic species, ecology, evolution, generalism, molecular markers, specialism
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