Transcript Temporal Radiations

Temporal Radiations
Conservation Biology 55-437
Lecture 3
Feb. 26, 2010
Species radiations
The opposite of extinction is radiation – speciation
diversifying a taxon.
Toads: subcosmopolitan distribution
Cape Leopard toad (South Africa)
Pebas stubfoot toad (South America)
American toad (North America
Van Bocxlaer et l. 2010. Science 327: 679−682
Traits
Context
Adults
(Semi-)terrestrial adult niche (according to IUCN
No dependency on constant water or humidity
data)*
Large body size
Higher relative water storage ability in bladder
Presence of parotoid glands*
Enhanced toxicity and rehydration ability
Presence of inguinal fat bodies*
Extra energy reserve (extra fat storage ability)
Reproduction and development
Aquatic, opportunistic oviposition site*
Ability to use all kinds of water bodies, including those
in harsh habitats
Large clutch size
Typical feature of r-strategy
Exotrophous larvae*
Limited maternal investment in larval nutrition
Case Study:
The Cane Toad Bufo marinus
Galapagos Islands: Most islands are not occupied; Darwin
visited the islands in 1830; Cocos Island is 600km NE
26 species of land birds occurred naturally on the
Islands before human introductions; 13 of these
are finches. The islands also support 4
mockingbird, 2 flycatcher, 2 owl, 1 hawk, 1 dove, 1
cuckoo, 1 warbler and 1 martin species (Pianka
1983)
The island finches belong
to a distinct subfamily of
finches, endemic to the
Galapagos and Cocos
Island (Costa Rica). Cocos
Island supports only 1 finch
species, the Cocos Island
finch Pinaroloxias inornata.
Phylogeny
• Warbler finch may be the ancestral species, not the Cocos finch,
which groups with the tree finches.
Sato et al. 1999 PNAS 96:5101−5106
On the Galapagos Islands, adaptive radiation has resulted from
geographic isolation and reduced gene flow among islands.
Three distinct genera (Geospiza, Camarhynchus and
Certhidea) occur on the islands.
Members of these genera differ in where they forage, how they
forage, and what they eat.
Finch diversity by island
Tree finches
The 6 species of Camarhynchus finches
forage in trees, have narrower beaks,
and eat either vegetation (1 species) or
different sizes of insects. C. pallidus
uses a stick or cactus spine to probe for
insects.
Ground finches (Geospiza)
These species are similar in coloration -- adult males
are black, and females streaked brown. They all have
bills of the "crushing" variety, useful for feeding on
seeds.
The ‘Vampire Finch’ Geospiza difficilis septentrionalis
Character Displacement
differences among similar species are accentuated in regions
where the species co-occur but are minimized where the
species’ distributions do not overlap.
On islands where Geospiza fuliginosa and G. fortis occur
sympatrically, they tend to have widely divergent beak
depths.
Only one of these species is on each of
Daphne and Crossman. The beak
morphologies are very similar when the
species occur in isolation.
Before it can be confirmed that character displacement
has occurred, 4 conditions must be met:
1) the change in mean character state in areas of overlap
should not be predictable from variation within areas of
isolation
2) sampling should occur at more than one set of
locations to eliminate local variation effects
3) Heritability of the feature must be high if genetic
variation is thought to underlie variation in the feature,
and if it is to be passed to subsequent generations
4) Evidence must be presented to demonstrate that
competition occurs and that the measured feature has
relevance to competition among groups
 1) the change in
mean character state
in areas of overlap
should not be
predictable from
variation within areas
of isolation
 3) Heritability of the
feature must be high if
genetic variation is
thought to underlie
variation in the
feature, and if it is to
be passed to
subsequent
generations
G. fortis & G. scadens on Daphne Major
(Grant & Grant 1993, Proc. R. Soc. Lon. B)
rainfall on Daphne Major
seed size (white) and hardness (black)
fortis (top), scandens (bottom)
Strong selection for G. fortis,
which feeds on small seeds, over
G. scandens, which feeds on
rare cactus seeds, following
drought after 1983
G. fortis on Daphne Major (Boag & Grant 1981, Science)
• 1500 birds banded and studied between 1975-78
• regular rainfall (large finch populations) until 1977, when only 24mm
rain fell. G. fortis did not breed and 85% decline in population (A);
seed abundance declined (B), big males survived best (C),
corresponding with decline of small seeds (D)
Grant & Grant (2002) Science paper
• studied the same populations of G. fortis (medium ground
finch) and G. scandens (cactus finch) on Daphne Major
for 30 years
• survival of marked and measured individuals measured
each year
• 6 traits studied were reduced by Principal Components
Analysis, which break down as body size, beak size and
beak shape
If species were not changing,
each measures should have
stayed within its original 95%
confidence interval (horiz.
lines). Clearly this is not
happening. G. scandens
converged on G. fortis'
morphology
1. body & beak sizes selected
more than beak shape
2. species differed in net selection
direction on size traits
3. unidirectional selection (up to 3
yrs) occurred in both species
4. selection events in the species
were not synchronized except
in late '70s during a drought
5. each of these studied traits was
highly heritable, so evolution
followed for fortis (body size,
beak size, beak shape) and for
scandens (body size, beak
size)

4. Evidence must be presented to
demonstrate that competition
occurs and that the measured
feature has relevance to
competition among groups
There is, however, no way to deal with
criterion 2 since there is only one Daphne
and one Crossman. Satisfying this
requirement would necessitate observing
the same pattern on other islands like
Daphne and Crossman.
Large-beaked G. fortis (A) and G. magnirostris (B) can crack or tear
the woody tissues of T. cistoides mericarps (D), whereas small-beaked
G. fortis (C) cannot
G. fortis
P. R. Grant et al., Science 313, 224 -226 (2006)
Aging the Hawaiian Islands
Fleisher et al. (1998) Mol. Ecol.
Hawaiian honeycreepers
These birds experienced much greater adaptive radiation
than Darwin's finches, though, sadly, many of the taxa
have been driven extinct due to introduction of diseases,
other passerine birds and mammals, and destruction of
habitat.
On Laysan Island introduced rabbits and a windstorm
destroyed vegetation resulting in the extinction of the
Laysan honeycreeper.
Bird pox virus and avian malaria (introduced to the
Hawaiian islands by mosquitoes on ships in 1826) have
caused sharp declines in Drepanidid species, including
the honeycreeper.
wide diversity, some now extinct (E)
beak shape
highly variable
and highly
adapted to
feeding mode
Origin of the Honeycreepers
• Johnson et al. (1989) used starch gel electrophoresis to
study 8 genera (9 species) of honeycreepers
• they are a monophyletic group (only one ancestor)
• the ancestral species colonized the Hawaiian archipelago
7-8 million yr ago
• this agrees with the emergence of Nihoa (now largely
submerged) but predated the island of Kauai (5 MYBP)
• Oreomystis and Paroreomyza are the oldest and most
diverse lineages
• youngest lineages are the nectar feeders and thick billed
finch types
Time difference between island formation
dictates genetic distance between species
Hawaiian Flycatchers: VanderWerf et l. Conservation Genetics 2009
• Currently, honeycreepers occur primarily at altitudes
above 600 m on the main islands and on several
smaller remote islands in the NW part of the
archipelago.
• Mosquitoes, by contrast, occur primarily below 600 m,
and overlap very little with the honeycreepers.
• At the lower altitudinal end of the honeycreeper
species ranges, between 2 and 7% of individuals have
avian malaria.
• in total, 28 of 53 known species are extinct (34 known from
historical records, 19 from fossil records)
• 18 of the remaining species are endangered
• 9 extinctions have occurred since introduction of malaria to
the islands. Of these, 6 occurred on Lana'i, Moloka'i and
O'ahu. These islands have been radically modified by
humans, thus habitat destruction appears to have played a
large role.
• Behaviour may have affected 2 large, nectar-feeding
Drepanidid species driven extinct and 2 smaller ones
extirpated ('akoekoe and 'i'iwi) on some islands.
• The rare 'akiapola'au, a specialized insectivore, has
become endangered because it lives primarily in large koa
trees; koa trees have been widely harvested for furniture
lumber.
• Another endangered species, the palila, a granivore,
exploits seeds of one tree, the mamane. This tree has
been adversely affected by introduced goats and sheep,
thereby endangering the bird.
• Honeycreepers are endangered
because of their extreme
specialization (habitat or food),
which itself is a result of
dramatic adaptive
radiation. This problem may be
compounded by introduced
diseases, mammals, and exotic
birds.
What's the Honeycreeper's Future?
Benning et al. (2002) PNAS
• habitat loss began with the Polynesian colonists (9001000 yrs ago), who cleared low elevation and seasonally
dry forest
• European colonists brought new agricultural technology,
domesticated cattle
• hunting, beginning with Polynesians, and introduction of
dogs and rats that preyed on nesting birds. These
predators were followed by mongoose, cats and 2 more
rat species
• introduction of mosquitoes and of avian pox, and more
recently avian malaria, had the greatest consequences
Temp. <13°C is critical to prevent malaria infection. In Hanawi Forest
(Maui), a 2°C increase would cut this zone area by half (665 to 285Ha).
low mosquito risk zone, Hanawi, Maui
low mosquito risk zone, Hakakau Refuge, Hawaii
(low risk areas declines from 3120 to 130 HA)
Alakai Swamp, Kauai. No area currently below 13°C,
area of possible high risk moves up 300m. Must focus
on disease prevention in remaining honeycreeper
populations.
Hawaiian Drosophila
More than 900 endemic species, each typically restricted
to one island.
Speciation of these flies is also speculated to have
occurred as a result of adaptive radiation.
Each species has individual preference for mating
ceremonies and territories which involve factors of light,
temperature, and humidity
Differences in food sources-
herbaceous v. carnivorous
Body, wing size and shape
• Adaptive situations often cause plants to
evolve the available pollinators, such as
changing insect spp., to birds, etc.
• Point: Radiations can affect multiple levels – a
waterfall
Flower
Cyrtandra
Leaf
Fruit