1020 ecologist at work bb
DESCRIPTION
BioTRANSCRIPT
" 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
" 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
" 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.
" 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
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
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