A rodent-dispersed tree species in a fragmented landscape: Seed and seedling survival addressed using experimental approaches
S. Chauvet, A. Leitao, A. Dalecky, P.-M. Forget
Biological context Fragmentation (sampling, isolation, and edge effects)
Biological context Fragmentation (sampling, isolation, and edge effects)
Rodent community
Biological context Fragmentation (sampling, isolation, and edge effects)
Rodent community
Plant populations
Biological context Fragmentation (sampling, isolation, and edge effects)
Rodent community
Plant populations
Resource community
Biological context Fragmentation (sampling, isolation, and edge effects)
Rodent community
Plant populations
Plant-rodent interactions (seed-seedling predation, and seed dispersal)
Resource community
Biological context Fragmentation (sampling, isolation, and edge effects)
Rodent community
Plant populations
Resource community
Plant-rodent interactions (seed-seedling predation, and seed dispersal)
⇒ Rodent-dispersed tree species are the more affected
Problematic 1- Early stages of regeneration in fragmented landscape ? ► Seed removal and dispersal rates ► Survival and establishment of dispersed seeds
Problematic 1- Early stages of regeneration in fragmented landscape ? ► Seed removal and dispersal rates ► Survival and establishment of dispersed seeds 2- Proximal factors underlying variation among forest patches ? ► Abundance of large rodents ► Tree population density ► Abundance and / or diversity of resources
Saint-Eugène (French Guiana)
Saint-Eugène (French Guiana)
Saint-Eugène (French Guiana)
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species ► Episodic and synchronized fruiting (mast-fruiting) ► Fruiting in April-June (peak of resources availability)
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species ► Episodic and synchronized fruiting ► Fruiting in April-June ► Large pods, with one heavy seed
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species ► Episodic and synchronized fruiting ► Fruiting in April-June ► Large pods, with one heavy seed
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species ► Episodic and synchronized fruiting ► Fruiting in April-June ► Large pods, with one heavy seed ► Seed predators: rodents, peccaries, beetle larvae ► Seed dispersal: scatter-hoarding rodents
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species ► Episodic and synchronized fruiting ► Fruiting in April-June ► Large pods, with one heavy seed ► Seed predators: rodents, peccaries, beetle larvae ► Seed dispersal: scatter-hoarding rodents
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species ► Episodic and synchronized fruiting ► Fruiting in April-June ► Large pods, with one heavy seed ► Seed predators: rodents, peccaries, beetle larvae ► Seed dispersal: scatter-hoarding rodents
Vouacapoua americana (Caesalpiniaceae) ► Canopy tree species ► Episodic and synchronized fruiting ► Fruiting in April-June ► Large pods, with one heavy seed ► Seed predators: rodents, peccaries, beetle larvae ► Seed dispersal: scatter-hoarding rodents ► Germination within few weeks
Study patches CF3 14 2
20
3
CF2 1 km
1 km
Patch characteristics 20
14
2
3
CF2
CF3
Area (ha)
7.5
7.9
28
67
–
–
V. americana a
6.4
5.9
4.2
4.6
0
7.4
D. leporina (ind./ km)
0.87
0.47
0.88
0.47
0.21
1.14
Fruit abundance
2766
4721
5718
3596
3948
3342
No. fruit species
31
49
22
30
33
39
a
Expressed in mean neighborhood size in a 50-m radius.
Patch characteristics 20
14
2
3
CF2
CF3
Area (ha)
7.5
7.9
28
67
–
–
V. americana a
6.4
5.9
4.2
4.6
0
7.4
D. leporina (ind./ km)
0.87
0.47
0.88
0.47
0.21
1.14
Fruit abundance
2766
4721
5718
3596
3948
3342
No. fruit species
31
49
22
30
33
39
a
Expressed in mean neighborhood size in a 50-m radius.
Patch characteristics 20
14
2
3
CF2
CF3
Area (ha)
7.5
7.9
28
67
–
–
V. americana a
6.4
5.9
4.2
4.6
0
7.4
D. leporina (ind./ km)
0.87
0.47
0.88
0.47
0.21
1.14
Fruit abundance
2766
4721
5718
3596
3948
3342
No. fruit species
31
49
22
30
33
39
a
Expressed in mean neighborhood size in a 50-m radius.
Patch characteristics 20
14
2
3
CF2
CF3
Area (ha)
7.5
7.9
28
67
–
–
V. americana a
6.4
5.9
4.2
4.6
0
7.4
D. leporina (ind./ km)
0.87
0.47
0.88
0.47
0.21
1.14
Fruit abundance
2766
4721
5718
3596
3948
3342
No. fruit species
31
49
22
30
33
39
a
Expressed in mean neighborhood size in a 50-m radius.
Seed fate experiments: methods 1
► During fruiting peak ► Thread-marked seeds ► Relocation within 10 m ► Recorded as intact, consumed or cached
Seed fate experiments: methods 2 1- Under parent trees: ► 10 trees / patch (5 patches) ► 1 seed set / tree ► 20 thread-marked seeds / seed set ► Control through end of May (3 weeks)
Seed fate experiments: methods 3 2- Away from parent trees: ► 200-m transect / patch (6 patches) ► 20 seed sets / transect ► 5 thread-marked seeds / seed set ► Control through end of May (2 weeks)
Seed fate experiments: results 1 1- Under parent trees:
Seed fate experiments: results 1 1- Under parent trees:
Intact
Consumed
Cached
% seeds
100 75 50 25 0
20
14
2
3
CF2 CF3
Seed fate experiments: results 1 1- Under parent trees: Anova: patch: ∗ Intact
Consumed
Cached
% seeds
100 75 50 25 0
20
14
2
3
CF2 CF3
Seed fate experiments: results 1 1- Under parent trees: Anova: patch: ∗ Intact
Consumed
Cached
% seeds
100
Correlations: Correlations
75
- V. a. density: ∗
50 25
- D. l. abundance: ns
0
- Fruit abundance: ns 20
14
2
3
CF2 CF3
- No. fruit species: ∗
Seed fate experiments: results 2 2- Away from parent trees:
Seed fate experiments: results 2 2- Away from parent trees:
Intact
Consumed
Cached
% seeds
100 75 50 25 0
20
14
2
3
CF2 CF3
Seed fate experiments: results 2 2- Away from parent trees: Anova: patch: ∗ Intact
Consumed
Cached
% seeds
100 75 50 25 0
20
14
2
3
CF2 CF3
Seed fate experiments: results 2 2- Away from parent trees: Anova: patch: ∗ Intact
Consumed
Cached
% seeds
100
Correlations: Correlations
75
- V. a. density: ∗
50 25
- D. l. abundance: ns
0
- Fruit abundance: ns 20
14
2
3
CF2 CF3
- No. fruit species: (∗)
Seed fate experiments: conclusions ► Low seed removal rates ⇒ predator satiation
Seed fate experiments: conclusions ► Low seed removal rates ⇒ predator satiation
► Similar results “under and away” + corr. coefficients ⇒ satiation at population + community levels
Seed fate experiments: conclusions ► Low seed removal rates ⇒ predator satiation
► Similar results “under and away” + corr. coefficients ⇒ satiation at population + community levels
► No opposition between CF and islands ⇒ no apparent effect of fragmentation after 4 years
Seedling experiment: methods ► Germinating seeds, planted below ground level ► Planted at the end of May ► Survival with or without protection with wire exclosure
Seedling experiment: methods ► Germinating seeds, planted below ground level ► Planted at the end of May ► Survival with or without protection with wire exclosure
Seedling experiment: methods ► Germinating seeds, planted below ground level ► Planted at the end of May ► Survival with or without protection with wire exclosure
► 200-m transect / patch (6 patches) ► 10 locations / transect ► 5 protected seeds + 5 unprotected seeds / location ► Census after 6 and 12 months
Seedling experiment: results Protected 100
Unprotected
6 mo
75
% seedlings
50 25 0 100
12 mo
75 50 25 0 20
14
2
3
CF2 CF3
Seedling experiment: results Protected 100
Overall survival: protection: ∗
6 mo
75
% seedlings
Unprotected
50
patch: ∗
25
protection x patch: ns
0 100
12 mo
75 50 25 0 20
14
2
3
CF2 CF3
Seedling experiment: results Protected 100
Overall survival: protection: ∗
6 mo
75
% seedlings
Unprotected
50
patch: ∗
25
protection x patch: ns
0 100
Mortality due to terrestrial
12 mo
75
mammals:
50 25
patch: ns
0 20
14
2
3
CF2 CF3
Seedling experiment: conclusions ► Mortality with vs. without protection ⇒ due to insects, pathogens and abiotic factors: 12-70% ⇒ due to terrestrial mammals: 0-30%
Seedling experiment: conclusions ► Mortality with vs. without protection ⇒ due to insects, pathogens and abiotic factors: 12-70% ⇒ due to terrestrial mammals: 0-30% ► Similar results after 6 and 12 months ⇒ seed-seedling mortality occurs early
Seedling experiment: conclusions ► Mortality with vs. without protection ⇒ due to insects, pathogens and abiotic factors: 12-70% ⇒ due to terrestrial mammals: 0-30% ► Similar results after 6 and 12 months ⇒ seed-seedling mortality occurs early ► Variability among patches ⇒ only for [insects + pathogens + abiotic factors]
General conclusions 1- Determinant steps in early regeneration: first months (or weeks) 2- Seed removal and dispersal by rodents: function of predator satiation (population- and community-levels)
General conclusions 1- Determinant steps in early regeneration: first months (or weeks) 2- Seed removal and dispersal by rodents: function of predator satiation (population- and community-levels)
Fragmentation, via reduction of tree population size, is likely to affect the mast-fruiting strategy of this species
General conclusions 1- Determinant steps in early regeneration: first months (or weeks) 2- Seed removal and dispersal by rodents: function of predator satiation (population- and community-levels)
Fragmentation, via reduction of tree population size, is likely to affect the mast-fruiting strategy of this species New selective pressures on early stages of regeneration
General conclusions 1- Determinant steps in early regeneration: first months (or weeks) 2- Seed removal and dispersal by rodents: function of predator satiation (population- and community-levels)
Fragmentation, via reduction of tree population size, is likely to affect the mast-fruiting strategy of this species New selective pressures on early stages of regeneration Consequences for dispersal process ?
