Fragmentation, Edges, Reserves and Connectivity

1
Fragmentation, Edges, Reserves and Connectivity

• Landscape perspective on wildlife responses to
  vegetative change
• Edge Effects
• Nest predation
• Reserve Design and Theory
• Connectivity

2
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

3
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)
4
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.

Fig 9.1 here
(Hargis et al. 1997)
5
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)
6
More habitat also means more connected habitat
(With 1999)
7
Conceptualizing Breakup of Habitat with
Increasing Loss
(Opdam and Wiens 2001)
8
Extinction probability drops when 50 of patches
are occupied
(Vos et al. 2001)
9
Patch occupancy and extinction related to
fragmentation for nuthatches
(Opdam and Wiens 2001)
10
Patch occupancy not clearly related to neutral
landscape metrics
Fig4 Over Fig 5
(Ecologically Scaled Landscape Indices Vos et
al. 2001)
11
Seeing Landscapes from Organisms eye clarifies
importance of amount and distribution of habitat
(Ecologically Scaled Landscape Indices Vos et
al. 2001)
12
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)
13
Beauty is in the eye of the beholder

• Habitat loss and fragmentation actually
  increases resources (habitat) for other species

(Fahrig 1999)
14
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)
15
Diversity of Edge Effects
(Murcia 1995)
16
Edge Effects Are Most Common In Ag/Urban
Landscapes
P 0.053
(Marzluff and Restani 1999 also see Paton 1994
and Andren 1995)
17
Predator Identification Influences Detection of
Edge Effects
More Complete Understanding
18
Predator Identification Influences Detection of
Fragmentation Effects
Better Understanding
19
We Need to Understand The Behavior of the Predator

• Habitat selection
• Predator and prey
• Matrix, edge, and/or fragment
• Density and diversity
• Predator assemblage
• Alternative prey
• Behavior
• Searching behavior
• Defensive behavior

20
Learning how Stellers Jays forage Vigallon and
Marzluff (in press)
21
Incidental Predation
22
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 P0.04)
• Anthropogenic food available in these settings
• Rate of predation on other birds nests is
  highest closest to such edges in our study area

23
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)
24
McArthur and Wilsons Model
small
large
Colonization
Extinction
near
Rate
far
This drives concern for size and connectivity
Number of Species
25
Lomolinos (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 extinctionltimmigration and do
  not occur where extinctiongtimmigration
• Area determines extinction (pop size)
• Isolation determines colonization

Intercept measures minimum area requirement on
mainland Slope measures inverse of immigration
ability
26
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

27
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

28
Resources, landscape, and community effects
29
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)

30
Reserve study design factors(Donnelly and
Marzluff)
Medium
Small
Large
Increasing size
Suburban
Exurban
Urban
Urbanization intensity
31
Landscape designation based on classified LANDSAT
satellite image

• 3 Class landcover
• Exurban
• Suburban
• Urban
• 29 Field sites

N
0
10 km
32
Richness was related to size and landscape

• Landscape
• F 4.3, P lt 0.03
• Unexpected direction consistent with intermediate
  disturbance?
• Size
• F 19.1, P lt 0.01

33
Controlling for sampling effort relegates size to
a qualifier for landscape effect

• Detected more species in larger reserves because
• Detected more individuals
• Increased chance of detecting a new species

Interaction F 4.9, P lt 0.01
Size matters most in urban
34
Native forest species showed thresholds of
occurrence with size

• Matrix was ordered
• perfect prediction 19.2, P lt 0.01
• Mean threshold 42 15 ha

35
Synanthropic species showed thresholds of
occurrence with urban landcover

• Matrix was ordered
• perfect prediction 13.5, P lt 0.02
• Mean threshold 40 10 urban landcover

36
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)

37
(Soulé 1991)
(Shafer 1997)
38
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

39
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 black-throated
  green warblers most
• May be better to use forest allocated to
  corridors to actually increase size of reserves
  instead of connecting small reserves

40
Manage the Vegetation in the Fragment

• Maintain native vegetation
• Increase foliage height diversity
• Actively discourage lawns
• Manage limiting factors
• Small mammals
• Cats
• Exotic species

41
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

42
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

43
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
44
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

45
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

46
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

47
(Margules and Pressey 2000)
48
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 long-term is rarely assessed

49
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