Population Ecology: BIOL708R, Spring Liabeth Yohannes

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1 Population Ecology: BIOL708R, Spring 2013 Liabeth Yohannes

2 Motivation Introduction Results Summary of key points Conclusions

3 What is the impact of human harvest on Brazil nut tree population regeneration and fruit production?

4 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

5 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 trees Max size: 50 m tall, 3 m dbh! Kainer et al. 1999

6 Motivation Introduction: Factors affecting reproduction, dispersal, and population growth Results Summary of key points Conclusions

7 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 Triangle = Dawkins crown illumination index Circle = Reproductive status Line = Log. regression for repro. status Sources: Zuidema and Boot 2002; Wadt et al. 2005

8 Annual fruit production: Only ¼ trees account for ¾ fruit production Energetic tradeoff Per tree: fruits nuts per fruit 5 lbs per fruit, up to 250 lbs per year High prod. at cm dbh Sources: Kaiser et al. 2007; Zuidema and Boot 2002; Wadt et al. 2005

9 Dispersed by agouti scatter-hoarders Transport m Pollinated by large-bodied bees, Euglossa spp.

10 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

11 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

12 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

13 Motivation Introduction Results: Impact of human harvest on BN populations Negative vs. positive or no impact Summary of key points Conclusion

14 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

15 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)

16 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?

17 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 Note: Trompetas (low) = dark lines, Capana (high) = white lines Scoles and Gribel 2011

18 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

19 Methods: Compared BN tree density with past ag. use Results: Shifting cultivation positively correlated with BN density

20 Motivation Introduction Results Summary of key points Conclusions

21 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

22 Brazil nut harvest important to tropical forest conservation Policies restricting harvest not warranted Questions? More research needed about long-term impacts

23 Duvall, John N. "The (Super)Marketplace of Images: Television as Unmediated Mediation in DeLillo's White Noise." Arizona Quarterly 50.3 (1994): Print. Paiva, Paulo, M. Guedes, C. Funi. Brazil nut conservation through shifting cultivation. Forest Ecology and Management. 261 (2011) Print. Peres, Carlos, A., C. Baider, P. Zuidema, L. Wadt, K. Kainer, et al. Demographic Threats to the Sustainability of Brazil Nut Exploitation. Science (2003): 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): 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) 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): Print

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Rainforests and Tropical Diversity Gaby Orihuela Visitor Experience Manager Global Strategy for Plant Conservation Objective IV: Education and awareness about plant diversity, its role in sustainable livelihoods