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Predicting future vulnerabilities of the reef coral phylogeny

Phylogeny, extinction risks and conservation, The Royal Society, London, 10 March 2014

Danwei Huang

on 5 June 2014

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Transcript of Predicting future vulnerabilities of the reef coral phylogeny

Random distribution of risk does not reduce phylogenetic diversity substantially
Huang (2012, PLoS ONE)
Evolutionarily Distinct
Globally Endangered
) corals

ED = 0.5 + 0.2 + 0.33 + 1 = 2.03
ED = 0.5 + 5 = 5.5
ED = 2.5 + 1 + 2 = 5.5
Based on EDGE (Isaac et al. 2007, PLoS ONE)
evolutionary distinctiveness (ED)
of species to aid conservation prioritisation

Huang (2012, PLoS ONE)
1293 Scleractinia spp.
837 reef corals (complete)
456 non-reef corals (64%)
Least Concern (GE ~0.1%)
Near Threatened (GE ~1%)
Vulnerable (GE ~10%)
Endangered (GE ~67%)
Critically Endangered (GE ~99%)
Predicting future vulnerabilities of the reef coral phylogeny
Danwei Huang
Kaustuv Roy

McCarthy et al. (2012, Science)
~$1 billion/year needed to reduce extinction risk of all threatened bird species

Currently, only 12% funded
Barnosky et al. (2011, Nature)
Limited resources impose practical limitations on conservation.
Therefore, we need to prioritise species/regions for conservation.
Based on what?
Coral reefs are declining on a global scale
Cadotte et al. (2011, J. Appl. Ecol.)
Most communities show ecological redundance
(i.e. different species fill similar ecological niches and contribute to similar ecosystem function)
Cayman Islands fish food web
Species performing unique ecosystem functions
(e.g. the few top predators on reefs)
"Quite apart from many theoretical and practical problems that continue to affect the species concept and its application, is it appropriate for conservation purposes to regard all species as equal in this manner? To a conservationist, regardless of relative abundance, is
equal to a species of
? Is the panda equivalent to one species of rat?"
ED = length of species' terminal branch plus species-weighted shares of ancestral branches
Prerequisites for assessment
1. Majority of species assessed by IUCN for
threat status
2. Complete sampling of
evolutionary tree
(species and branch lengths)
1. Majority of species assessed by IUCN for
threat status
2. Complete sampling of
evolutionary tree
(species and branch lengths)
= probability of extinction in the next 100 years
3 Critically Endangered
16 Endangered
11 Vulnerable
(e.g. genera with single species)
Main Caribbean reef builders with high functional value
Species from all major reef regions
Veron et al. (2011)
Clustering of risk on the tree of life can lead to large declines in phylogenetic diversity
Corals susceptible to individual threats are closely related
Are risks clustered on the coral tree of life?
To qualify as mass extinction event: at least 75% of species loss within a short geological time frame (~2 Ma); has there been extinctions in recent times, and do they constitute mass extinction

Current extinction is low, but include threatened species (according to the IUCN Red List, discussed later), nearing 75%; high potential mass extinction event if we don't do anything to avert disaster
Tree information: (1) shape; (2) branch lengths
Acropora cervicornis
10 March 2014
Stony corals
~1550 spp.
~55% reef

Dunn et al. (2008, Nature)
Ecological redundance, e.g. predator with many different prey, so removing a single prey species not decreasing ecosystem function much; to prioritize according to functional value is to preferentially protect species that have unique function(s) with many links to other species that once lost can lead to large losses of function.

Corals much more difficult: as a whole keystone, but roles individual species play are not obvious.
IUCN: International Union for Conservation of Nature publishes Red List of Threatened Species, soliciting expert opinion based on empirical trends and biology for every species, assigning threat status; started publishing lists in late 1990s, now only about 5% of all known species assessed.
Threatened species are not clustered on the tree
Huang (2012, PLoS ONE)
More clustering = greater loss of phylogenetic diversity?
Total length of at-risk branches
= (2 + 1 + 1)
+2+ 1
= 7
Total length of at-risk branches
4 + 2 + 1
= 7
Huang & Roy (2013, Ecol. Evol.)
Scleractinia: 4 CR, 23 EN, 198 VU, 174 NT, 289 LC
(2008, Science)
Polyps, skeleton, symbionts (zooxanthellae + microbes)
Guest et al. (2012, PLoS ONE)
Willis et al. (2004)
Kayal et al. (2012, PLoS ONE)
Hughes et al. (2010)
The delicate symbiosis between the coral host and zooxanthellae is broken primarily by increased temperatures. The global rise in sea surface temperatures has led to longer periods of exposure to heating beyond physiological tolerance levels of reef corals, resulting in large tracts of reefs being bleached. The symbiotic balance with microbes--bacteria and viruses--can also be destroyed, leading to a multitude of diseases. Local impacts such as eutrophication have been implicated in outbreaks of predatory CoTs.
Ecosystem function
Huang & Roy (2013, Ecol. Evol.)
Huang & Roy (2013, Ecol. Evol.)
Veron et al. (2011)
... 1000 x
Faith (1992): The phylogenetic diversity (PD) of s [a subset of taxa] is equal to the sum of the lengths of all those branches that are members of the corresponding minimum spanning path.
Parhar & Mooers (2011, PLoS ONE)
~ excess PD loss
Helmut (2007): Phylogenetic species variability summarizes the degree to which species in a community are phylogenetically [un]related.

For a hypothetical neutral trait:
0 = no variability
1 = maximum variability
High richness
=> High PD
≠> High/low PSV
High richness
=> High risk!
High richness
≠> High PD loss
≠> High PSV loss
Fixed effect: species richness
Random effect: phylogeny
SW Western Australia
Johnston Atoll
Pacific Costa Rica & Panama
Loss of deep branches
=> high PD loss

Loss from one part of phylogeny
=> species more more closely related on average
=> high PSV loss
1. Pacific Costa Rica & Panama
2. Johnston Atoll
3. SW Western Australia
Loss from one part of phylogeny
=> species more more closely related on average
=> high PSV loss

Deep branches preserved

But functional diversity at risk
Loss of deep branches
=> high PD loss

Balanced loss
=> low PSV loss
Loss of deep branches
=> high PD loss

Loss from one part of phylogeny
=> species more more closely related on average
=> high PSV loss
Loss of 'complex' corals
Loss of 'robust' corals
Limited resources force us to prioritise for conservation
Species: quantify species' historical value in combination with threat status
Global: assess distribution of threats on the phylogeny
Regional: predict relative losses of phylogenetic diversity and variability
Problems with EDGE analysis

1. Use of ED does not take into account the fact that species share all branches, except the terminal one, with other species on the tree. During extinctions, every branch is either lost or not, and not lost in fractions as ED implies. Rather than making static allocations of conservation value, we should focus on avoiding worst case losses by estimating impacts on the tree based on projected extinctions.

2. Species ranks are not very useful for reef conservation, which generally focuses on areas instead of taxon sets, i.e. no panda of reefs. Corals are discussed as a whole as reef-builders, rather than isolated cases of threatened species.
Reef corals: predicting outcomes of the evolutionary diversity

1. Individual species
2. Globally: how threats put the tree of life at risk
3. Regionally: how outcomes can vary dramatically
Reefs formed mainly by corals, colonial sessile animals that build a calcium carbonate skeleton.
Chemistry of calcification is mediated by the coral's endosymbiotic relationship with dinoflagellate algae Symbiodinium (zooxanthellae), thus limiting their distribution to 30NS, and only in areas that are shallow.
Health greatly influenced by symbioses, with zooxanthellae and also microbes (bacteria and viruses) that are in close association.
Evolutionarily Distinct
Globally Endangered
loss of 1/3 branch?
loss of 1/4 branch?
Save these corals!
1. Massive coral
2. Another massive coral
3. Branching coral
4. Yet another massive coral
5. ...
To make concept of evolutionary diversity more applicable for coral conservation, we need to focus on regional scale, at which MPAs are being implemented.
loss of deep branches
Regional level, the most applicable to reef conservation
Information can help reef managers carry out conservation planning to preserve the long-term diversity and function of coral reefs
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