Population Ecology: BIOL708R, Spring 2013 Ecology Spring 2013... · “Population Structure of...
Transcript of Population Ecology: BIOL708R, Spring 2013 Ecology Spring 2013... · “Population Structure of...
What is the impact of human harvest on Brazil nut tree population regeneration and fruit production?
Bertholletia excelsa is among the most valuable NTFP
Worth $US 10 million annually in Brazil
100,000’s of people involved in harvest,
invested in BN forests
IUCN - Vulnerable
Native to Brazil, Bolivia, Ecuador, Guyana, Colombia, Peru
Thought to exist only in mature forest, but cultivated areas too!
Low densities ~ 1-20 trees / ha (> 10 cm dbh), Stands of 50-100 trees
Max size: 50 m tall, 3 m dbh!
Kainer et al. 1999
Motivation
Introduction: Factors affecting reproduction, dispersal, and
population growth
Results
Summary of key points
Conclusions
Need high light Repro. size > 40 dbh cm Repro. age > 120 yrs
For large trees:
Good crown
form and low liana
load important for fruit production
Sources: Zuidema and Boot 2002; Wadt et al. 2005
Triangle = Dawkins crown illumination index Circle = Reproductive status Line = Log. regression for repro. status
Annual fruit production: Only ¼ trees account for ¾ fruit production
Energetic tradeoff
Per tree:
▪ 100 – 150 fruits
▪ 10 – 21 nuts per fruit
▪ 5 lbs per fruit, up to 250 lbs per year
High prod. at 80-160 cm dbh
Sources: Kaiser et al. 2007; Zuidema and Boot 2002; Wadt et al. 2005
Dispersed by agouti scatter-hoarders
Transport 25 – 100 m
Pollinated by large-bodied bees, Euglossa spp.
What vital statistics most affect population growth?
Individual growth vs. fecundity vs. survivorship
Methods: Elasticity analysis for population projection
matrix of 2 BN populations under high harvest (93%)
Zuidema and Boot 2002
Pop growth is most sensitive to survivorship, less sensitive to growth and reproduction
Suggests fruit harvest has low impact on growth, maintenance of pop
Square = stasis elements Triangle = growth Dark circles = fecundity Zuidema and Boot 2002
Dilemma:
Long time to detect changes in fruit production and regeneration due to harvest because…..
Age of first reproduction
~ 120+ yrs
Long-lived
Largest individuals > 160 cm dbh, Age > 350 yrs
High survivorship
~ no mortality for > 1 cm dbh
Motivation
Introduction Results: Impact of human harvest on BN
populations Negative vs. positive or no impact
Summary of key points
Conclusion
Method: Compared impact of harvest intensity on 23 BN populations in LA Results: High harvest intensity
Low % juveniles Greater dbh Lower s* parameter
Low s* parameter High median dbh Sigmoidal size distributions
▪ Few small, high large sizes
Peres et al. 2003
Method: Projected pop. structure over 200 years of intense harvest (used Lefkovitch) Results: High harvest intensity =
Increased median size (low s1)
Low size variation (high s2)
Pops under intensive long-term harvest will succumb to demographic collapse?
Oversimplification of model? Removed potential explanatory variables: Longitude, large herbivore & agouti abundance, total
rainfall significantly correlated with % juveniles
No replicability?
Methods: Compared pop. structure between sites with
different land use histories in N. Brazil Results: Low human activity Lower regeneration
High human activity Higher regeneration
Higher tree density, crown
Scoles and Gribel 2011 Note: Trompetas (low) = dark lines, Capana (high) = white lines
Methods: Compared fruit production, regeneration at 3 sites of varying harvest intensity Results: High harvest levels (F., P.)
High % juveniles, low fruit production
Low harvest levels (C.) Low % juveniles, high fruit production
Low juveniles – high fruit production?
C. had high basal area (less light) Drier climate, fewer lianas
High Low High harvest levels
Methods: Compared BN tree
density with past ag. use Results: Shifting cultivation
positively correlated with BN density
Factors such as light, age, size, crown form and liana crown load are important for BN population growth and fruit production
For now, human harvest has a positive or neutral impact on pop growth
Compatible with other livelihoods, promotes
forest conservation
Brazil nut harvest important to tropical forest conservation
Policies restricting
harvest not warranted
More research needed about long-term impacts
Questions?
Duvall, John N. "The (Super)Marketplace of Images: Television as Unmediated Mediation in
DeLillo's White Noise." Arizona Quarterly 50.3 (1994): 127-53. Print.
Paiva, Paulo, M. Guedes, C. Funi. “Brazil nut conservation through shifting cultivation.” Forest Ecology and Management. 261 (2011) 508–514. Print.
Peres, Carlos, A., C. Baider, P. Zuidema, L. Wadt, K. Kainer, et al. Demographic Threats to the Sustainability of Brazil Nut Exploitation. Science 302. 5653 (2003): 2112-2114. Print.
Scoles, Ricardo, R. Gribel. “Population Structure of Brazil Nut (Bertholletia excelsa, Lecythidaceae) Stands in Two Areas with Different Occupation Histories in the Brazilian Amazon.” Human Ecology 39 (2011): 455–464. Print.
Wadt, Lucia, H.O., K. Kainer, D. Gomes-Silva. “Population structure and nut yield of a Bertholletia excelsa stand in Southwestern Amazonia.” Forest Ecology and Management 211 (2005) 371–384. Print.
Zuidema, Pieter, A., R. Boot. “Demography of the Brazil Nut Tree (Bertholletia excelsa) in the Bolivian Amazon: Impact of Seed Extraction on Recruitment and Population Dynamics.” Journal of Tropical Ecology 18.1 (2002): 1-31. Print