Applications using a species-area
curve with habitat modifiers

The addition of measures of habitat heterogeneity into species-area
models will provide a significant improvement in their power to predict
species richness (Boecklen 1986). Boecklen and Gotelli (1984) deter-
mined that, for the 100 log-log species-area regressions reviewed by Con-
ner and McCoy (1979), on average these models explained about one-half
the variation in species richness (mean adj. r? = 0.49, standard deviation =
0.28). They recommend that other measures such as habitat heterogeneity
or resource availability be incorporated into the models to improve their
performance. In a test of a shelterbelt habitat model, Schroeder, Cable,
and Haire (1992) found that the inclusion of habitat conditions provided
more accurate predictions of breeding bird richness than area alone.

The effect of habitat quality on the species-area relationship was dis-
cussed by Zimmerman and Bierregaard (1986:139) in reference to central
Amazon forest frogs. They concluded that 100 ha containing quality
breeding habitat would preserve more species of frogs than 500 ha contain-
ing little, subquality, or even no critical habitat types. The implications of
this conclusion can be illustrated on a series of hypothetical species-area
curves (Figure 4). An area with low-quality habitat would be expected to
have a lower species-area curve than an area with high-quality habitat.
Thus, a small tract with high-quality habitat could have a higher suitabil-
ity index (more species) than a large tract with poor-quality habitat. To ef-
fect this change in the species-area formula, simply add a factor (0-1.0) to
account for habitat quality, as shown below:

S=cA* (habitat quality factor)

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation

15



tied to the defined objectives. For example, Askins, Philbrick, and Sugeno
(1987) found patch area to be positively related to the richness of forest in-
terior birds, but not related to the richness of all forest birds combined.
Possible modifiers for species richness measures include the following:

native, endemic, forest interior, area sensitive, locally rare or
threatened, cavity user, or taxonomic group (e.g., amphibi-
ans, breeding birds)

Use of these modifiers, where appropriate, will ensure that community
habitat evaluations do not overlook critical components of the community
and conform with defined objectives.

Developing and Using a Species-Area Curve

A species-area curve should be developed for the group of species that
relate to the defined wildlife objectives. The first step in developing the
species-area relationship is to determine the changes in species richness
associated with changes in area for the community of concern. A species-
area curve for the community may already exist, or may be constructed us-
ing data that describe the number of species found in different sized areas.
For example, Samson (1980) presents data on the number of prairie bird
species occurring on prairie islands in Missouri (Table 2). Entering this

Table 2
Species-Area Data for Tallgrass Prairie Islands in Central and
Southwest Missouri (from Samson 1980)

Prairie Bird Species Richness Area, ha
1 510.0
125.9

73.4
62.8

31.4
30.2
28.0
15.7

15.7

12.1

10.0
4.0

1.0
0.5

viniwoleloelalajajaloaloalol~

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation



References

Askins, R. A., Philbrick, M. J., and Sugeno, D. S. (1987). “Relationship
between the regional abundance of forest and the composition of forest
bird communities,” Biological Conservation 39, 129-152.

Blake, J. G. (1991). “Nested subsets and the distribution of birds on iso-
lated woodlots,” Conservation Biology 5, 58-66.

Blake, J. G., and Karr, J. R. (1984). “Species composition of bird com-
munities and the conservation benefit of large versus small forests,”
Biological Conservation 30, 173-187.

. (1987). “Breeding birds of isolated woodlots: Area and habitat
relationships,” Ecology 68(6), 1724-1734.

Boecklen, W. J. (1986). “Effects of habitat heterogeneity on the species-
area relationships of forest birds,” Journal of Biogeography 13, 59-68.

Boecklen, W. J., and Gotelli, N. J. (1984). “Island biogeographic theory
and conservation practice: Species-area or specious-area relation-
ships?” Biological Conservation 29, 63-80.

Bolger, D. T., Alberts, A. C., and Soule, M. E. (1991). “Occurrence pat-
terns of bird species in habitat fragments: Sampling, extinction, and
nested species subsets,” American Naturalist 137, 155-166.

Brown, M. and Dinsmore, J. J. (1988). “Habitat islands and the equilib-
rium theory of island biogeography,” Oecologia 75, 426-429.

Clark, T. W., and Zaunbrecher, D. (1987). “The greater Yellowstone eco-
system: The ecosystem concept in natural resource policy and manage-
ment,” Renewable Resources Journal 5(3), 8-16.

Conner, E. F., and McCoy, E. D. (1979). “The statistics and biology of
the species-area relationship,” American Naturalist 113(6), 791-833.

Cutler, A. (1991). “Nested faunas and extinction in fragmented habitats,”
Conservation Biology 5(4), 496-505.

Fahrig, L., and Merriam, G. (1994). “Conservation of fragmented popula-
tions,” Conservation Biology 8(1), 50-59.

References

19


This report should be cited as follows:

Schroeder, R. L. (1996). “Wildlife community habitat evaluation
using a modified species-area relationship,” Technical Report
WRP-DE-12, U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS.

The contents of this report are not to be used for advertising, publication,
or promotional purposes. Citation of trade names does not constitute an
official endorsement or approval of the use of such commercial products.

vii



16

1.0 T T T T
EAS
gt 4
% 0.8 >
z SS os
206 os pale ;
= a
8 ¥
sa =
2 0.4 Low valit habitat
©
F 02 4
fo) 1 1 1 1
) 100 200 300 400 500
Effective area (ha)

Figure 4.

Hypothetical species-area curves, showing the effects of
habitat quality

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation



22

Patterson, B. D., and Atmar, W. (1986). “Nested subsets and the struc-
ture of insular mammalian faunas and archipelagos.” Island biogeogra-
phy of mammals. L. R. Heaney and B. D. Patterson, ed., Academic
Press, London.

Picton, H. D. (1979). “The application of insular biogeographic theory to
the conservation of large mammals in the northern Rocky Mountains,”
Biological Conservation 15, 73-79.

Porneluzi, P., Bednarz, J. C., Goodrich, L. J., Zawada, N., and Hoover, J.
(1993). “Reproductive performance of territorial ovenbirds occupying
forest fragments and a contiguous forest in Pennsylvania,” Conserva-
tion Biology 7(3), 618-622.

Robbins, C. S., Dawson, D. K., and Dowell, B. A. (1989). “Habitat area
requirements of breeding forest birds of the middle Atlantic States,”
Wildlife Monographs 103, 34.

Robinson, S. K. (1990). “Effects of forest fragmentation on nesting
songbirds,” Illinois Natural History Survey Reports.

Samson, F. B. (1980). “Island biogeography and the conservation of prai-
rie birds,” North American Prairie Conference 7, 293-299.

Samson, F. B., and Knopf, F. L. (1982). “In search of a diversity ethic
for wildlife management,” North American Wildlife Conference 47,
421-431.

Schamberger, M., Farmer, A. H., and Terrell, J. W. (1982). “Habitat suit-
ability index models: Introduction,” U.S. Fish and Wildlife Service
FWS/OBS-82/10.

Schroeder, R. L. (1987). “Community models for wildlife impact assess-
ment: A review of concepts and approaches,” U.S. Fish and Wildlife
Service, Biological Report 87(2).

Schroeder, R. L. “Wildlife community habitat evaluation: A model for
deciduous palustrine forested wetlands in Maryland,” Technical Report
WRP-DE-14 (in preparation), U.S. Army Engineer Waterways Experi-
ment Station, Vicksburg, MS.

Schroeder, R. L., Cable, T. T., and Haire, S. L. (1992). “Wildlife species
richness in shelterbelts: Test of a habitat model,” Wildlife Society Bul-
letin 20, 264-273.

Schroeder, R. L., and Haire, S. L. (1993). “Guidelines for the develop-
ment of community-level habitat evaluation models,” U.S. Fish and
Wildlife Service, Biological Repart 8.

Schroeder, R. L., O’Neil, L. J., and Pullen, T. M., Jr. “Wildlife commu-
nity habitat evaluation: A model for bottomland hardwood forests of
the southeastern United States,” Technical Report in preparation, U.S.
Army Engineer Waterways Experiment Station, Vicksburg, MS.

References



18

6 Summary and
Recommendations

Based upon the literature and analyses of specific species-area data
sets, it appears that it is feasible to use the species-area relationship as the
basis for assessing wildlife community habitat. The essence of the ap-
proach recommended here is as follows:

a. Define the wildlife resource objectives for the region of interest. If
these objectives include concerns about area sensitive species, inte-
rior species, species richness (overall or of selected groups), or habi-
tat fragmentation, then use of the species-area relationship may be
appropriate.

b. Develop a species-area curve for the defined objective.

c. Determine the need for computing the effective area, based on factors
for isolation or permeability.

d. Determine the need to modify the species-area relationship based on
habitat quality factors.

The essence of this approach is represented by a family of species-area
curves (Figure 4). The input value on the x-axis is effective area, to take
into account the effects of landscape context on species richness. The fam-
ily of curves represents the effects of various levels of habitat quality on
richness. This basic approach is supported both conceptually in the litera-
ture and by the independent data sets presented.

For users who will actually be developing their own community-level
habitat assessment models, it is highly recommended that the models fol-
low the guidelines presented in an earlier report (Schroeder and Haire
1993).

Chapter 6 Summary and Recommendations


A limitation of using only area is that species richness is often affected
by the landscape context of an area and its internal habitat quality. An ad-
vantage of using only area is that it would allow a rapid evaluation of
many sites over a large region. In addition, knowledge of the distribution
of patch sizes in a specific region may be useful in conducting cumulative
impact assessments (Gosselink and Lee 1987).

Applications using a specles-area curve
with modifications for landscape context

A basic premise of the theory of island biogeography is that the species
richness of an island (habitat patch) is affected by its isolation from other
patches (MacArthur and Wilson 1967). Isolated patches generally contain
fewer species than nonisolated patches. Patch isolation is determined by
several factors, including the distance to other patches (Lomolino 1982),
the amount of similar habitat in the surrounding landscape (Brown and
Dinsmore 1988), and the characteristics of the intervening landscape
(Knaapen, Scheffer, and Harms 1992). Wilcove, McLellan, and Dobson
(1986) believe the influence of corridors is debatable; they believe it is
more useful if the land around patches allows species to exist at least mar-
ginally, and thus be able to diffuse into other patches.

Robbins, Dawson, and Dowell (1989), in a study of eastern forest
birds, note that the proximity to other forests appears to enhance the effec-
tive area of an isolated patch. This author proposes that the concept of ef-
fective area can be used as a basis for modifying the area of a patch prior
to predicting species richness from a species-area curve and uses two exist-
ing data sets to illustrate this point.

Brown and Dinsmore (1988) analyzed the species richness of breeding
birds in Iowa marshes and determined that richness was a function of both
area and isolation (expressed as the number of marsh hectares within 5 km).
The species-area formula determined from their data was as follows:

Breeding bird richness = 7.797 (Area-ha)? 149

Corrected r” = 0.584

This author used their measure of isolation (expressed as the number of
marsh hectares within 5 km) to modify the actual area of each marsh and
to determine its effective area. The area of marshes that were highly iso-
lated was left unchanged, and the area of marshes that were the least iso-
lated was arbitrarily increased by a factor of four. A linear relationship
was assumed between these two extremes. Based upon a computation of
effective marsh area, the revised species-area formula from their data was
as follows:

Breeding bird richness = 7.161 (Effective Area-ha)°:!54

Corrected r? = 0.652

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation

13



Table 1 (Concluded)

Species Area Sensitive

Forest Interior

Golden-crowned kinglet (Regulus satrapa)

x

Blue-gray gnatcatcher (Polioptila caerulea) x

Veery (Catharus fuscescens)

Swainson’s thrush (Catharus ustulatus)

Hermit thrush (Catharus guttatus)

Wood thrush (Hylocichla mustelina)

Yellow-throated vireo (Vireo flavifrons)

Red-eyed vireo (Vireo olivaceus)

x |x |< |x [ox

Chestnut-sided warbler (Dendroica pensyivanica)

Magnolia warbler (Dendroica magnolia)

Black-throated blue warbler (Dendroica caerulescens) | X

Yellow-rumped warbler (Dendroica coronata)

Black-throated green warbler (Dendroica virens) x

Blackburnian warbler (Dendroica fusca)

Yellow-throated warbler (Dendroica dominica)

Pine warbler (Dendroica pinus)

Cerulean warbler (Dendroica cerulea)

Black and white warbler (Mniotilta varia)

American redstart (Setophaga ruticilla)

Worm-eating warbler (Helmintheros vermivorous)

Ovenbird (Seiurus aurocapilus)

Northern waterthrush (Seiurus noveboracensis)

Louisiana waterthrush (Seiurus motacilla)

Kentucky warbler (Oporornis formosus)

* | | >< |< [oe |e fe | >< fe fe | >< | J oe J >< | ><

Mourning warbler (Oporornis philadelphia)

Hooded warbler (Wilsonia citrina)

x

Canada warbler (Wilsonia canadensis)

Summer tanager (Piranga rubra)

Scarlet tanager (Piranga olivacae)

x fx [x |x fox fx fos fox pe fos fox | >< fos [><

Rose-breasted grosbeak (Pheucticus ludovicianus)

To be most effective, management strategies should concentrate on the
species most in need of protection (Blake and Karr 1984). Management
for small areas often will not accomplish this objective. Data from Whit-
comb et al. (1981) indicate that forest interior birds are rare at a regional
scale. Local extinctions of birds requiring forest interior conditions have
been documented (Newmark 1991). To conserve regional biodiversity,
maintenance of habitats for species with large-area needs is essential.

Chapter 2 Influence of Area on Wildlife Community Composition and Productivity



(1985:884) summarized the concerns of many ecologists in Stating that
“habitat fragmentation is the most serious threat to biological diversity
and is the primary cause of the present extinction crisis.” Application of
knowledge gained from current understanding of the species-area relation-
ship is an important starting point in decreasing this threat.

Chapter 1. Introduction


1 Introduction

The assessment and management of wildlife habitat has historically fo-
cused on individual species. The U.S. Fish and Wildlife Service’s Habitat
Evaluation Procedures (U.S. Fish and Wildlife Service 1980) and over
150 Habitat Suitability Index Models (Schamberger, Farmer, and Terrell
1982) were developed primarily to provide a systematic, replicable, and
quantitative method to evaluate species’ habitat. In recent years, increas-
ing numbers of scientists and field biologists have shifted their emphasis
to investigation of community- and ecosystem-level habitat relationships.

A wealth of literature has been published that addresses both the theory
and concepts of the emerging field of conservation biology, particularly
that aspect dealing with community- and landscape-level issues (Samson
and Knopf 1982; Harris 1984; Forman and Godron 1986; Noss 1990; and
many others). On the other hand, the development of practical tools and
methods for use of these concepts by field biologists has proceeded at a
much slower pace. Several published community-level models were re-
viewed in an earlier report (Schroeder 1987), and additional community
models are being developed (Schroeder, O’Neil, and Pullen, in prepara-
tion; Schroeder, in preparation).

For many locations, however, community-level models will not be avail-
able for several years. In the interim, much can be done to incorporate ex-
isting knowledge of the principles of community ecology into field office
operations. The purpose of this report is to explore the feasibility of using
the species-area relationship as a basis for assessing the quality of habitat
for a specific wildlife community.

Many wildlife species are declining because of direct habitat losses,
and because remaining habitat fragments are too small for their continued
existence. Of special concern are certain bird species (Blake 1991) and
large carnivorous mammals (Harris 1988). Wilson (1985) described the
general principle from island biogeography that when the area of a re-
gional habitat is reduced to one-tenth its original extent, the number of
species will eventually decline to one-half the original number. In areas
where habitat loss and fragmentation are considerably advanced, McLel-
lan et al. (1986) recommended that special priority be given to maintain-
ing the integrity of the remaining large fragments. Wilcox and Murphy

Chapter 1 Introduction


14

Lomolino (1992) analyzed the species richness of mammals on islands
in the St. Lawrence River and determined that richness was also a function
of area and isolation (expressed as the distance to the nearest mainland or
large island). The species-area formula determined from their data was as
follows:

Mammalian richness = 6.489 (Area-ha)°352

Corrected r” = 0.879

Again, this author used their measure of isolation (distance to nearest
mainland or large island) to modify the actual area of each island and to
determine its effective area. The area of islands that were highly isolated
was left unchanged, and the area of islands that were the least isolated
was increased by a factor of four. A linear relationship was assumed be-
tween these two extremes. Based upon a computation of effective island
area, the revised species-area formula from their data was as follows:

Mammalian richness = 4.979 (Effective Area-ha)?>76

Corrected r” = 0.936

In each of these two examples, the use of effective area provided a bet-
ter fit than the use of area alone in estimating species richness.

The degree to which a patch boundary deflects the movement of an ani-
mal is known as the boundary permeability (Wiens, Crawford, and Gosz
1985). Permeability is related to characteristics of both the animal and
the boundary itself. The intervening habitat structure, resource levels, and
presence or absence of predators or competitors can influence the move-
ment of an animal from one patch to another. Patches of habitat with ideal.
structural characteristics will not be usable unless the wildlife species of
concern can move freely between patches and maintain genetic continuity
with conspecifics (Harris and Kangas 1988). Knaapen, Scheffer, and
Harms (1992) developed an index to evaluate permeability based on the
characteristics of the intervening landscape. Their measure, the minimal
cumulative resistance (MCR) index, is based upon the likelihood of disper-
sal of different species groups across various landscape types or barriers.
Empirical data were not provided on species-area relationships and the
MCR. It would seem likely, however, that patches in landscapes with high
resistance values would have less effective area than patches in landscapes
that were more permeable.

Applications of the species-area curve with landscape modifiers will be
enhanced by use of Geographic Information Systems (GIS) technology. A
model being develop for bottomland hardwoods of the Southeast
(Schroeder, O’Neil, and Pullen, in preparation) incorporates measures of
both isolation and permeability and has been fully automated for use with
the ARC/INFO GIS software.

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation


National Park (Clark and Zaunbrecher 1987). Zeveloff (1983) estimated
that 40,000 ha (99,000 acres) per reserve area was needed to maintain a vi-
able black bear population. Whereas very few habitats of these sizes ex-
ist, it is clear that long-term maintenance of these or smaller carnivores
will require large habitat areas.

Studies of eastern forest bird communities have resulted in the classifi-
cation of a large number of birds as either area sensitive or preferring for-
est interior conditions. Robbins, Dawson, and Dowell (1989) list 26
area-sensitive species, 19 of which are neotropical migrants. Freemark
and Collins (1992) compiled a list of eastern forest birds classified as
either area sensitive or preferring forest interior conditions (Table 1).
Breeding success of neotropical migrants in forest fragments in Illinois
was extremely low due to high predation rates (80 percent of all nests) and
brood parasitism by brown-headed cowbirds (Molothrus ater) (76 percent
of all nests) (Robinson 1990). Large forest plots had significantly higher
nesting success for ovenbirds (Seiurus aurocapillus) than forest fragments
(Porneluzi et al. 1993). Habitat patches necessary for supporting viable
populations of certain bird species may need to be larger than the size ex-
pected based on surveys of singing males only (Gibbs and Faaborg 1990).

Table 1
Eastern Forest Birds Classified as Either Area Sensitive or
Forest Interior Occupants (from Freemark and Collins 1992)

Species Area Sensitive | Forest Interior

Cooper's hawk (Accipiter cooperii) x

Red-shouldered hawk (Buteo fineatus) x

Broad-winged hawk (Buteo platypterus)
Barred owl (Strix varia)

x

Red-bellied woodpecker (Melanerpes carolinus)

Hairy woodpecker (Picoides villosus)

Pileated woodpecker (Dryocopus pileatus)

ad

Olive-sided flycatcher (Contopus borealis)

x |x | >< |x

Acadian flycatcher (Empidonax virescens)

Least flycatcher (Empidonax minimus)

Great crested flycatcher (Myiarchus crinitus)

«|x |< |

American crow (Corvus brachyrhynchos)

Common raven (Corvus corax) x

Tufted titmouse (Parus bicolor) x

Red-breasted nuthatch (Sitta canadensis)

White-breasted nuthatch (Sitta carolinensis)

Brown creeper (Certhia americana) x

[>< |< |<

Winter wren (Troglodytes troglodytes)

(Continued)

Chapter 2 Influence of Area on Wildlife Community Composition and Productivity



20

Forman, R. T. T., and Godron, M. (1986). Landscape ecology. John
Wiley and Sons, New York.

Freemark, K., and Collins, B. (1992). “Landscape ecology of birds breed-
ing in temperate forest fragments.” Ecology and conservation of neo-
tropical birds. J. W. Hagan III and D. W. Johnston, ed., Smithsonian
Institution Press, 443-453.

Galli, A., Leck, C. F., and Forman, R. T. T. (1976). “Avian distribution
patterns in forest islands of different sizes in central New Jersey,” Auk
93, 356-364.

Gibbs, J. P., and Faaborg, J. (1990). “Estimating the viability of oven-
bird and Kentucky warbler populations in forest fragments,” Conserva-
tion Biology 4, 193-196.

Gosselink, J. G., and Lee, L. C. (1987). “Cumulative impact assessment
in bottomland hardwood forests,” Center for Wetland Resources, Lou-
isiana State University, Baton Rouge, LA.

Graber, J. W., and Graber, R. R. (1976). “Environmental evaluations us-
ing birds and their habitats,” Illinois Natural History survey Biological
Note 97,

Gutzwiller, K. J., and Anderson, S. H. (1987). “Multiscale associations
between cavity-nesting birds and features of Wyoming streamside
woodlands,” Condor 89, 534-548.

Harris, L. D. (1984). The fragmented forest, island biogeographic theory
and the preservation of biotic diversity. University of Chicago Press,
Chicago, IL.

. (1988). “The nature of cumulative impacts on biotic diversity of _
wetland vertebrates,” Environmental Management 12, 675-693.

Harris, L. D., and Kangas, P. (1988). “Reconsideration of the habitat con-
cept,” Transactions North American Wildlife and Natural Resources
Conference 53, 137-144.

Hayden, T. J., Faaborg, J., and Clawson, R. L. (1985). “Estimates of
minimum area requirements for Missouri forest birds,” Transactions
Missouri Academy of Sciences 19, 11-22.

Hemesath, L. M., and Dinsmore, J. J. (1993). “Factors affecting bird
colonization of restored wetlands,” Prairie Naturalist 25(1), 1-11.

Humphreys, W. F., and Kitchener, D. J. (1982). “The effect of habitat
utilization on species-area curves: Implications for optimal reserve
area,” Journal of Biogeography 9, 391-396.

Johns, B. W. (1993). “The influence of grove size on bird species rich-
ness in aspen parklands,” Wilson Bulletin 105(2), 256-264.

References



Wetlands Research Program Technical Report WRP-DE-12
July 1996

Wildlife Community Habitat Evaluation
Using a Modified Species-Area Relationship

by Richard L. Schroeder

National Biological Service
Midcontinent Ecological Science Center
4512 McMurry Avenue

Fort Collins, CO 80525-3400

Final report
Approved for public release; distribution is untimited

Prepared for U.S. Army Corps of Engineers
Washington, DC 20314-1000



r

50 T T T T T

Bird species richness

Area (ha)

Figure 1. Example of a species-area curve using data from 34 Kansas
shelterbelts

likely to contain a higher diversity of habitats than smaller areas. Third,
larger areas are more likely to be filled by species dispersing randomly
from a source pool of species. Regardless of the causal mechanisms of
the species-area relationship, it has been shown to be true in a wide vari-
ety of situations.

Application of concepts from the species-area relationship and princi-
ples of island biogeography during the late 1970s often focused on the
issue of whether a single large or several small reserves were the best for
conservation (Simberloff and Abele 1976 and subsequent replies).
Whereas various arguments have been presented to show that the numbers
of species can vary in these two scenarios, the important issue for conser-
vation is to identify the species composition of these communities and
evaluate this information in relation to conservation goals.

Chapter 3 Explanation of the Species-Area Relationship


3 Explanation of the
Species-Area Relationship

The fact that the number of species increases in direct relation to the
size of the area sampled has been clearly established in the study of com-
munity ecology. This relationship was explored on islands (MacArthur
and Wilson 1967) and later extended to interior habitats, including iso-
lated forests (Galli, Leck, and Forman 1976), prairies (Samson 1980),
mountain ranges (Picton 1979), and wetlands (Tyser 1983). The species-
area relationship has been demonstrated for birds (Blake and Karr 1987;
Johns 1993), mammals (Lomolino 1982), reptiles (Jones, Kepner, and
Martin 1985), amphibians (Laan and Verboom 1990), invertebrates (Mur-
phy and Wilcox 1986), and plants (Wade and Thompson 1991). The gen-
eral equation describing the species-area relationship is most often
expressed as:

S=cA?
where
S = number of species
c =a constant that varies with taxon and geographic region
A =area
z =a constant measuring the slope of the line relating S and A
The general shape of a species-area curve is shown in Figure 1. This
curve was developed from data on bird use of shelterbelts in Kansas
(Schroeder, unpublished data). The form of the curve indicates that the
number of species increases very rapidly with initial increases in area, and
then less rapidly for larger areas.
Conner and McCoy (1979) summarized three possible explanations for
the fact that species numbers increase with area. First, larger areas in-

crease the likelihood of colonization by new species and decrease the
chances of extinction of existing species. Second, larger areas are more

Chapter 3 Explanation of the Species-Area Relationship


2 Influence of Area on
Wildlife Community
Composition and
Productivity

Recent studies have indicated that the composition of wildlife commu-
nities varies in a nonrandom fashion with changes in area of habitat. Pat-
terson and Atmar (1986) noted that the distribution of mammals in
southwestern mountain ranges of various sizes occurred in a nested fash-
ion. This nested distribution indicates that the species that occur in
smaller sized habitat patches are a subset of the species that occur in
larger patches. Birds in isolated woodlots in central Illinois also exhibited
a nested subset pattern of distribution; small habitat patches contained
more generalist bird species, whereas larger patches often contain species
with more specialized resource requirements (Blake 1991). This nonran-
dom, nested pattern of occurrence has been observed in a variety of com-
munities and geographic locations (e.g., bird communities in Missouri
(Hayden, Faaborg, and Clawson 1985) and California (Bolger, Alberts,
and Soule 1991), populations of mammals, passerine birds, and lizards in
western Australia (Humphreys and Kitchener 1982), boreal mammals and
birds in the Great Basin (Cutler 1991), and reptiles in western Arizona
(Jones, Kepner, and Martin 1985)).

The implications of the nested subset distribution are important in un-
derstanding why area can be used as a basis for wildlife habitat evalu-
ations in some communities. If the species that only occur in the large
areas are of concern from a conservation viewpoint, then consideration of
area is mandated. Two groups of species that have received the most atten-
tion in relation to their need for large areas are large mammalian carni-
vores and area-sensitive or forest interior birds.

Animals at higher trophic levels generally require larger areas than
those at lower trophic levels (Harris 1988). It has been estimated that ade-
quate protection of grizzly bears (Ursus arctos) would require an area sev-
eral times larger than the 890,000 ha (2,200,000 acres) of Yellowstone

Chapter 2. Influence of Area on Wildlife Community Composition and Productivity



5 Limitations of Using the
Species-Area Relationship

There are several potential limitations of using the species-area rela-
tionship as a basis for wildlife community habitat evaluation. First, most
of the existing data for species-area relationships in North America is de-
rived from avian studies. Information is especially weak on reptiles and
amphibians, which are important vertebrate groups in many regions. Sec-
ond, the emphasis on the value of large areas does not take into account
the possible value of small areas for certain species. For example, Moler
and Franz (1987) describe the value to amphibians and wading birds of
small isolated wetlands in the southeastern coastal plain. They note that
several species of amphibians are dependent on small, isolated wetland
habitats that are free of predators. In addition, rare or endangered plants
or animals may occur on small patches. As noted earlier, the critical ques-
tion that must be addressed is the conservation goal for the region of con-
cern. Whereas protection of large areas may be desired for many goals, it
is essential not to ignore potential values of small, unique patches.

With multispecies assemblages as the focus of conservation efforts, the
probability that community features will be affected by factors outside the
specified boundaries increases dramatically with species number and vari-
ety (Van Horne and Wiens 1991). Models for regional populations should
consider a landscape larger than a single patch and its immediate surround-
ings and should account for the interactions between patches (Kushlan
1983; Fahrig and Merriam 1994). Assessment of species richness on a re-
gional scale will require a more complex approach than presented here for
assessing species richness in individual patches. Additional research into
factors affecting regional scale biodiversity is needed.

Chapter 5 Limitations of Using the Species-Area Relationship

17


Simberloff, D. S., and Abele, L. G. (1976). “Island biogeographic theory
and conservation practice,” Science 191, 285-286.

Tyser, R. W. (1983). “Species-area relations of cattail marsh avifauna,”
Passenger Pigeon 45, 125-128.

U.S. Fish and Wildlife Service. (1980). “Habitat evaluation procedures
(HEP).” Division of ecological services. ESM 102.

Van Horne, B., and Wiens, J. A. (1991). “Forest bird habitat suitability
models and the development of general habitat models.” U.S. Fish and
Wildlife Service, Fish and Wildlife Research 8, 31.

Wade, G. L., and Thompson, R. L. (1991). “The species-area curve and
regional floras,” Transactions Kentucky Academy of Science 52, 21-26.

Whitcomb, R. F., Robbins, C. S., Lynch, J. F., Whitcomb, B. L.,
Klimkiewicz, M. K., and Bystrak, D. (1981). “Effects of forest frag-
mentation on avifauna of the eastern deciduous forest.” Forest island
dynamics in man-dominated landscapes. R. L. Burgess and D. M.
Sharpe, ed., Springer-Verlag, New York.

Wiens, J. A., Crawford, C. S., and Gosz, J. R. (1985). “Boundary dynam-
ics: A conceptual framework for studying landscape ecosystems,”
Oikos 45(3), 421-427.

Wilcove, D. S., McLellan, C. H., and Dobson, A. P. (1986). “Habitat
fragmentation in the temperate zone.” Conservation biology: The sci-
ence of scarcity and diversity. M. E. Soule, ed., Sinauer Associates,
Inc., Sunderland, MA.

Wilcox, B. A., and Murphy, D. D. (1985). “Conservation strategy: The

effects of fragmentation on extinction,” American Midland Naturalist
125, 879-887.

Wilkerson, L. (1988). SYSTAT: The system for statistics. SYSTAT, Inc.
Evanston, IL.

wilson, BO. (1985). “The biological diversity crisis,” Bioscience 35,

Zeveloff, S. I. (1983). “Island biogeographic considerations for pocosin

wildlife conservation,” Journal of the Elisha Mi ientifi i
3o8) eer of the Elisha Mitchell Scientific Society

Zimmerman, B. L., and Bierregaard, R. O (1986). “
rman, . »R.O. - “Relevance of the
equilibrium theory of island biogeograph: id ies-; i
conservation with a case from \mazoniac” Jourhal of Bear sesstions (0

13, 133-143. Amazonia,” Journal of Biogeography

References

U.S. GOVERNMENT PRINTING OFFICE: 1996-733-144/40004

23



vi

Preface

The work described in this report was authorized by Headquarters, U.S.
Army Corps of Engineers (HQUSACE), as part of the Delineation and
Evaluation Task Area of the Wetlands Research Program (WRP). The
work was performed under Work Unit 32756, “Evaluation of Wetland
Functions and Values,” for which Mr. Ellis J. Clairain, Jr., was Technical
Manager: Mr. John Bellinger (CECW-PO) was the WRP Technical Moni-
tor for this work.

Mr. Dave Mathis (CERD-C) was the WRP Coordinator at the Director-
ate of Research and Development, HQUSACE; Mr. William L. Klesch
(CECW-PO) served as the WRP Technical Monitor’s Representative;

Dr. Russell F. Theriot, U.S. Army Engineer Waterways Experiment Station
(WES), was the Wetlands Program Manager. Mr. Clairain, WES, was the
Task Area Manager.

This work was performed by Mr. Richard L. Schroeder, National Bio-
logical Service, Midcontinent Ecological Science Center, Fort Collins,
CO. Mr. R. Daniel Smith, Wetlands Branch, Environmental Laboratory
(EL), WES, was the Project Manager under the general supervision of
Mr. Clairain, Chief, Wetlands Branch; Dr. Conrad J. Kirby, Chief, Ecologi-
cal Research Division, EL; Dr. Edwin A. Theriot, Assistant Director, EL;
and Dr. John W. Keeley, Director, EL.

Individual reviewers assisting with their thoughtful and constructive
comments were Messrs. A. H. Farmer and R. G. Osborn.

At the time of publication of this report, Director of WES was
Dr. Robert W. Whalin. Commander was COL Bruce K. Howard, EN.



10

data into a statistical program (e.g., the Nonlin module of SYSTAT (Wilk-
erson 1988)) allows calculation of the species-area formula and curve for
this community (Figure 2).

Prairie bird species richness

°% 100 200 300 400 500 600

Area (ha)

Figure 2. Species-area curve for prairie birds

Information on species-area relationships from a variety of geographic
locations and community types across North America is provided in Table 3.
This information, or similar data acquired from local studies, can be used
to predict the effects of changes in area on species richness and incorpo-
rated into community-level habitat evaluations. Most of these data were
derived from bird community studies. Species-area data for other wildlife
groups are less common in the literature.

Developing an index from a species-area curve

Most habitat assessment models make use of simple unitless indices to
rate and compare different habitats (e.g., the 0-1 scale of Habitat Suitabil-
ity Index models (Schamberger, Farmer, and Terrell 1982)). Whereas
most habitat variables have a logical point at which to assign a maximum
index value, this is not true with the species-area relationship. In theory,
species richness would continually increase with area, and, therefore, a
maximum index value would never be obtained. In practice, however, it
may be necessary to determine a specific size at which to assign a maxi-
mum index value.

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation



12

The community model for bottomland hardwood forested wetlands being
developed by Schroeder, O’ Neil, and Pullen (in preparation) recommends
that a maximum index (1.0) be assigned to 3,000-ha tracts (Figure 3). The
3,000-ha size was selected by determining which species were important
and how large an area they would require to be present. In a test of a shel-
terbelt community model, Schroeder, Cable, and Haire (1992) recommend
that the maximum index be assigned to the largest shelterbelt expected to
be encountered in the area of application. The latter approach allows the
index to be scaled to local or regional conditions, but makes it invalid to
compare habitats outside of the designated area.

id
©

o
o

o
A

Tract Suitability Index

°
i
T

1

0 L 1
0 1000 2000 3000

Effective area (ha)

Figure 3. Scaling the species-area curve to yield a 0-1.0 index

It is not absolutely necessary to convert the species-area relationship to
an index. The output can remain in direct units of species richness, and
comparisons or decisions made from this basis.

Simple applications using a species-area curve

A community-level habitat evaluation could be conducted using only a
species-area curve to rate and compare habitats. Such an evaluation
would be most suited to situations where internal habitat conditions were
reasonably similar, and where the landscape context was not an important
factor. In such situations, area alone should be expected to account for
most of the variation in the measure of richness being assessed.

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation


Contents

Preface 2... eee ee eee vi
1—Introduction . 2... eee 1

2—Influence of Area on Wildlife Community Composition

and Productivity... 2.2... .........00..0.....0000, 3
3—Explanation of the Species-Area Relationship ............ 6
4—Use of the Species-Area Relationship in Wildlife Community

Habitat Evaluation .........................0.. 8

Defining Community Boundaries .............. 8
Defining Species Richness ............ 8
Developing and Using a Species-Area Curve 9
Developing an index from a species-area curve 10
Simple applications using a species-area curve 12
Applications using a species-area curve with modifications
for landscape context... 2... ......00...0-0004 13
Applications using a species-area curve with habitat
modifiers ........... 0... .0...... 00.000. 15
5—Limitations of Using the Species-Area Relationship. ........ 17
6—Summary and Recommendations. ................... 18
References... eee eee 19

SF 298


Jones, K. B., Kepner, L. P., and Martin, T. E. (1985). “Species of rep-
tiles occupying habitat islands in Western Arizona: A deterministic as-
semblage,” Oecologia 66, 595-601.

Knaapen, J. P., Scheffer, M., and Harms, B. (1992). “Estimating habitat
isolation in landscape planning,” Landscape and Urban Planning 23,
1-16.

Kushlan, J. (1983). “Special species and ecosystem preserves: Colonial
waterbirds in U.S. national parks,” Environmental Management 11,
109-119.

Laan, R., and Verboom, B. (1990). “Effects of pool size and isolation on
amphibian communities,” Biological Conservation 54, 251-262.

Lomolino, M. V. (1982). “Species-area and species-distance relation-
ships of terrestrial mammals in the Thousand Island Region,” Oecolo-
gia 54, 72-75.

MacArthur, R. H., and Wilson, E. O. (1967). “The theory of island bio-
geography,” Monographs in population Biology 1. Princeton Univer-
sity Press, New Jersey.

McLellan, C. H., Dobson, A. P., Wilcove, D. S., and Lynch, J. F. (1986).
“Effects of forest fragmentation on new- and old-world bird communi-
ties: Empirical observations and theoretical implications.” Wildlife
2000: Modeling habitat relationships of terrestrial vertebrates. J.
Verner, M. L. Morrison, and C. J. Ralph, ed., University of Wisconsin
Press, Madison, 305-313.

Moler, P. E., and Franz, R. (1987). “Wildlife values of small, isolated
wetlands in the southeastern coastal plain.” Southeastern nongame and
endangered wildlife symposium. R. R. Odom, K. A. Riddleberger, and
J. C. Ozier, ed., Georgia Department of Natural Resources, 234-241.

Murphy, D. D., and Wilcox, B. A. (1986). “Butterfly diversity in natural
habitat fragments: A test of the validity of vertebrate based manage-
ment.” Wildlife 2000: Modeling habitat relationships of terrestrial
vertebrates.” J. Verner, M. L. Morrison, and C. J. Ralph, ed., Univer-
sity of Wisconsin Press, Madison, 287-299.

Newmark, W. D. (1991). “Tropical forest fragmentation and the local ex-
tinction of understory birds in the eastern Usambara Mountains, Tanza-
nia,” Conservation Biology 5, 67-78.

Noss, R. F. (1990). “Can we maintain biological and ecological integ-
rity?” Conservation Biology 4, 241-243.

Odum, E. P. (1971). Fundamentals of ecology. Saunders, Philadelphia,
PA.

References

21


Corps of Engineers Research Report Summary, July 1996

Wildlife Habitat Evaluation

\

Wildlife Community Habitat Evaluation Using a Modified Species-Area

Relationship (TR WRP-DE-12)

ISSUE:

Habitat assessment has typically focused on one
or several individual species. Guidelines are
needed for the development of community-level
assessment methods.

OBJECTIVE:

These general guidelines for developing
wildlife community habitat models will provide
Corps field biologists with an improved
understanding of applications of the principles
of community ecology. These guidelines meet
the need of the field biologist under Section 404
of the Clean Water Act to prevent or mitigate for
habitat impacts to wetlands by aiding in the
assessment of models to evaluate wildlife
community habitat value under different spatial
scales.

SUMMARY:

This document provides guidance on using
species-area relationships to develop wildlife
community habitat models. Establishing clear
wildlife resource objectives is important prior to
model development. Different measures of

species richness can be used to meet different
objectives. Species-area curves can be used
independently or with either spatial or habitat
modifiers. The use of spatial or habitat modifiers
improves the power of the species-area
relationship in predicting species richness.
Limitations of using the species-area
relationship include the possibility of
overlooking the value of small areas for certain
species and the difficulty in considering the
effects of regional dynamics on species
richness.

AVAILABILITY OF REPORT:

This report is available on Interlibrary Loan
Service from the U.S. Army Engineer
Waterways Experiment Station (WES) Library,
3909 Halls Ferry Road, Vicksburg, MS
39180-6199, telephone (601) 634-2355.

To purchase a copy, call the National Technical
Information Service (NTIS) at (703) 487-4650.
For help in identifying a title for sale, call (703)
487-4780.

NTIS report numbers may also be requested
from the WES librarians.

Please reproduce this page locally, as needed.


4 Use of the Species-Area
Relationship in Wildlife
Community Habitat
Evaluation

Defining Community Boundaries

Use of the species-area relationship requires that the boundaries of the
area of concern be accurately delineated. The species-area relationship
was first described for true island habitats, where boundaries were clearly
marked by the water’s edge. Defining boundaries for inland areas can be
more difficult. Odum (1971) defines a community as an assemblage of
populations living within a prescribed area or physical habitat. For most
field applications, the area of concern can be identified by delineating spe-
cific vegetation communities. For example, the species-area relationship
could be applied to a forest stand isolated by crops or pasture. In some
situations, the area of concern could be defined by spatial limits, such as a
wetland/upland complex defined as all habitats within 100 m of the wet-
land edge. In all cases, the definition of community boundaries is some-
what arbitrary and should be explained fully.

Defining Species Richness

Different measures of species richness can be used to meet different ob-
jectives. The most general measure of species richness is simply a count
of all species occurring in the community of interest. Such a general
measure provides only a broad view of the community. Two areas could
contain the same number of species, but be quite different in terms of
which species were present.

Species richness may be modified by describing a particular group or
subset of the entire community that is of most interest and more closely

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaiuation


oy

Table 3

Species-Area Formulas for Various Habitats and Geographic

Locations

Locations, Source

Richness Measure, Y

R?

Formula

East-central Illinois
woodlots - 1979 (Blake
1991)!

Breeding birds

0.828

Y = 14.35 * (areaha)*'7

New Jersey oak forests
(Galli, Leck, and Forman
1976)!

Breeding birds

0.962

Y = 16.33 * (areaha)”2*

Missouri prairies (Samson
4980)"

Prairie birds

0.927

Y = 1.94 * (areaha)?-?62

Wisconsin cattail marsh
(Tyser 1983)'

Wetland birds

0.921

Y = 5.27 * (areaha)? 325

Kansas shelterbelts
(Schroeder, unpubl. data)

Breeding birds

0.792

Y = 17.36 * (areaha)”**9

Central Nevada riparian
canyons (Murphy and
Wilcox 1986)

Birds

0.60

Y = 1.46 * (areaha)°-*49

Illinois southern lowland
hardwoods (Graber and
Graber 1976)!

Breeding birds

0.946

Y = 12.8 * (areaha)??75

\ilincis upland hardwoods
{Graber and Graber
1976)!

Breeding birds

0.948

Y =6.01 * (areaha)*-417

Illinois shrub habitats
(Graber and Graber
1976)'

Breeding birds

0.869

Y = 9.71 * (areaha)?976

Illinois north and central
pastures (Graber and
Graber 1976)!

Breeding birds

0.948

Y = 3.91 * (areaha)?-?85

St. Lawrence River
islands (Lomolino 1982)

Terrestrial mammals

0.86

Y = 6.51 * (areaha)®95

lowa seasonal and semi-
permanent marshes
{Brown and Dinsmore
1988)

Breeding birds

0.68

Y = 6.0* (areaha)??9

lowa restored wetlands
(Hemesath and Dinsmore
1993)

Breeding birds

0.24

log Y = log 0.71 + 0.434
log (areaha)

Saskatchewan aspen
groves (Johns 1993)!

Breeding birds

0.718

Y = 11.79 * (areaha)?-0?

Wyoming floodplains
(Gutzwiller and Anderson
1987)!

Cavity nesting birds

0.792

Y = 1.84 * (areaha)°-*45

iv Species-area formulas were calculated from raw data in sources noted, using the Nonlin
program in SYSTAT (Wilkerson 1988).

Chapter 4 Use of the Species-Area Relationship in Wildlife Community Habitat Evaluation

11