Download Landscape Issues for Wildlife

Fragmentation, Edges, Reserves
and Connectivity
•Landscape perspective on wildlife
responses to vegetative change
•Edge Effects
–Nest predation
•Reserve Design and Theory
•Connectivity
Fragmentation or Habitat Loss?
• Habitat loss
can (or cannot)
increase
isolation of
remaining
patches and
increase (or
not) formation
of edges
• Fragmentation
creates edges
and reduces
patch size
Habitat Loss is Key Aspect of
Landscape Change
• Habitat loss may or may not
fragment
• To study fragmentation we
must focus on landscapes not
patches
• Few studies compare loss
and fragmentation
– All find loss most important
• Emphasizing fragmentation
rather than loss is
misleading, optimistic, and
distracts us from need to
conserve and restore habitat
(Fahrig 1999)
Lots of Ways to Measure
Landscape Pattern
• Amount of each class
– Critical probability at point of
percolation
• 50-65% of landscape depending
on pattern
• Aggregation of classes into patches
– Patch size, shape, P/A, edge, density
• Frequency distribution of patch
aggregation metrics
– Gives landscape its texture
• Spatial distribution of patches
– Distances between patches, exact
placement on landscape, distance to
important features.
(Hargis et al. 1997)
Fig 9.1 here
Thresholds in Response to
Habitat Loss are Likely
• Factors affecting how
much habitat is enough
– Greater demographic
potential
– Greater survival while
dispersing
• Less hostile matrix
– Patch occupancy
• Gap cross ability
• Habitat connectivity
• Area requirements
– Patch carrying capacity
(Fahrig 1999)
More habitat also
means more
connected habitat
(With 1999)
Conceptualizing
Breakup of
Habitat with
Increasing Loss
(Opdam and Wiens 2001)
Extinction probability drops when
50% of patches are occupied
(Vos et al. 2001)
Patch occupancy and extinction related
to fragmentation for nuthatches
(Opdam and Wiens 2001)
Patch occupancy not clearly related to neutral
landscape metrics
Fig4
Over
Fig 5
(Ecologically Scaled Landscape Indices Vos et al. 2001)
Seeing Landscapes from “Organism’s eye” clarifies
importance of amount and distribution of habitat
(Ecologically Scaled Landscape Indices Vos et al. 2001)
Case Study of Fragmentation
• In depth study links
reproduction, survival,
and dispersal to
fragmentation
– 7% of former habitat
left
– Lambda = 1.05 in
connected landscape,
but 0.94 in fragmented
• Due to increased
mortality during
dispersal, not
reproduction of survival
of adults
(Smith and Hellmann 2002)
Beauty is in the eye of the
beholder
• “Habitat” loss
and
fragmentation
actually
increases
resources
(habitat) for
other species
(Fahrig 1999)
A Bevy of Fragmentation Effects
Small Mammals
Clonal Plants
Other Plants
Deer
Mouse
Snakes
Small mammal persistence
(Robinson et al. 1992; 3 replicated treatments of 1 large, 6 med or 15 small grasslands)
NEST SUCCESS
Diversity
of Edge
Effects
DISTANCE FROM EDGE
(Murcia 1995)
Edge Effects Are Most Common
In Ag/Urban Landscapes
NUMBER OF STUDEIS
25
Significant Effect
Effect not Significant
20
P = 0.053
15
10
5
0
Ag/Urban
Forest
MATRIX HABITAT
(Marzluff and Restani 1999; also see Paton 1994 and Andren 1995)
Predator Identification Influences
Detection of Edge Effects
More Complete
PERCENTAGE OF
STUDIES
100%
Understanding
80%
60%
40%
20%
0%
Effect
No Effect
TYPE OF RESPONSE
No. I.D.
Corvids
Mammals
Corvids and Mammals
Predator Identification Influences
Detection of Fragmentation Effects
Better
PERCENTAGE OF
STUDIES
100%
Understanding
80%
60%
40%
20%
0%
Effect
No Effect
TYPE OF RESPONSE
No I.D.
Corvids
Mammals
Corvids and Mammals
We Need to Understand The
Behavior of the Predator
Habitat Selection Of Nest Predators
Matrix Habitat
Forest Habitat
Edge Specialist
Forest
Specialist
Matrix
Specialist
Forest
Generalist
Matrix
Generalist
• Habitat selection
– Predator and prey
– Matrix, edge, and/or
fragment
• Density and diversity
– Predator assemblage
– Alternative prey
• Behavior
– Searching behavior
– Defensive behavior
Learning how
Steller’s Jays forage
Vigallon and Marzluff (in press)
Incidental Predation
Correlates of s Can Indicate
Why Effects Are Not Greater
• Use of edges is
related to proximity
to human activity
(F(1,24) = 5.4; P=0.04)
Relative Use () of Edge
0.6
0.5
0.4
0.3
0.2
0.1
0.0
N = 10
N = 15
<1 Km
>5 Km
-0.1
-0.2
Proximity to Settled Areas and Campgrounds
– Anthropogenic food
available in these
settings
– Rate of predation on
other birds’ nests is
highest closest to
such edges in our
study area
Edge Effects into Reserves
• Carnivores with large
home ranges were
most sensitive to
reserve size because
they range outside of
reserve and are killed
(intentionally or
accidentally) by
people
(Woodroffe and Ginsberg 1998)
McArthur and Wilson’s Model
Colonization
small
large
Extinction
near
Rate
far
This drives concern for
size and connectivity
Number of Species
Lomolino’s (1999)View
• Insular distribution
functions
– Delineates combinations of
area and isolation where
extinction and immigration
rates are equal
• Focal species occur where
island characteristics
produce ratios with
extinction<immigration
and do not occur where
extinction>immigration
• Area determines extinction
(pop size)
• Isolation determines
Intercept measures minimum area requirement on mainland colonization
Slope measures inverse of immigration ability
Richness is not Linearly Related
to Area
• Driven by resources
requirements of
individual species
– Related to body size
– Skewed toward most
species needing few
resources
– As with most
relationships involving
body size, richness will
scale with area to the
~.26 power
Richness is not Linearly Related
to Isolation
• Threshold relationship
up to point where
isolation exceeds
immigration ability of
least vagile species
(Dnear)
– Related to individual
species’ immigration
abilities
• Distribution of slopes of
IDFs
– Most are limited
Resources, landscape, and community effects
What Does This Mean For
Reserves?
• Size and Isolation likely matter in non linear way
• Colonization is important, may be affected by “permeability”
of landscape
• Thresholds of occurrence of each species will occur
• Resources needs and presence of predators, competitors, etc
may affect final community composition
• Reserves may include nested subsets of entire fauna (those
with positive ratios of immigration to extinction)
Reserve study design factors
(Donnelly and Marzluff)
Small
Medium
Large
Increasing size
Exurban
Urbanization intensity
Suburban
Urban
Landscape designation based on
classified LANDSAT satellite image
• 3 Class
landcover
– Exurban
– Suburban
– Urban
• 29 Field sites
U
%%
U
U
%
U
%
U
%
U
%
U
%
U
%
U
%
U
%
U
%
U
%
U
%
U
%
U
%
U
%
%
U
U
U%
%
%
U
U
%
U
%
U
%
U
%
U
%
N
0
10 km
U
%
U
%
U
%
%
U
Richness was related to size and
landscape
• Landscape
• Size
– F = 19.1, P < 0.01
Mean richness + SE
– F = 4.3, P < 0.03
– Unexpected
direction consistent
with intermediate
disturbance?
30
25
Exurban
Suburban
Urban
20
15
10
5
0
Small Medium Large
Reserve size
• Detected more
species in larger
reserves because
– Detected more
individuals
– Increased chance
of detecting a
“new” species
Mean rarefied richness + SE
Controlling for sampling effort relegates size
to a qualifier for landscape effect
30
25
Interaction F = 4.9, P < 0.01
Exurban
Suburban
Urban
20
15
Size matters most in urban
10
5
0
Small Medium Large
Reserve size
Native forest species showed thresholds
of occurrence with size
• Matrix was
ordered
– % perfect
prediction =
19.2, P <
0.01
• Mean
threshold =
42 ± 15 ha
Synanthropic species showed thresholds of
occurrence with urban landcover
• Matrix was
ordered
– % perfect
prediction =
13.5, P < 0.02
• Mean threshold
= 40 ± 10 %
urban
landcover
Designing Reserve Complexes
•Enlarge key patches
•May require less total
reserved area than lots of small
patches
•Increase connectivity
(Opdam and Wiens 2002)
•Recognize patch dynamics
•Understand succession and
disturbance
•Reserves should be larger than
disturbance patch size
•Include internal recolonization
sources
•Include different ages of
disturbance-generated patches
(Pickett and Thompson 1978)
(Soulé 1991)
(Shafer 1997)
Do Corridors Provide Connectivity?
• Advantages
– Gene flow, rescue, recreates the normal condition of
species living in well-connected environments
• Disadvantages
– Spread disease, lure animals into poor habitat
• Beier and Noss (1998) review studies and
conclude that majority of well-designed ones show
benefits outweigh costs
– Need more B.A.C. studies that measure demography
– Need more observations of real dispersing animals in
real landscapes
• Cougars avoid urban barriers
• Argue that burden of proof should be on those
who will destroy the connections
Connectivity and Reserve Design
(Schmiegelow and Hannon 1999, Hannon and Schmiegelow 2002)
Long-term experimental study at
Calling Lake, Alberta
•1993-continuing, 3 replicates of patches of various
size and connectivity (100m-wide buffers)
•Species turnover is highest in small isolates,
indicating extinctions, but also colonizations.
•Richness remained equal among treatments
indicating replacements of permanent residents
on the small, isolated fragments
•Resident birds went extinct most frequently
•Species vary in their ability (“willingness”?)
to cross gaps, but this sensitivity does not
predict whether they will remain abundant in
connected fragments versus isolated ones
•Corridors may help a few resident species
(via rescue effects), but they do not appear to
offset the impacts of fragmentation (habitat
loss, edge creation) for most boreal birds
•May benefit western tanagers and blackthroated green warblers most
•May be better to use forest allocated to
corridors to actually increase size of reserves
instead of connecting small reserves
Manage the Vegetation in the
Fragment
• Maintain native
vegetation
• Increase foliage height
diversity
• Actively discourage
lawns
• Manage limiting
factors
– Small mammals
– Cats
– Exotic species
Manage the Matrix
• Regulate, enforce, educate to
reduce penetration of
predators, competitors,
humans, chemicals, etc. from
matrix into fragment
• Make the habitat in the
matrix more like habitat in
fragment
• Reduce food
supplementation
• Control cat movements
Design Creative Buffers
• Buffering with space
alone is not enough
• Buffers must reduce the
penetration of undesirable
agents from the matrix
into the fragment
– Harsh, sterile, unihabitable
habitats may be best!
– Good habitat may act as a
“wick” rather than a buffer
Recognize the Importance of
Distant Lands
• Populations in
fragments may be
supported by
dispersal from
distant “source”
populations
• Protect distant
sources by keeping
them DISTANT
– develop growth
management policies
Exurban
Suburban
Wildland
Urban
Realize That You Cannot Make Fragments
Suitable for All Species
• As the matrix becomes more
hostile, conservation of many
species will be difficult to
impossible
• Concentrate on the native
species that reproduce and
survive well.
• Identify and stop maintaining
“sink” populations
• Some fragments may not be
suitable as reserves at all
– Use as educational centers
Making Parks Successful
• Parks appear effective at
stopping land clearing and
stemming some threats to
biodiversity (Bruner et al. 2001)
– Degree of effectiveness correlates
with enforcement, boundary
demarcation, compensation of
locals
• But is this enough? (Stern 2001)
– Need constituency-building among
locals
– Otherwise costs of purchase pale in
comparison to costs of social
upheaval and conflict
• Community-based conservation
is needed in conjunction with
preservation
Reserves in Conservation
Planning Perspective
• Reserves are not enough
– Cornerstone that separates biodiversity from its threats
– Need to represent adequately biodiversity of a region
• Past planning has been opportunistic not systematic
– Science and social, economic, and political imperatives
need to meet and be compromised
• Design criteria of reserves has been discussed, now
need to see how the science of biogeography,
metapopulations, evolutionary significant units, and
source-sink dynamics, among others are modified to
result in on-the-ground reserves
(Margules and Pressey 2000)
Computational Methods Exist to
Guide Reserve Network Design
• Goal is to ID sets of reserves that maximize
biodiversity in a region (Cabeza and Moilanen 2001)
– With minimal sites, area, or cost
– Mathematical optimization problem
– Rarely used in practice
• More common is to take most vulnerable sites
first, then those representing species that are
irreplaceable (Margules and Pressey 2000)
• Regardless, the success of reserves at representing
biodiversity and then maintaining it for the longterm is rarely assessed
References
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