Evolutionary Ecology of Specialisation


The processes that drive the evolution of specialisation are still poorly understood. While theory generally invokes the assumption that generalists bear costs compared to species that have a less intense exploitation of specific resources, the existence of these costs have not received strong empirical support. Recent studies have broadened the dialogue by examining specialisation from a macroevolutionary perspective. Are specialist lineages transitioning towards a broader niche under certain environmental conditions, or are they limited in their evolutionary potential and doomed to eventual extinction? The overall finding is that context dependency is key to driving rapid transitions in niche dimensions and composition. Answers to these questions are fascinating in terms of better understanding the natural world and also have the potential to improve prioritisation of future conservation efforts.

Key Concepts

  • Many ideas about the evolution of specialisation rely on the premise that ‘Jack of all trades is master of none’, that is, generalists are locally outperformed by specialists.
  • Genetic or physiological trade‐offs imply that populations experience reduced performance in one function when selection results in increased performance on another function (antagonistic pleiotropy).
  • The evolution of specialisation depends on how often alternate hosts or environments are encountered, which depends on abundance and range extent of a species and its neighbours.
  • Biogeography, functional trait distributions and range limits create ‘forbidden links’ by precluding pairs of species, or a species and a particular suite of environmental variables, from coexisting.
  • The idea of specialisation applies equally to a species biotic and abiotic niche, yet the expectations for how specialisation may evolve for each aspect of niche may differ.
  • Evolutionary transitions from specialisation to generalisation are common (and vice versa), yet specialists may experience greater extinction rates due to smaller geographical range.
  • The evolutionary ecology of specialisation is emerging as a key component in studies of host–pathogen evolution and conservation biology.

Keywords: interactions; population ecology; ecological networks; community ecology; species interactions; community ecology

Figure 1. Fitness trade‐offs for fungi on A. strigosus versus L. bicolour. Bradyrhizobium cultured from L. bicolour performed better on L. bicolour and vice versa of Bradyrhizobium cultured from A. strigosus. Success of Bradyrhizobium genotypes isolated from conspecific versus allospecific hosts. Closed circles indicate growth of A. strigosus test plants; open circles indicate growth of L. bicolor test plants. Error bars represent ±1 standard error. (Reproduced from Ehlinger et al. (2014) © BioMed Central).
Figure 2. The effects of environmental variance on the evolution of specialisation. Solid bold arrows reflect positive relationships and fine dashed arrows reflect negative relationships (the effects of productivity and complexity of the environment are relatively unknown). All of these factors contribute to manifestation of specialised interactions between organisms (e.g. plant–pollinator interactions whereby both partners harbour a suite of matching traits). The image here depicts a sunbird getting its food from the bottom of an aloe flower, while receiving pollen on its head. It will deliver this pollen to the next visited plant, thus achieving pollination for the aloe plant. The shape of its beak and head allows it to match the flower morphology. The extent to which habitat specialisation of aloes (Aloe sp. are largely restricted to arid environments) increases the predictability of interactions with certain pollinators and fosters the evolution of biotic specialisation requires further study. (Reproduced from Poisot et al. (2011) © The National Center for Biotechnology Information.)
Figure 3. Phylogenetic (a) and geographical (b) specificity patterns. (Reproduced with permission from Barrett LG and Heil M. (2012) © Elsevier).
Figure 4. (a) The versatility of pollinators is often a function of their mouthparts (figure modified from Fontaine et al., ) that either allow or prevent access to the rewards, especially to restrictive flowers. The restrictiveness of flowers is often a trait that exhibits phylogenetic signal in communities (e.g. closely related species will exhibit similarity in floral restrictiveness) and this will translate into certain pollinators exhibiting a higher degree of phylogenetic specificity (b). In (b), plants that have restrictive flowers (e.g. tubular, dark blue circles on the left) restrict visits from pollinators with short tongues (e.g. syrphids; light blue circles on the right). Long‐tongued pollinators (dark blue circles on the right) have fewer forbidden links than short‐tongued pollinators and, thus, unrestrictive flowers (light blue circles on the left may receive visits from a more diverse set of pollinators. (Reproduced from Vamosi JC, Moray CM, Garcha NK, Chamberlain SA, and Mooers AØ. (2014) © John Wiley and Sons Ltd. Published under the terms of the Creative Commons Attribution License.)


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Further Reading

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Vamosi, Jana C, and Poisot, Timothée(Feb 2016) Evolutionary Ecology of Specialisation. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0026281]