Reproductive Biology of the Endangered Shrub,
Fremontodendron californicum subsp. decumbens,and its Conservation Implications
Robert BoydDepartment of Biological Sciences
Auburn University
• 3 taxa recognized• Species, or
subspecies Fremontodendron californicum– Note F.
decumbens,1 site in El Dorado County, CA
Fremontodendron californicum subsp. decumbens
• Found only near Pine Hill
• 2,000 shrubs (<1 mi radius)
• Listed federally endangered 1996
Pine Hill from SE
Closer view Pine Hill chaparral
F. californicum subsp. decumbens
• Small shrub• 1-2 meters tall
F. californicum subsp. decumbens
• Beautiful flowers• Fruit covered with
stiff trichomes• Seeds: orange
appendage (elaiosome)
Study: Reproductive Biology• Document reproductive
attrition• Mark flower buds• Determine fates
Marking flower budsin spring
Bud markedwithwire atits base
Reproductive Biology• Answer: insects attack flower
buds, flowers, fruits• 1.8% flower buds survive to
produce seeds
Reproductive Biology• Seed fates• Predation: marked seeds
(elaiosomes removed) in caged and uncaged locations under shrubs
• After 9 mo: extract & count surviving seeds
• Difference between locations: rodent predation
Basic Reproductive Biology• Seed fates: Predation• Answer: 90% seeds
eaten by rodents
Reproductive Biology• Seedling fates• Seeds dormant unless
heat-treated• Plant heat-treated
seeds in caged and uncaged plots
• Document fates in each case
Reproductive Biology• Seedling fates• Answer:
– Rodents eat some– Insects eat most– Rest die from summer
drought
Placerville CA rainfall
Reproduction Model
Today’s story• Pollination: insect visitors to flowers• Dispersal: ants attracted to elaiosomes • Focus on pollination and seed dispersal
– Important life cycle stages– Involve mutualist animals
Today’s story• Pollination: insect visitors to flowers• Dispersal: ants attracted to elaiosomes • Focus on pollination and seed dispersal
– Important life cycle stages– Involve mutualist animals
• What roles mutualists in plant reproduction?
• Conservation implications?
Focus on pollination• Are insect visitors
required to make fruits?
Focus on pollination• Approach: enclose
branches to prevent insect visits
• Mark flowers already open (one color wire)
• Mark large flower buds (another color)
Focus on pollination• Are insect visitors required to make fruits?• 39 flower buds, 0% fruits• 22 flowers open when bagged, 32% fruits• Answer……..
Focus on pollination• Are insect visitors required to make fruits?• 39 flower buds, 0% fruits• 22 flowers open when bagged, 32% fruits• Answer: Yes, visits required.
Focus on pollination• What insects visit flowers? Which are likely
pollinators?
Focus on pollination• What insects visit flowers? Which are likely
pollinators?• Approach: watch flowers, document visitors• June: two years• 1,746 insect visits.
Focus on pollination
Tetralonia stretchii 89.4%
Callanthidium illustre 8.7%
Apis mellifera 1%
Other native bees 2%
Bee species Percent visitsAnswer: Native solitary bees
Focus on pollination• Dominant visitor:
Tetralonia stretchiiStretching for nectar
Gathering pollen
Nectaries
Focus on pollination• What insects visit flowers? Which likely
pollinators?• Answer: Native solitary bees.
Focus on pollination• How effective are bees?• Approach: compare fruit set and seed set hand-
pollinated flowers.
Focus on pollination• Fruit set not significantly different:
– Hand-pollinated 80% Bee-pollinated 70%
Focus on pollination• Fruit set not significantly different:
– Hand-pollinated 80% Bee-pollinated 70%
• Seed set different:– Hand-pollinated: 4.9 seeds/flower– Bee-pollinated: 2.6 seeds/flower
Focus on pollination• Fruit set not significantly different:
– Hand-pollinated 80% Bee-pollinated 70%
• Seed set different:– Hand-pollinated: 4.9 seeds/flower– Bee-pollinated: 2.6 seeds/flower
• Answer: All flowers pollinated, pollen amount not maximized (seed set 53% of possible).
Focus on pollination• How bees find flowers?• Approach: UV photos
Focus on pollination• How bees find flowers?• Approach: UV photos
UV lightAll light
Focus on pollination• Summary:
– Native solitary bees essential to seed production
– Not maximizing seed set, but maximizing fruit set.
Focus on seed dispersal• The ant connection
– Harvester ant: Messor andrei– Attracted to elaiosomes, carry seeds to nests
(in openings chaparral)– Discard some seeds on “midden”
Focus on seed dispersal• How do ants modify reproductive attrition?• How does ant dispersal benefit plant?
Focus on seed dispersal• Possibilities:
– 1) Do ants stimulate seed germination (scarify seeds)?
Focus on seed dispersal• Possibilities:
– 1) Do ants stimulate seed germination (scarify seeds)?
– 2) Do ants protect seeds from rodent predation by moving them from under shrubs to open areas?
Focus on seed dispersal• Possibilities:
– 1) Do ants stimulate seed germination (scarify seeds)?
– 2) Do ants protect seeds from rodent predation by moving them from under shrubs to open areas?
– 3) Do seedlings on ant middens have better chance survival?
Focus on seed dispersal• Possibilities:
– 1) Do ants stimulate seed germination (scarify seeds)?
– 2) Do ants protect seeds from rodent predation by moving them from under shrubs to open areas?
– 3) Do seedlings on ant middens have better chance survival?
– 4) Do benefits occur after fire stimulates seed germination?
Focus on seed dispersal• 1) Do ants stimulate seed germination (scarify
seeds)?• Compare germination of seeds
– Fresh from fruits– Given to ants and recovered from midden.
Focus on seed dispersal• 1) Do ants stimulate seed germination (scarify
seeds)?– No statistical difference
2.6% 54%
5.4% 66%
Untreated seeds Heat-treated seedsFresh seeds
Ant-handled seeds
% germination
Focus on seed dispersal• 2) Do ants protect seeds from rodent predation
by moving them from under shrubs to open areas?
Focus on seed dispersal• 2) Do ants protect seeds from rodent predation
by moving them from under shrubs to open areas?– Seed trays in pairs– Canopy edge, 0.5 m, 1 m away in open– Seeds with elaiosomes one tray, without in other
Focus on seed dispersal
– Compare seed removal– No effect distance– More with elaiosomes taken
elaiosomeno elaiosome
Focus on seed dispersal• 2) Do ants protect seeds from rodent predation
by moving them from under shrubs to open areas?– No, seeds not more safe in open– But removal elaiosome helps seeds avoid rodent
predation– This benefit of ant handling, but not benefit of
elaiosome presence.
Focus on seed dispersal• 3) Do seedlings on ant middens have better
chance survival?– Plant heat-treated seeds on middens and under
shrubs– Cage some to protect from rodents
Ant midden Under shrub canopy
Focus on seed dispersal• Results: Mean seedling longevity in days (SD)
27 (23) 46 (30)
17 (20) 34 (27)
Ant midden Canopy
Caged
Uncaged
Caging helps, survival on middens is less!
Focus on seed dispersal• 4) Do benefits occur after fire stimulates seed
germination?• Approach: experimental burn!
Focus on seed dispersal• 4) Do benefits occur after fire stimulates seed
germination?• Preparation/planning!
Focus on seed dispersal• 4) Do benefits occur after fire stimulates seed
germination?
Focus on seed dispersal• 4) Do benefits occur after fire stimulates seed
germination?
Aerial view Ground view
Focus on seed dispersal• Seedlings counted & marked during winter
(rainy) season following fire• Most under canopy/at canopy edge
Focus on seed dispersal• Survival higher away from canopy
Focus on seed dispersal• Why?• 1) Rodent predation greater
under canopy
Focus on seed dispersal• Why?• 2) Dispersed more likely near opening
created by death of shrub• Many chaparral shrubs re-sprout after fire,
including Fremontodendron
ResproutingFremontodendron
Focus on seed dispersal• Measure distance each seedling to nearest:
– Re-sprouting shrub– Dead shrub
• If nearer dead than live: close to opening
Near dead…Mostly dead
Focus on seed dispersal• Measure distance each seedling to nearest:
– Re-sprouting shrub– Dead shrub
• If nearer dead than live: close to opening
Near to dead: not same as “mostly dead”…..
Focus on seed dispersal
Dead chamise shrub
Fremontodendron seedlings
Focus on seed dispersal• Summary dispersal benefits (after fire):
– 1) Less rodent predation– 2) Greater chance being near opening in
chaparral community.
Conservation Implications
• Pine Hill Reserve small (97 hectares)
• Surrounding area being developed
Clearedarea west ofPine Hill
Conservation Implications• Pollination
– Native bees required– These bees generalists
Conservation Implications• Dangers
– How big reserve needed to protect bees?– Neighborhood activities may threaten bees
• Insecticides off Reserve could harm bees• Plantings off Reserve could draw bees away
Solution:monitorpollinationsuccess
Conservation Implications
• Seed dispersal– Native ants required– Benefits accrue only after fire
Conservation Implications
• Seed dispersal– Native ants required– Benefits accrue only after fire
• Dangers– How big reserve needed to protect ants?– How land use in neighborhood affect ants?
• Land clearing, insecticide use, etc.
Final lessons for endangered species management
• Consider these questions, plan for periodic fire (stimulate germination)
• 1) Mutualists important
Most rare plants don’t have pollinators/dispersersidentified
Final lessons for endangered species management
• 1) Mutualists important• 2) Habitat protection best way to
maintain web of life• 3) Managers must integrate biology
with human needs/habitat uses
Final lessons for endangered species management