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Recommendations for Monitoring Amphibians
at Multiple Spatial Scales
Karen M. Dvornich
Washington Cooperative Fish and Wildlife Research Unit
University of Washington
Box 357980
Seattle, WA 98195-7980
kgap@salmo.cqs.washington.edu
and
Kelly R. McAllister
Washington Department of Fish and Wildlife
600 Capitol Way N.
Olympia, WA 98501
mcallkrm@dfw.wa.gov
The Washington State Gap Analysis Project (WAGAP) is part of a national program
which seeks to enhance conservation of biological diversity by identifying plant
communities and terrestrial vertebrate species that are underrepresented on lands
managed for biodiversity (Scott et al. 1993). Typically, species occurrence data
and published information on habitat affinities are used to create models of each
species' range so that species richness analyses can be completed over large geographic
areas.
Historically, amphibian specimens collected and deposited in herpetological collections
have been accompanied by very little documentation. A complete lack of habitat
information has been the rule rather the exception. President Clinton's Forest
Ecosystem Management Assessment Team (FEMAT, 1993) found few data available for
amphibians, and what were available were distributed throughout museums, agencies,
timber companies and private collections in a variety of formats. Species' based
land management planning efforts must therefore depend upon general amphibian
references for habitat information. These references (see for example, Corkran
and Thoms 1996, Leonard et al. 1993, Nussbaum et al. 1983, Stebbins 1985) are
usually replete with microhabitat descriptions but are often lacking in landscape
level habitat descriptions. Therefore, modeling habitat relations for microhabitat
associates using macrohabitat information was considered a daunting challenge.
To meet the challenge, WAGAP established a Herp Committee consisting of academicians
and natural resource agency professionals. The Herp Committee started the data
collection process with a nationwide search for distribution data based on records
associated with voucher specimens available in herpetological collections. Since
most of these data were relatively old (pre-1960), batches of more recent field
inventory data were obtained and incorporated to the database. All data were reviewed
for reasonableness. In some instances, specimens were examined to assess the accuracy
of the identification. Field data that were not supported by voucher specimens
were accepted if trained and experienced scientists were involved in the data
collection. All of these data were used to create the best predicted vertebrate
distribution maps possible. We attempted to capture the available geographic precision
with expectations of conducting further analyses at a finer resolution
Landcover
WAGAP characterized the entire state by ecological zones and predominate vegetative
cover types (Cassidy, 1996). Sixteen scenes of 1991 Landsat Thematic Mapper (TM)
satellite imagery covering Washington State were spectrally clustered into approximately
200 classes per scene. The classes were grouped by similar spectral values and
areas of similar land cover types were delineated manually using the clustered
TM imagery as a backdrop. Each resulting land cover polygon was given a label
that included ecoregion, vegetation zone, and primary, secondary and tertiary
land cover and the proportion of each polygon by land
cover. An ecoregion is a contiguous geographic area of similar climate and
geological history. A vegetation zone is an
area in which moisture, temperature, elevation and other environmental parameters
combine to create conditions that favor similar vegetation communities.
The primary land cover is the actual land cover that occupies the greatest proportion
of the area in a polygon (e.g. closed canopy conifer forest or irrigated row-crop
agriculture). Secondary and tertiary land covers are actual land covers that occupy
the second and third greatest proportion of area in the polygon. Washington State's
land cover map consisted of approximately 15,000 land cover polygons. There were
1,865 unique combinations of ecoregion/vegetation zone/land cover (habitat) within
the State. Unique combinations of ecoregion and vegetation zone totaled 100.
Vertebrate Models
WAGAP vertebrate models were developed as matrices delineating ecoregion, vegetation
zone and land cover into core and peripheral zones on a species by species basis.
Core vegetation zones were identified by literature search, expert opinions and
known breeding occurrence. Core zones composed the range where species were most
commonly found. Peripheral zones were areas of infrequent occurrence where distribution
appeared to become uncharacteristically patchy. Often, these areas were at the
margins of a species' range limits.
The matrices also included a suitability code for each unique habitat combination.
The minimum mapping unit of Gap was 100 ha for terrestrial cover types and 40
ha for wetlands. Therefore, it was not possible to produce maps based on detection
of the microhabitats that amphibians are usually associated with.
The matrices were assigned codes indicating the suitability of the land cover
polygon. Polygons were labeled as not suitable, good, adequate, contingent upon
suitable habitats below the minimum mapping unit. The assignment of suitability
codes was obviously subjective and further study is needed to refine such a scheme.
Sampling Schemes
The combination of ecological vegetation zones and land cover types produces polygons
of similar character. The vertebrate models provide guidance for developing field
survey protocols appropriate for the fauna predicted to occur in the area to be
studied. We recommend that the WAGAP habitat characterization be used to develop
sampling schemes for both inventory and long-term monitoring of amphibians on
state and regional scales.
The WAGAP vertebrate models are well-suited for use in designing inventory and
monitoring. The amphibian models benefited from a baseline dataset of 10,631 records.
The Rana cascadae range model, for example, was based on 744 records
from 411 separate locations. These records spanned a 76 years of zoological collection
and observation (Dvornich et al, 1996). They clearly demonstrate an association
with higher elevation vegetation zones in the Cascades and Olympic Peninsula ecoregions.
Here, the species inhabits meadows, small ponds, and streamsides.
The vertebrate model for Rana
cascadae indicated which vegetation zones were likely to have populations
of this species. Table 1 illustrates the vegetation
zones selected within each ecoregion. The total number of habitats in each vegetation
zone were compared with the habitats selected. Each vegetation zone was identified
as core or peripheral. A total of 754 ecoregion/vegetation zone/habitat combinations
existed for the 6 ecoregions and 10 vegetation zones in Rana cascadae's
predicted distribution, and 438 were selected by the habitat model matrix A total
of 1,502 polygons were selected for its core habitat and 553 for peripheral. Inventory
and monitoring protocols employed in these vegetation zones should include techniques
known to be effective in detecting Rana cascadae and, for monitoring,
the techniques should be effective for assessments of population size or relative
abundance of the species.
A stratified random sampling scheme could be used to select polygons in which
monitoring sites and protocols could be established. Within the zones inhabited
by Rana cascadae, much of the land is roadless and very difficult to
access. In such zones, we recommend stratified random sampling to allow greater
sampling effort in the more accessible polygons. Stratified sampling should also
utilize information on the location of streams, emergent marshes, and small ponds
to ensure that polygons within these important habitats are well sampled.
It is our recommendation that inventory and monitoring programs treat each ecoregion/vegetation
zone as a separate entity. Within each zone sampling should be adequate for assessing
conditions throughout the zone. Field techniques should take advantage of WAGAP
range models to design field techniques capable of detecting and/or enumerating
all of the species predicted to occur in the zone.
Priorities for field inventories of ecoregion/vegetation zones are those zones
known or predicted to have rare or declining forms. Rana pretiosa, Rana pipiens,
Plethodon larselli, and Bufo woodhousei are well known for their
rarity or the extent of their declines. Bufo woodhousei is an example
of a species with a small predicted range which falls entirely within Rana
catesbeiana's predicted range. Few Bufo woodhousei populations are
known. For Bufo woodhousei, the WAGAP
database contained only 25 historical locations, though a study on the Hanford
Nuclear Reservation was responsible for adding most of the 42 new locations added
in 1996. Sampling of sites with known populations and sampling within ecoregion/vegetation
zones predicted to have Bufo woodhousei and other rare or declining species
should be considered a priority.
As alluded to in the previous paragraph, there are other considerations in establishing
the priorities for inventory and monitoring activities. One is to consider the
likelihood of continued range expansion of introduced species such as Rana
catesbeiana and to develop inventories that are able to track changes
in their ranges. Rana catesbeiana may play a role in the decline of other
amphibians. Predicting range was difficult for this species because field surveys
have not kept up with the natural and human-assisted range increases of this introduced
species. Additionally, the range of habitats used by Rana catesbeiana
(and many other amphibians) in Washington is imperfectly known. Because of the
suspected negative effects of Rana catesbeiana on native amphibians,
sampling of areas adjacent to the currently known range of this species should
be considered a priority.
Other Recommendations
It
became clear during the development of the vertebrate range models that improvement
of these models will be possible with finer scale habitat data as well as better
information on the attributes of suitable habitat for each species. At a coarse
scale, Dicamptodon copei, for instance,
can be assigned to streams within conifer forests. However, eventually, resource
inventories and more powerful computers will allow for distinctions between streams
of different sizes and substrate types as well as the already existing data that
allow us to model based on elevation, aspect, and slope. To better understand
how these features relate to the habitat needs of reptiles and amphibians, field
surveys should begin to measure and record these parameters.
We also recommend that observations from the general public, especially school
children, be included in amphibian inventory and monitoring programs. While the
public may not adhere to strict sampling protocols needed for rigorous statistical
analysis, their data will provide important information on the status and habitat
use of reptiles and amphibians. In the initial phases of a statewide NatureMapping
program utilizing school teachers and their students, sixty school children reported
Phrynosoma douglassii at locations known to them. These 60 locality records
represent more than what has been reported historically for this species and these
children have provided greater mapping precision and more detailed habitat information
than was available from most other data sources.
References
Cassidy, K.M., 1996. Land cover of Washington State, Volume 1. In K.M.
Cassidy, C.E. Grue, M.R. Smith, K.M. Dvornich, eds., Washington State Gap Analysis
- Final Report, Washington Cooperative Fish and Wildlife Research Unit, University
of Washington, Seattle, Volumes 1-5.
Corkran, C. C. and C. Thoms. 1996. Amphibians of Oregon, Washington, and British
Columbia - A field identification guide. Lone Pine publ. 175pp.
Dvornich, K.M., K.R. McAllister, and K.B. Aubry, 1996. Amphibians and Reptiles
of Washington State, Volume 2. In K.M. Cassidy, C.E. Grue, M.R. Smith,
K.M. Dvornich, eds., Washington State Gap Analysis - Final Report, Washington
Cooperative Fish and Wildlife Research Unit, University of Washington, Seattle,
Volumes 1-5.
Forest Ecosystem Management Assessment Group, 1993. Forest ecosystem management:
An ecological, economic and social assessment. Report of the Forest Ecosystem
Management Assessment Team, Chapter IV, 211 pp.
Leonard, W. P., H. A. Brown, L. L. C. Jones, K. R. McAllister, and R. M. Storm.
1993. Amphibians of Washington and Oregon. Seattle Audubon Soc. Seattle. 168pp.
Nussbaum, R. A., E. D. Brodie, and R. M. Storm. 1983. Amphibians and reptiles
of the Pacific Northwest. Univ. Press of Idaho, Moscow. 332pp.
Scott, J.M., F. Davis, B. Csuti, R. Noss, B. Butterfield, C. Groves, H. Anderson,
S. Caicco, F. D'Erchia, T.C. Edwards, Jr., J. Ulliman, and R.G. Wright, 1993.
Gap Analysis: A geographic approach to the protection of biological diversity,
Wildlife Monographs, 123:1-41.
Stebbins, R. C. 1985. A field guide to western reptiles and amphibians, 2nd
ed. Houghton Mifflin, Boston. 336pp.
U.S. Department of the Interior
U.S. Geological Survey
Patuxent Wildlife Research Center
Laurel, MD, USA 20708-4038
http://www.pwrc.usgs.gov/naamp3/naamp3.html
Contact: Sam Droege, email: Sam_Droege@usgs.gov
Last Modified: June 2002