Population Ecology: BIOL708R, Spring 2013

Liabeth Yohannes

Motivation

Introduction

Results

Summary of key points

Conclusions

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

Motivation

Introduction

Results

Summary of key points

Conclusions

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