1
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions 1
Granivory
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Seeds ! Pre-dispersal (inverts)
< Post-dispersal losses (verts)
! Intensity of the two are positively correlated by attractive features – Poor chemical
defenses, nutritious rewards
2 See Table 5.1
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Nutrient rewards
3 Fig. 5.1
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Seed Defense
4
Fig. 5.2
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Fleshy Fruit Seed Content
5 Fig. 5.3
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Chemical Defense ! Non-protein amino acids,
cyanogenic glycosides, protease and amylase inhibitors
! Effects must be studied in taxa-specific manner – E.g. Jojoba (Simmondsia
chinensis) seeds on 2 mice (Perognathus penicillatus vs. P. baileyi)
6
2
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Life-History Variation in Seed Prod’n
7
Fig. 5.4
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Granivore Guilds
8
Fig. 5.5
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Vertebrate Adaptations
! Mostly behavioural ! Rodents store caches of
seeds ! Red Crossbills (Loxia
curvirostra) morphology may favour efficiency with one type of seed however forage on a variety
9 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Post-Dispersal Granivory
10
Fig. 5.6
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Determinants of Granivory ! Attractants at long vs. short range ! Granivores should demonstrate Optimal
Foraging – Costs: handling time, transport, detox – Benefits: nutrient content, quality
! Mediated by – Seed traits: mass, shape, energy, toxicity – Granivore traits: body size, susceptibility to toxins,
olfactory acuity, hunger – Habitat characteristics: seed distribution, soil
texture, physical environment 11
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Frequency Effects
12
Density Independent
Box 5.1
3
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Frequency Effects
13
Density Dependence
Box 5.1
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Frequency Effects
14
Direct Dependence
Box 5.1
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Other Positive Effects ! Inter-year
– Can have a numerical response in granivore populations due to good seed crop increasing offspring survival
– Increased predation the following year ! Residence time
– Granivores attracted more towards patches with high seed crop and stay longer
– Disproportionally great seed removal in these cases compared to small patches
15 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Post-Dispersal Density Effects
! Removal rate of small seeds by generalists increases with seed production
! Large seed removal rates relatively density-independent – Limited by handling
time 16
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Effects of Other Food Sources
! Positive – Losses in Douglas Fir
(Pseudotsuga menzisii) greater when squirrels can rely on other conifer seeds in rare times
! Negative – Losses lessened if
neighbouring species’ seeds are more attractive
17 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Granivory Effects on Plants
! Will be small if – Vegetative reproduction important – Large and persistent seed bank – Granivores can be satiated – Plant colonization limited by site
characteristics, rather than seed production – Granivore population limited by factors other
than seed production
18
4
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Regeneration Strategies
19 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Masting Effects
20
Fraxinus excelsior
Fig. 5.8
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Granivore Effects on Plants ! Larder-hoarding ! Scatter-hoarding
21 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Interactions Pre- & Post-Dispersal
! Some animals avoid attacked seeds – Jays, mice avoid weevils – Not squirrels
! Many frugivores react to colour changes in attacked fleshy fruit – Some deterred – Some attracted
22
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions 23
Janzen-Connell Hypothesis Fig. 5.9
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions 24
Rodent Recovery Potential
Fig. 5.10
5
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Effects on Plant Community
! Trade-off between granivory and plant competitiveness
! Frequency dependence ! Spatially heterogenous granivory ! Janzen-Connell hypothesis
25 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions 13:38
26
Granivory and Natural Selection
Num
ber o
f Ins
ects
Key Largo
Wales Lake Florida
Beak Length (mm)
! Soapberry bug (Jadera haematoma)
! Round fruit native, flat fruit introduced
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Seed Effects on Granivores
! Darwin’s Finches (Geospiza) on Daphne Island
! Drought in 1977
27
Num
ber o
f fle
dgel
ings
Beak Width (mm)
N = 90 4
8
30 60 90
N = 751
All birds on Daphne (1976)
Survivors (1978)
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Trade-Offs in Seed Production
! Between quality and quantity ! Between frugivore attraction and
deterring seed predators ! Between satiating seed predators and
saturating mutualist seed dispersers ! Between investing in seed nutrition vs.
protection
28
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Economy of Scale
29 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Insect Adaptations to Asynchrony
! Risk-spreading diapause – Progeny with mixed diapause
lengths ! Predictive Diapause
– Emergence from diapause triggered by environmental cue coinciding with seed production
30
6
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Serotiny ! Retention of seeds until
environmental trigger ! Advantages
– acts like masting – seedling establish in
appropriate conditions ! Disadvantage
– Predictable seeds promote pre-dispersal specialists
31 BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Pre-Dispersal Specialization ! Granivores can be more selective when
seeds on plant ! Defenses in fruit have fewer constraints
than in seed ! Pre-dispersal granivores have impact on
potential for subsequent predator effects ! Increased seed defenses in specialist
relationship more likely to lead to granivore adaptation than switching
32
BIO 4134: Plant-Animal Interactions BIO 4134: Plant-Animal Interactions
Lodgepole Pine,
Squirrels and Crossbills
33
Fig. 5.12
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