Geographic variation in ecology of coral feeding butterflyfishes and resilience to large scale disturbances

Lawton, Rebecca Joy (2011) Geographic variation in ecology of coral feeding butterflyfishes and resilience to large scale disturbances. PhD thesis, James Cook University.

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Ecological specialisation is often correlated with high extinction risk as specialist species are expected to be disproportionately affected by changes in resource availability and disturbance events compared to generalist counterparts. On coral reefs, highly specialised coral-feeding butterflyfish appear to be most vulnerable to the effects of coral loss. Species with large geographic ranges, such as many butterflyfishes, are traditionally thought to have low risk of extinction if disturbances are patchy in time and space. This is because disturbed locations can be recolonised from viable populations elsewhere. However, as the frequency, intensity, magnitude and extent of disturbance events on coral reefs are predicted to increase, many butterflyfishes may be at considerable risk of global extinction in the future. The persistence of these species through future periods of coral loss will be dependent in part upon their ability to use alternative resources if their preferred coral resources are no longer available, the influence of coral resources on local abundance patterns, and the ability of remnant populations to recolonise disturbed habitats. However, all three factors are largely unknown for most butterflyfishes. This thesis examines variation in the ecology of coral-feeding butterflyfishes across five geographic locations and considers the influence of dietary specialisation on the resilience of local versus global populations of butterflyfish to increasing coral loss.

A range of indices can be used to estimate ecological specialisation but their utility to inform vulnerability predictions is largely unknown. To determine the most informative index to use for quantification of dietary specialisation in coral-feeding butterflyfishes, Chapter 2 compared the performance of four different specialisation indices. Feeding observations were conducted for three butterflyfish species at six sites around Lizard Island, Australia. Levels of dietary specialisation were calculated for each species at each site using four specialisation indices. Differences in the relative levels of dietary specialisation estimated for each of the three butterflyfishes by each of the four indices indicated that the choice of specialisation index can impact considerably on estimates of specialisation. The best estimates of specialisation were provided by indices that incorporated a measure of resource availability because they were able to distinguish between species using a few common resources and those using a few rarer resources disproportionately to availability. Resource selection functions were also found to be highly informative for predicting likely responses of specialist versus generalist consumers to changes in resource availability.

Having determined that specialisation indices incorporating resource availability measures were most appropriate to use, Chapter 3 then examined large-scale geographic variation in dietary specialisation for four coral-feeding butterflyfishes. Detailed estimates of dietary composition and specialisation are available for a few coral-feeding butterflyfishes, however, only a small number of studies have compared resource use to resource availability and these studies have been confined to a few isolated locations. Consequently, the degree that particular butterflyfish species are truly specialised or generalised is unknown. Chapter 3 examined whether patterns of resource use varied among five distinct geographic locations, corresponding with changes in resource availability. Despite varying resource availability, the level of dietary specialisation shown by each of the four species of butterflyfishes varied little among geographically separated locations. Chaetodon vagabundus, C. citrinellus and C. lunulatus all had low levels of dietary specialisation and used different resources in each location. In contrast, Chaetodon trifascialis had high levels of dietary specialisation and used the same few resources in each location. These results indicate that highly specialised species such as C. trifascialis will be highly vulnerable to coral loss as they appear to be largely inflexible in their coral diet, and hence, sensitive to changes in the abundance of this resource. Empirical evidence indicates that both niche breadth and resource availability are key drivers of a species' local abundance and distribution patterns. Numerous studies have found strong links between total hard coral cover and the abundance of coral-feeding butterflyfishes; however, the influence of specific dietary resources on the abundance of individual butterflyfish species has not yet been examined. Chapter 4 investigated the influence of dietary specialisation and resource availability on the local abundance patterns of five butterflyfishes, across five geographic locations. Factors influencing local abundance varied between butterflyfishes with specialised and generalised diets. Resource availability had the strongest influence on the abundance of C. trifascialis - the species with the most specialised diet. Local abundance of C. trifascialis was best predicted by availability of the Acropora corals that it preferentially feeds on. In contrast, abundance of generalist butterflyfishes was best predicted by indices of total resource availability. However, overall, resource availability only explained a small proportion of the variation in local abundance for all five species. These findings suggest that despite their relatively specialised diets, resource availability has limited influence on the local abundance of butterflyfishes and only the most specialised species appear to be consistently limited by prey availability.

Over evolutionary timescales, the resilience of butterflyfishes to coral loss will be determined by their level of population connectivity and the recovery potential of declining populations. Recent studies have indicated that specialised species may have lower genetic diversity and population connectivity than generalist counterparts. Chapter 5 examined whether there were differences in population genetic structure between the dietary specialist C. trifascialis and the dietary generalist C. lunulatus from five locations across the Pacific. Mitochondrial DNA sequences and microsatellite loci were used to detect evidence of population declines and estimate levels of gene flow to enable predictions of likely recovery potential following coral loss. Genetic analyses revealed contrasting demographic histories and levels of genetic structure for the two species. Highly significant tests for genetic bottlenecks indicated that C. trifascialis populations have experienced significant declines in abundance over both recent and historical timescales; however, low levels of genetic structuring and high levels of gene flow were detected among locations. In contrast, there was little evidence of genetic bottlenecks and population declines for C. lunulatus, and higher levels of genetic structuring were detected for this species compared to C. trifascialis. The finding of genetic bottlenecks for C. trifascialis indicates that this species experiences periodic population decline; however, the high gene flow detected among locations suggests C. trifascialis populations will be able to recover from local declines through colonisation from healthy source populations

Overall, this study has shown that coral-feeding butterflyfishes with specialised diets are inflexible in their dietary requirements and therefore, highly vulnerable to localised coral loss caused by major disturbances. However, the availability of preferred coral resources had limited influence on geographical variation in the abundance of specialist species, which were generally common on surveyed reefs. These findings indicate that macro-ecological theories predicting that specialist species are locally rare are not universally true and specialist species often have other characteristics which confer high ecological resilience. Supporting this, molecular data indicated that specialist butterflyfishes had high levels of large-scale genetic connectivity, providing increased species-level resilience to localised disturbances. These results highlight the need to be wary of assigning species high vulnerability status based solely on their level of ecological specialisation.

Item ID: 29607
Item Type: Thesis (PhD)
Keywords: reef fish vulnerability; coral reef fishes; butterflyfishes; resilience; ecological specialisation
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2. Lawton, Rebecca J., Pratchett, Morgan S., and Berumen, Michael L. (2012) The use of specialisation indices to predict vulnerability of coral-feeding butterflyfishes to environmental change. Oikos, 121 (2). pp. 191-200.

hapter 3. Lawton, Rebecca J., Cole, Andrew J., Berumen, Michael L., and Pratchett, Morgan S. (2012) Geographic variation in resource use by specialist versus generalist butterflyfishes. Ecography, 35 (6). pp. 566-576.

Chapter 4. Lawton, Rebecca J., and Pratchett, Morgan S. (2012) Influence of dietary specialization and resource availability on geographical variation in abundance of butterflyfish. Ecology and Evolution, 2 (7). pp. 1347-1361.

Chapter 5. Lawton, Rebecca, Messmer, Vanessa, Pratchett, Morgan, and Bay, Line (2011) High gene flow across large geographic scales reduces extinction risk for a highly specialised coral feeding butterflyfish. Molecular Ecology, 20 . pp. 3584-3598.

Lawton, R.J., Wing, S.R., and Lewis, A.M. (2010) Evidence for discrete subpopulations of sea perch (Helicolenus ercoides) across four fjords in Fiordland, New Zealand. New Zealand Journal of Marine and Freshwater Research, 44 (4). pp. 309-322.

Lawton, Rebecca J., Pratchett, Morgan S., and Bay, Line K. (2010) Isolation and characterization of 29 microsatellite loci for studies of population connectivity in the butterflyfishes Chaetodon trifascialis and Chaetodon lunulatus. Conservation Genetics Resources, 2 (Supplement 1). 209-213.

Lawton, Rebecca J., Pratchett, Morgan S., and Bay, Line K. (2011) Cross-species amplification of 44 microsatellite loci developed for Chaetodon trifascialis, C. lunulatus and C. vagabundus in 22 related butterflyfish species. Molecular Ecology Resources, 11 (2). pp. 323-327.

Cole, A.J., Lawton, R.J., Pratchett, M.S., and Wilson, S.K. (2011) Chronic coral consumption by butterflyfishes. Coral Reefs, 30 (1). pp. 85-93.

Pratchett, Morgan S., Munday, Philip L., Graham, Nicholas A.J., Kronen, Mecki, Pinca, Silvia, Friedman, Kim, Brewer, Tom D., Bell, Johann D., Wilson, Shaun K., Cinner, Joshua E., Kinch, Jeff P., Lawton, Rebecca J., Williams, Ashley J., Chapman, Lindsay, Magron, Franck, and Webb, Arthur (2011) Vulnerability of coastal fisheries in the tropical Pacific to climate change. In: Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change. Secretariat of the Pacific Community, New Caledonia, pp. 493-576.

Cole, Andrew J., Lawton, Rebecca J., Wilson, Shaun K., and Pratchett, Morgan S. (2012) Consumption of tabular acroporid corals by reef fishes: a comparison with plant–herbivore interactions. Functional Ecology, 26 (2). pp. 307-316.

Pratchett, Morgan S., Bay, Line K., Coker, Darren J., Cole, Andrew J., and Lawton, Rebecca J. (2012) Effects of coral bleaching on coral habitats and associated fishes. In: Wildlife and Climate Change: towards robust conservation strategies for Australian fauna. RZS Forum Series . Royal Zoological Society New South Wales, Sydney, NSW, pp. 59-67.

Bene, Christophe, Lawton, Rebecca, and Allison, Edward H. (2010) "Trade Matters in the Fight Against Poverty": narratives, perceptions, and (lack of) evidence in the case of fish trade in Africa. World Development, 38 (7). pp. 933-954.

Date Deposited: 15 Oct 2013 02:30
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 100%
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