Download Habitat use, selection and preference

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Habitat Use,
Selection and
Preference
ESRM 450
Wildlife Ecology and
Conservation
Habitat
any area offering the resources and
conditions that promote occupancy by
a species
Hall et al. (1997) Wildlife Society Bulletin
any area offering the resources and
conditions that promote occupancy by a
species
•  Definition
–  transcends floristic composition; resources include food, cover,
shelter, other factors influencing occupancy
–  species-specific
–  scale-dependent
•  e.g., a forest may be habitat for a flying squirrel, but at a finer
spatial scale certain trees may not
–  has temporal component (e.g., resources can wax and wane)
Hall et al. (1997) Wildlife Society Bulletin
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any area offering the resources and
conditions that promote occupancy by a
species
•  Definition
–  transcends floristic composition; resources include food, cover,
shelter, other factors influencing occupancy
–  species-specific
–  scale-dependent
•  e.g., a forest may be habitat for a flying squirrel, but at a finer
spatial scale certain trees may not
–  has temporal component (e.g., resources can wax and wane)
•  Means that habitat is not always wilderness
–  Human activity can both create and destroy habitat (e.g.,
cottontail rabbits and jackrabbits)
Hall et al. (1997) Wildlife Society Bulletin
Cottontails and Jackrabbits
•  Conversion of open rangeland
to farmland has created habitat
for eastern cottontail rabbits
(Sylvilagus floridanus)
–  utilize hedgerows, gardens
–  seek cover along fences
•  But has constricted white-tailed
jackrabbit (Lepus townsendii)
habitat
–  depend on the open prairie
any area offering the resources and
conditions that promote occupancy by a
species
•  Definition provides basis for explaining why animals are
in some areas, not others
-  An area provides the necessary resources and conditions for a
species or does not
Hall et al. (1997) Wildlife Society Bulletin
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Habitat Quality
•  Habitats vary in quality
•  Quality: degree to which habitat promotes individual
fitness, and by extension population growth
–  continuous variable
–  linked to demography, not density or vegetative characteristics
–  Why not density?
Hall et al. (1997) Wildlife Society Bulletin
Habitat Quality
•  Habitats vary in quality
•  Quality: degree to which habitat promotes individual
fitness, and by extension population growth
–  continuous variable
–  linked to demography, not density or vegetative characteristics
–  Why not density? Animals can congregate in, or be forced into,
areas where they fare poorly
Hall et al. (1997) Wildlife Society Bulletin
Habitat Quality
•  Habitats vary in quality
•  Quality: degree to which habitat promotes individual
fitness, and by extension population growth
–  continuous variable
–  linked to demography, not density or vegetative characteristics
–  Why not density? Animals can congregate in, or be forced into,
areas where they fare poorly
–  Why not vegetative characteristics?
Hall et al. (1997) Wildlife Society Bulletin
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Habitat Quality
•  Habitats vary in quality
•  Quality: degree to which habitat promotes individual
fitness, and by extension population growth
–  continuous variable
–  linked to demography, not density or vegetative characteristics
–  Why not density? Animals can congregate in, or be forced into,
areas where they fare poorly
–  Why not vegetative characteristics? Remember, a particular
plant association may promote high fitness in one animal
species but not another
Hall et al. (1997) Wildlife Society Bulletin
Habitat Use
The way an animal uses the collection
of conditions and resources in a habitat
Hall et al. (1997) Wildlife Society Bulletin
Habitat Use
•  Typically measured as relative amount of time spent in
different areas within habitat
–  More time in certain area means more use of resources or
conditions at that location
–  Can be measured for individuals, populations
•  Patterns of habitat use can vary with behavior
–  foraging, denning, hiding, resting
–  behavior-specific habitat use patterns often specified (e.g.,
foraging habitat use )
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Habitat Use
•  Habitat use is also
–  Scale-dependent
•  a forest might be used at a large scale, but certain parts of a forest
won t be used at a finer scale (when we zoom in)
–  Subject to temporal variability
•  e.g., patterns of habitat use can change seasonally
Foraging Dugong Habitat Use
Dugong (Dugong dugon)
Deep channels (> 6 m in depth)
Shallow water (< 4.5 m in depth)
Pattern is temporally variable
Wirsing et al. (2007) Oecologia
Habitat Use
Are habitat use patterns necessarily a
reflection of choice?
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Habitat Use
•  No, because they are realized
•  e.g., observed patterns of habitat use may be driven
entirely by
–  Predation (spatial and temporal patterns of mortality)
–  Competition (exclusion; e.g., blue mussels Mytilus edulis)
–  These forces are external constraints
Habitat Use
But, habitat use patterns can reveal
resources and conditions that are important
drivers of fitness, and by extension
distributions and population dynamics
Studying Habitat Use
•  Explaining habitat use is a cornerstone of wildlife
ecology
–  but how do we identify the resources and conditions that affect
habitat use?
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Studying Habitat Use
•  Explaining habitat use is a cornerstone of wildlife
ecology
–  but how do we identify the resources and conditions that affect
habitat use?
•  Two approaches
(1)  Experimental (manipulative): alter factors that may be
influential (perturbation may be temporal and/or spatial; lab or
field-based)
(2)  Observational (mensurative): relate use to natural variation in
factors that may be influential (temporal and/or spatial)
Why are most habitat use studies observational?
Use-Only Approaches
•  Resource Utilization Functions (RUF): observational
approach to understanding animal habitat use, typically
within the home range
•  Step 1: obtain raw locations
-  e.g., via observation, telemetry
Kertson and Marzluff (2010) Environmental Conservation
Step 2: Convert Raw Points to
Utilization Distribution (UD)
•  UD: Probability density
function (pdf) quantifying
time allocation, or
concentration of use,
within home range
–  Sums to 1
–  3D, use = height (volume)
of UD
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Animal
relocations
Ruf.fit
(multiple
regression)
Utilization Distribution
Sampling grid
Use and habitat covariates
The Final Step: A RUF
RUFs: multiple regression equations that relate intensity of
use to resources in a specified area, typically within
an animal s home range
- coefficient estimates not overlapping zero indicate influential
resources
Habitat Selection
The process, both innate and learned,
by which animals choose which habitat
components (conditions, resources) to
use
Hall et al. (1997) Wildlife Society Bulletin
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Habitat Selection
•  To really know what an animal is choosing, we would
have to understand its decision-making process
-  all but impossible in most cases
•  So, we use indicators of choice to infer selection of
particular conditions and resources
•  One popular indicator: use relative to availability
-  Overuse = selection; underuse = avoidance
-  Some techniques: randomization, resource selection functions
(RSFs)
-  Challenge: determining what is available
Habitat Selection by Tiger Sharks
Use (observed – expected)
0.1
Selected
0.08
0.06
0.04
0.02
No Pattern
0
-0.02
-0.04
-0.06
-0.08
Shallow Banks
Deeper Waters
*Availability determined using randomization of shark tracks
Avoided
Heithaus et al. (2002) Marine Biology
Selected: used to degree
exceeding availability
Avoided: used less than
expected from availability
Resources
Telemetry (red),
Random (yellow)
points
Warton and Aarts (2013) J Anim Ecol
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avoided
Amur leopard
(Panthera pardus orientalis)
Selected (big surprise!)
Hebblewhite et al. (2011) Biological Conservation
Predicting Potential Habitat
Associated with
avoided resources
Associated with
selected resources
Hebblewhite et al. (2011) Biological Conservation
Habitat Preference
Selection of one habitat component
over another when both are equally
available
•  Hard to demonstrate without cafeteria-style experiments
–  So we stick with use and selection to be safe
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Habitat Use/Selection and
Conservation
•  Understanding of habitat use/selection facilitates
effective management, conservation
–  Identify habitats used intensely by the species of interest…and
those that seem to be avoided (selection)
–  Manage for habitats used/selected for specific activities (e.g.,
foraging, reproduction, denning)
–  Most importantly, if we understand mechanisms underlying use/
selection, we can predict how anthropogenic changes to
landscape are likely to affect animal distributions, populations
A Caveat
•  Management based on habitat use/selection snapshots
can be problematic
–  Observed pattern could be anomalous
–  Doesn t allow us to say much about how animal distributions
might change following landscape alteration (e.g., as a result of
human disturbance)
Five Minute Paper
Questions & Insights
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