" Two studies

" An observational study

! Why do female caribou have antlers?

" A field experiment

! What are the effects of hydroelectricdevelopment on migratory caribou?

Ecologist at Work

Caribou and reindeer

One species, Rangifer tarandus

W.R. Darby

Caribou and reindeer

A species in decline

Vors & Boyce (2009) Global Change Biology 15: 2626-2633

" A feature of the family Cervidae

" Deciduous, branched, entirely ofbone when fully developed! Originate from pedicel of frontal

bone! When growing, covered in

velvet.

What are antlers?

“The heavy energetic costs of annualantler renewal ... indicate that if antlersdid not afford their possessors someimportant advantage, selection wouldquickly suppress them.”

Functions of antlers?

A fascinating evolutionary problem

Clutton-Brock (1982) Behaviour 79:108

Functions of antlers?

! Males – used in intraspecific combat

" Monopolize matings with females

" Caribou females possess antlers! Unique among deer species

" Propensity of females to carry antlersvaries among caribou populations ! A polymorphic trait

Functions of antlers on females?

Caribou are a useful test case

" Female defense hypothesis! Defend against predators

" Andromimicry hypothesis! Mimic their young male offspring –

less likely to be ejected from groupby dominant males

" Resource defense hypothesis! Defend food from conspecifics.

Function of horn-like organs on female ungulates

Tentative explanations

" Aggressive displacements at feeding sites by caribou

! Snow-free: 0.3/animal/h

! Snowcover: 2.2/animal/h

Interference competition

Barrette & Vandal (1986) Behaviour 97:118-146

A prediction

" Resource defense hypothesis

! Proportion of female caribou with antlers will be positivelycorrelated to snow depth and duration.

An observational study

15 caribou herds in Newfoundland & Labrador

" Population density and sex structure, 1957-1996

! Percentage of females with antlers, October to April

" Climatic normals, 1960-1990

! Total annual snow fall

! Months with >25 cm snowcover

! Snow depth at the end of March.

The data

From field observations and climate records

Schaefer & Mahoney (2001) Ecology 12:3556

Dealing with potentially confounding variables

Variable A Variable Bis correlated with

Variable C

An issue in observational studies

Dealing with potentially confounding variables

Antlers Snowis correlated with

Populationdensity

An issue in observational studies

Dealing with potentially confounding variables

Control for them statistically

Schaefer & Mahoney (2001) Ecology 12:3556

" Female defense hypothesis

! Calf hiding behaviour is notuncommon

" Andromimicry hypothesis

! Females retain their antlers longerthan young males.

Rival hypotheses

Antlers on female caribou

“The most convincing evidence offemale weaponry being used incontest for limited feeding sites”

Roberts (1996) Behaviour 133:399

Caribou and reindeer

A species in decline

Vors & Boyce (2009) Global Change Biology 15: 2626-2633

Effects of hydroelectric development?

Effects of hydroelectric development?

Extent of avoidance of human-caused disturbances

A field experiment

Buchans caribou herd and the Star Lake development

Newfoundland

0 25 km

Buchans caribouBU 1043

Star Lake

" 15 mW powerhouse! 18 m high dam! 45 km transmission

line! 9.3 km2 flooding

" Construction! May 1997 to

September 1998

" The project = anexperiment

" Hypothesis

! Such industrial projects cause functional lossof habitat, well beyond its strict bounds

" Prediction

! During construction, migration will bedisrupted

! During and after construction, caribou willexhibit reduced use of the project vicinity.

Hypothesis and predictions

Rank order of migration

Consistent year-to-year

Mahoney & Schaefer (2002) Biological Conservation 107:147

Rank order of migration

Temporarily disrupted during construction

Duringconstruction

Mahoney & Schaefer (2002) Biological Conservation 107:147

Avoidance of the development

" 50% habitat loss atleast 3 km fromproject

Mahoney & Schaefer (2002) Biological Conservation 107:147

Effects of hydroelectric development?

Extent of avoidance of human-caused disturbances

Adaptive management

Treat each industrial development as an experiment

Plan & do

Evaluate & adjust