Introduction
Methods
Methods/Results I
Results II
Discussion
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Chaetodon is a genus of this
Butterflyfishes
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This is the objective of the study
To investigate the bottom-up effects of climate-induced disturbance (mass coral mortality) on reef fishes.
100
This diagram represents what
Possibilities of dietary overlap in reef fishes.
100
This graph shows what
Changing dietary preference with coral cover loss in butterflyfish species. Less coral cover= less preference
100
These are the reasons that we can attribute observed butterflyfish feeding behaviour to coral availability ONLY
1) The warming sea temperatures were not significant enough to affect butterfly fish behaviour- so warming temps not affecting them
2) No predation of butterflyfish was observed- so predators not influencing their behaviour
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This occurs when warming seawater temperatures cause coral to turn white and die.
Coral bleaching
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These were the years that sampling took place in
2016- warmer temperatures but no bleaching-related death (pre-mortality)
2017- bleaching evident, mass coral mortality (mortality)
2018- two years after bleaching (post-morality)
200
These were quantified using Hurlbert's Probability of Interspecific Encounter (PIE)
1) Evenness of coral assemblages
2) Evenness of coral being eaten by butterflyfish
200
Weakened dietary preferences had this effect on butterflyfish niche overlap in 2017 (year of mass coral mortality).
Overlap slightly higher than random, fish switched from the dead Acropora coral to Montipora spp.
200
This is the recovery time of a bleached coral reef without disturbance.
7-29 years
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This genus of hard coral is more sensitive to bleaching than other genera, and is the preferred food source of butterfly fish.
Acropora
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This method was used to estimate butterfly fish abundance and coral cover.
A 50m line-transect along the most active part of the coral
1) Counted fish on either side of the transect
2) Identified coral species along the transect
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This change in dietary preference happened when food availability decreased (65% of coral cover lost).
Butterflyfish dietary preference decreased.
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Weakened dietary preferences had this effect on butterfly niche overlap in 2018 (two years post-bleaching; one year post-mortality)
Decreased overlap; fish now ate a variety of coral genera. Matched random resource use.
300
This is the average frequency (in years) of coral bleaching events.
Once every 6 years as of 2016
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This is the definition of "bottom-up effects".
When changes in food availability cause behavioural changes in predator species.
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This was the method used to record butterflyfish diet
Picking a focal fish and stalking it for three minutes. They recorded:
- Every bite taken
- The coral species that was bitten
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This graph shows what
Evenness of coral assemblages compared to evenness of coral being eaten by butterfly fish.
After bleaching- fish diet is more even (they're less picky in the coral they're eating; eating a wider range of genera)
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This graph shows what.
Histogram- niche overlap if random
Black line- niche overlap observed. Here, before bleaching-related mortality there is very high overlap.
400
Contrary to theoretical expectations, this was the result of weakened dietary preference in butterflyfish on niche overlap
Decrease in niche overlap (competition)
500
This is the definition of "dietary expansion"
Assuming constant competitor abundance:
When food availability is low, foragers should expand their dietary breadth (they become less picky in what they eat).
Being less picky can lead to increased resource overlap, which may lead to increased competition.
500
These are the hypotheses of the study
1) Butterflyfish should show weakened dietary preferences (get less picky) in response to less food availability.
- 1a) If large changes in dietary evenness (the fish becoming less picky) are not accompanied by large changes in coral evenness (coral assemblages stay the same), then the fish are changing their dietary preferences.
- 1b) Did loss in coral cover affect individual dietary preference?
2) Weakened dietary preference (fish becoming less picky) should lead to increased dietary overlap and more competition
500
This graph shows what.
Loss of hard coral cover after bleaching event.
500
These graphs show what
Niche overlap after coral mortality.
2017- year of coral mortality- very high
2018- 1 year after mortality- very low
500
These are limitations of looking at the short-term effects after coral bleaching
Butterflyfish are long-lived, we don't know if:
1) They'll maintain dietary flexibility for long
2) Future generations will be affected
3) Continued coral mortality will decrease overall availability of food and cause population decline in the future