Spatial Graphs for Assessing Woodland Caribou Habitat Connectivity Dan O’Brien, MSc, RPBio (Cortex Consultants Inc.) Micheline Manseau, PhD (Parks Canada)

Spatial Graphs for Assessing Woodland

Caribou Habitat ConnectivityDan O’Brien, MSc, RPBio

(Cortex Consultants Inc.)

Micheline Manseau, PhD(Parks Canada)

Andrew Fall, PhD(Gowlland Technologies Ltd.)

Marie-Josée Fortin, PhD(Dept. Zoology, University of Toronto)

Chase Habitat Supply Modelling Workshop

November 23 – 25, 2004

Chase Habitat Modelling Workshop Nov 2004 Dan O’Brien

Presentation Outline

Using spatial graphs to measure structural connectivity of a landscape

Application

An assessment of Woodland caribou (Rangifer tarandus caribou) habitat connectivity in Manitoba

Methods for detecting an association between distribution of caribou and the structural connectivity of their range


Habitat Connectivity

Connectivity is the degree to which landscape facilitates or impedes dispersal among resource patches (Taylor et al. 1993)

Structural connectivity

linkage of resource patches by physical adjacency

Functional connectivity

linkage of resource patches by processes that depend on dispersal and movement behaviour of the species


Habitat Connectivity

Approaches to analyzing connectivity fall on a continuum

STRUCTURAL FUNCTIONAL

SPATIAL GRAPHS INDIVIDUAL BASED DISPERSAL MODELS

INTRA-PATCH METRICS

e.g., patch cohesion

INTERPATCH METRICS

e.g., nearest neighbour distance


Spatial Graphs for measuring landscape connectivity

Nearest Neighbor links

Shortest links connecting patches, such that each patch forms at least one link



Minimum Spanning Tree

The minimum set of links such that each patch is connected into a single component

There can be no other link with greater length linked to a patch

“Backbone” of connectivity



Minimum Planar Graph (MPG)

At least one link between each pair of patches,

No link can cross any another link

All links are shortest path between pairs of patches



The MPG is a Triangulation of Patches

Linked patches form a Delauney Triangulation

The dual is the Voronoi surface

Voronoi boundaries are equidistant from all patches

Each point in Voronoi polygon is closest to the interior patch than any other


Forming links along a cost surface

Patches are linked along the least-cost (accumulated cost) paths

Links represents biological characteristics such as dispersal ability within and between patches within the matrix


Application: Woodland Caribou

Boreal ecotype is threatened in Canada (COSEWIC 2002)

In southern Manitoba woodland caribou are generally sedentary

Habitat selection is strongest during winter months

Late seral Jack Pine stands and sparsely treed rock outcrops

High abundance of terrestrial lichens and low snow cover

Photo: Jared Hobbs (www.hobbsphotos.com)


The Owl Lake Woodland Caribou

WINTER HOME RANGE

GPS telemetry location data from Owl Lake herd (southeast MB)

Popn Size: 65 – 75

11 collared adults (9 male, 2 female)

Focused on winter points (Nov 1 – March 15)


Habitat Map and Cost Surface

Habitat Class

Cost

(OR-1)

JPD/STR 1

TMG/MCU 1.0077

MCL/IMU 1.7339

YNG/WL 3.5396

BURN 3.3029

WATER 3.5952


Graph Extraction

HIGH QUALITY PATCHES

LEAST COST LINKS


Graph Thresholding


Graph Thresholding


Graph Thresholding


Graph Thresholding

At each threshold compute a landscape level metric, Expected Cluster Size (ECS)

Expected Cluster Size: mean size of a cluster for randomly selected habitat cells

(area weighted mean cluster size at threshold distance, d)


Graph Thresholding


Are caribou responding to structural connectivity?

Point Expected Cluster Size

Telemetry points associated with the closest patch

At each threshold scale points are assigned the area of the cluster containing the associated patch

ECS is then computed from cluster sizes measured for each location point

This represents the expected size of a cluster of habitat associated for a randomly selected location point.



Randomization Test Point ECS computed for 100 sets of random points

distributed randomly in each habitat type in proportion to selection by caribou

Observed Point ECS compared to mean of random point sets

Distance thresholds where caribou points were greater than 95% CI, indicate scales at which caribou are more closely associated with highly connected clusters of high quality habitat than if randomly distributed within the home range



Differences greatest at scales between 500 – 1900 cost units

Above 1000 cost units, PECS for late winter points is 7,500ha and similar to maximum cluster size


Independent ValidationKississing Herd

NE of The Pas, MB

PATCHES FILTERED TO 25 ha

Historical home range

Current winter home range



Greatest differences at scales between 500 – 4500 cost units

Between 500 and 4500, PECS for late winter points is ~7,500 ha, but less than Max Cluster Size


Summary

1. Strong association between distribution of caribou and connected clusters of habitat

2. Affinity for clusters ~7500ha, and link thresholds 500 – 2000 cost units.

3. In the Owl Lake herd, caribou associated with clusters near the maximum cluster sizes at these thresholds.

4. Kississing also show strong affinity to larger clusters, but associated with clusters below the max available.

5. In the Kississing range availability of clusters is greater in both sizes and numbers; hence, greater potential for range expansion.


Conclusions

Spatial graphs are a useful method for assessing the connectivity of woodland caribou habitat

For identifying and mapping core areas of well connected habitat and can quantify how these areas contribute to overall landscape connectivity

For identifying scales where associations between caribou and connected habitat are strongest

Allows the patch definition to be scaled-up from inventory polygons to connected clusters which incorporate differential matrix quality


Conclusions

Increasing matrix quality may improve utilization of existing high quality habitat

Facilitate movement between patches (optimal foraging) Maintaining low densities (spacing out as an anti-predator

strategy)

Supports the idea that definition of critical habitat should include not only abundance but also spatial arrangement of high quality habitat, in addition to the relative quality of the intervening matrix habitat


Acknowledgements

Funding from Parks Canada Species at Risk Recovery Action and Education Fund

Field support was provided by Manitoba Conservation and Manitoba Hydro

Owl Lake GPS telemetry data collected as part of MB Hydro's Research and Development of Animal Borne Technology on Woodland Caribou Project

Participating partners: Manitoba Hydro Manitoba Model Forest Ltd. Manitoba Natural Resources Natural Resources Institute of the University of Manitoba TAEM Consultants.

Documents

Spatial Graphs for Assessing Woodland Caribou Habitat Connectivity Dan O’Brien, MSc, RPBio (Cortex Consultants Inc.) Micheline Manseau, PhD (Parks Canada)