Correlations between functional traits, environmental gradients, and distributional patterns of vascular epiphytes within tropical canopies in Costa Rica Carrie L. Woods, Ph.D candidate Clemson University ATBC 2013 1
Diversity Introduction Methods Results Conclusion • A central question in community ecology concerns the number of species able to coexist at small spatial scales ( a diversity) • High in tropical forests 2 Valencia et al. 1994, Woods et al. in prep
Diversity Introduction Methods Results Conclusion • Habitat heterogeneity promotes species diversity • Structurally complex environments enable habitat partitioning “Heterogeneity matters”, Deborah Clark, ATBC 2013 (Hutchinson 1959, MacArthur 1958, MacArthur and MacArthur 1961, Ricklefs 1977, Huston 1979, Tilman 1986, Rosenzweig 1995) 3
Functional traits Introduction Methods Results Conclusion • Relates the function of a plant to the environment – Resource allocation – Trade offs – e.g. leaf thickness • Enables a better prediction and understanding of the distribution and coexistence of species Westoby et al. 2002, Wright et al. 2004 4
Questions Introduction Methods Results Conclusion • Do epiphytes partition the canopy along habitat and resource gradients? • Do functional leaf traits explain the distribution of epiphytes within tree canopies? 5
Habitat diversity in the canopy • Structurally Habitat diversity complex temperature, • Habitat gradients wind RH Branch diameter (temperature, RH wind speed, branch Resource diversity diameter) • Resource gradients Light (canopy soil, Canopy soil atmosphere, light) Atmosphere (Parker 1995, Nadkarni 2004) 6
Vascular epiphytes: Functional complexity Introduction Methods Results Conclusion Water from tanks Atmospheric uptake Canopy soil Aerial roots Soil ferns Aroids, Orchids Tank bromeliads Atmospheric bromeliads Bark Ferns? • Multiple adaptations to take up water and nutrients 7
Vascular epiphytes: Functional complexity Introduction Methods Results Conclusion 8
Habitat partitioning of canopy by epiphytes Introduction Methods Results Conclusion • Habitat partitioning – Pittendrigh 1948 – Benzing and Renfrow 1971 – Johansson 1974 – Hietz and Briones 1998 – Zotz et al 2007 – Reyes-García 2012 • Habitat specialization? 9
Field site Introduction Methods Results Conclusion • La Selva Biological Research Station in Costa Rica • Wet tropical forest • 4000 mm of annual precipitation • Average monthly temperature is 25.8°C ± 0.2, and varies little throughout the year 10
Data collection methods Introduction Methods Results Conclusion • 5 emergent Virola koschnyi trees – 90° branches and no trunk epiphytes • Spatial distribution of epiphytes every meter (m) 11
Data collection methods Introduction Methods Results Conclusion • Habitat gradients – T, RH, vapor pressure deficit (VPD) – Branch diameter T/RH datalogger • Resource gradients – % canopy openness (light) – % canopy soil cover 12
Canopy zones: Inner (0-2 m) Introduction Methods Results Conclusion Inner canopy 0-2 m from trunk 13
Canopy zones: Mid (2-5 m) Introduction Methods Results Conclusion Mid canopy 2-5 m from the trunk 14
Canopy zones: Outer (> 5 m) Introduction Methods Results Conclusion Outer canopy > 5 m from the trunk 15
Habitat associations Introduction Methods Results Conclusion • Conservative randomization tests for epiphyte species associations for each canopy zone • Compared the Obs RelDen of each species to the Exp RelDen generated by 1000 iterations of random shuffling the 3 canopy zones (two tailed test, a = 0.05) • Obs > Exp 97.5% = positive • Obs < Exp 97.5% = negative 16 DeWalt et al. 2006
Functional leaf traits Introduction Methods Results Conclusion • Functional leaf traits of abundant epiphyte species within Virola koschnyi trees – 10 individual leaves per species – No orchids or atmospheric bromeliads – Soil ferns, Aroids, Tank bromeliads, and Bark ferns • Examined relationships between habitat and resource gradients and functional leaf traits 17
Functional leaf traits Introduction Methods Results Conclusion • Environmental conditions – Air VPD – Substrate temperature – % canopy openness • Functional leaf traits T/RH datalogger – Specific leaf area (SLA) – Leaf dry matter content (LDMC) – Succulence – Sclerophylly – Leaf toughness (LTo) – Rate of epidermal water loss (EWL) Leaf penetrometer 18
Habitat and Resource gradients: canopy zones Introduction Methods Results Conclusion 100 30 a a Branch diameter (cm) % canopy soil cover 25 80 20 60 b 15 b 40 10 c 20 5 Are different species associated with these diverse habitats? c 0 0 Inner (0-2 m) Mid (2-5 m) Outer (> 5 m) Inner (0-2 m) Mid (2-5 m) Outer (> 5 m) 3.0 b 60 c ab 2.5 a % canopy openness 50 2.0 VPD (kPa) b 40 1.5 30 a 1.0 20 10 0.5 0 0.0 Inner (0-2 m) Mid (2-5 m) Outer (> 5 m) 19 Inner (0-2 m) Mid (2-5 m) Outer (> 5 m) Woods et al. in prep
Habitat partitioning of canopy zones Introduction Methods Results Conclusion Inner + Mid Outer Atmospheric Bark ferns Soil ferns Aroids bromeliads All zones Low VPD, low % CO, soil Tank Orchids 20 bromeliads Woods et al. in prep
Habitat partitioning of canopy zones Introduction Methods Results Conclusion Inner + Mid Outer Atmospheric Bark ferns Soil ferns Aroids bromeliads All zones Low VPD, low % CO, soil High VPD, high % CO, bark Tank Orchids 21 bromeliads Woods et al. in prep
Habitat partitioning of canopy zones Introduction Methods Results Conclusion Inner + Mid Outer What mechanisms underlie this pattern? Atmospheric Bark ferns Soil ferns Aroids bromeliads All zones Low VPD, low % CO, soil High VPD, high % CO, bark Tank Orchids 22 bromeliads Woods et al. in prep
Trait-Environment Relationships Introduction Methods Results Conclusion 4 substrate temperature 2 air temperature Soil ferns CO VPD PCA2 (23.0%) Aroids 0 PCA2 RH Tank bromeliads -2 Bark ferns -4 (B) -4 -2 0 2 4 PCA1 PCA1 (39.9%) SLA 23
Functional leaf traits of functional groups Introduction Methods Results Conclusion 20 240 b a Sclerophylly (g m -2 ) b SLA (mm 2 mg -1 ) 200 16 a 12 160 a 120 8 a b 80 4 b 40 0 700 350 a b Succulence (g mm -2 ) LDMC (mg g -1 ) 300 600 250 500 b a a 200 c 400 a c 150 300 100 Soil fern Tank bromeliad Aroid Bark fern Soil fern Tank bromeliad Aroid Bark fern 24
Habitat partitioning based on functional traits Introduction Methods Results Conclusion Soil ferns and aroids Bark ferns Bark fern – shady sites with high RH and low VPD Tank bromeliads Tank bromeliad – Large investment in Aroids Aroid leaf structure Soil fern Soil ferns (A) Most tank bromeliads -4 -2 0 2 4 PCA1 and bark ferns PCA1 SLA – More open and hot Sclerophylly LDMC sites with high VPD Leaf thickness Succulence – Low investment in leaf structure 25
Functional strategies explain partitioning Introduction Methods Results Conclusion • Specialization to particular habitats based on functional leaf traits (niche partitioning) • Different species and functional groups converged on a similar strategy when in a similar habitat • Functional leaf traits explained the distribution of epiphytes within tree canopies 26
Acknowledgements Dr. Catherine Cardelús Rigoberto Vargas Carly Phillips Lindsay Martin Ralph Garcia, Minor Hidalgo, Angie Amesquita (REU), Sarah Callan, and Dr. Saara J. DeWalt (advisor) 27
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