Transcript Island Syndromes in Plants

Island
syndromes
in plants
Aurea C. Cortes-Palomec
Hypothetical plant: Plantita
Many others
like Plantita
live in its
habitat
And
many
others
species
Herbivores
Seasonal growth
Seed dispersal
Plantita’s seeds got to Isla
It became a tree
Increased the size of its seeds
Development of separate plant “sexes”
Monoecious
Dioecious
History of many Island plants
Island Plant syndromes
Questions:
1) What are the main adaptive
syndromes present in island plants?
2) What are the environmental and
ecological factors present in islands
that favor the evolution of similar
traits?
Questions:
3) What are the advantages of developing woody
tissue? How does that affect the fitness of a
plant?
4) Why is it an advantage for colonizing plants to
exhibit high levels of seed dispersability but island
species to have reduced seed dispersability?
Questions:
5) How does the development of dioecy
contribute to the long-term persistence
of species in an island system?
6) What environmental factors lead to the
loss of competitiveness?
Chamaesyce degeneri
Coast. Mat-like tendencies, Small leaves, round and succulent
C. remyi
Rain forest
Large leaves, tree-shrub
C. celastroides
Tree, shrub
Lowland forest
Leaves small shed in dry,
hot weather.
Succulent stems store
water.
C. rockii
Cloud forest. Up to 8 m tall
Directional
change in
stature
increasing from
dry to wet
areas in
Chamaesyce
Honolulu
Sea level
703mm with dry season
during the summer
mean 23.3 C
Tantalus
408m
2520mm no dry season
mean 20 C
Oahu
Brassicaceae
Lepidium
L. virginicum
L. bidentatum
Plantago
P. major
usually rosette
P. princeps
long stem up to 1.5 m
Charpentiera
Deeringia
Factors that favor arborescence:
*Moderate climate and continuous growing
season allows continuous growth
*Mean temperature no lower than 10C can
be the threshold for arborescent species
in most areas (i.e. Hawaiian rain forest).
*Absence of extremes
*Absence of big herbivores
Dioecy:
Result from selection for
outcrossing
Avoid inbreeding
Dioecy:
World wide:
Ca. 4 % flora is dioecious
Hawaii:
Carlquist: 27.7 % is dioecious
Sakai: 971 native species
14.7% dioecious
20.7% dimorphic
Hawaiian flora:
Highest incidence of dioecy of any flora surveyed
Higher incidence of
dioecy in endemic
species than in
indigenous ones
More in older islands
(takes some time to
evolve)
Dioecy is significantly associated with
woodiness and hermaphroditism with
herbaceous habit
It is the result of both colonization of
dioecious species as well as evolution in
the islands.
Change in pollination syndromes:
In Hawaii there are few native bees
Only two species of butterflies
No bumblebees
One native terrestrial mammal (bat)
And only 50% of known orders of insects
15% of known families
Small green or white flowers are
abundant -- these colors are presumably
associated with pollination by wind or
unspecialized insects.
Reduced number of specialized floral
syndromes
Favor unspecialized dioecious flowers
Change in dispersal mechanism
Bidens
Bird dispersal (coast)
to
Wind dispersal (inland)
Bidens pilosa to B. torta
Ancestral
Derived
Euphorbia celastroides
(Sticky seeds)
E. clausidefolia,E. rockii
(non-sticky)
There is also an
increase in seed
size
If you are too big
birds can not eat
you!!!
Chamaesyce
Gigantism (Large seeds)
Erythrina
usually dispersed by water, in Hawaii
they can not float anymore (E.
sandwicensis)
Advantages of an increase in seed size:
* Poor dispersal favors establishment near the
parental plant
* Immigration towards wet forest where poor
dispersability is common
* Larger seeds better adapted to grow in shade
* Change in habitat leads to loss of contact with
the agent of dispersion so the ability is lost
Loss of competitiveness:
* No mechanical defenses, no scented oils
(i.e. odorless mints in Hawaii, mints are insect
repellents)
* Hawaii species are less competitive than
continental species
Develop in a safe herbivore-free environment
Rhus
Rhus sandwicensis
Rubus hawaiensis
Not physical defenses
Pritchardia
Its seeds are not protected, now it is endangered due to
the presence of the Polynesian rat
* No poison plants..... no big
herbivores therefore not
needed
* No evolutionary pressure
on them so they were lost
On islands, initially, more sites available, some
similar to those of the ancestors and some totally
different leading to speciation
Questions:
1) What are the main adaptive
syndromes present in island plants?
*Arborescence
*Dioecy
*Reduced competitiveness
*Reduced dispersability
Questions:
2) What are the environmental and
ecological factors present in islands that
favor the evolution of similar traits?
* Continuous growing season
* Lack of herbivores
* Presence of different microclimates
* Lack of recolonization
Questions:
3) What are the advantages of developing woody
tissue? How does that affect the fitness of a
plant?
* Increase in size => More competitive
* Perennial => More seeds
* Larger investment on seeds
Questions:
4) Why is it an advantage for colonizing plants to
exhibit high levels of seed dispersability but
island species to have reduced seed
dispersability?
High dispersability => Reach the island
Low dispersability => Stay in the island
Questions:
5) How does the development of dioecy
contribute to the long-term persistence
of species in an island system?
* Introduce out crossing
favoring genetic variability
Questions:
6) What environmental factors lead to
the loss of competitiveness?
* Less herbivores
* Less predation
* Less density
=> Very susceptible to alien flora