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3.0 Identification of Units for Management of Oahu Plant,
Snail, and Elepaio Populations
The identification of units for stabilization of plant populations for the Oahu Implementation
Plan (OIP) was based on the formula used by the Makua Implementation Team (MIT) for the
Makua Implementation Plan (MIP). However, for the OIP, preference was given to populations
within the action area (AA) in the Koolaus because of the reduced threat from military training to
these populations. Therefore, unlike the MIP some plant populations were favored for
stabilization inside the AA rather than attempting to capture a large geographic range across the
three stabilization populations of each species. Snail population units within the Koolau action
area were determined based on the knowledge of extant populations and the historical
geographical range of the species (see below). Genetic analyses may aid in determining the
number of populations to manage in order to capture the largest amount of genetic diversity for
the species (see Achatinella stabilization plans for genetic analyses underway). The Elepaio
population units were based on the knowledge of species and the currently occupied habitat.
Ideally, the Oahu Implementation Team (OIT) and the MIT would like to use a calculated
minimum viable population (MVP) size for each species for a measure of success of
stabilization. However, while determining the MVP for a given taxon is useful for measuring the
likelihood of success of different management actions in reaching stability, it was agreed that the
biological information needed to conduct such analyses is not available for the either the MIP or
the OIP target taxa. This is especially true for those taxa with extremely small populations in
highly degraded and fragmented habitats. In many cases, it is not clear how to define separate
populations, since this requires knowledge of mechanisms for gene flow within and between
populations for the different species, which can only be generally characterized at this point.
Throughout the MVP literature, it is stressed that demographic and environmental considerations
are of greater immediate concern than any population size criteria, and that management rather
than population size is more likely to increase the likelihood of population stability in the short
term. This means that stabilization should focus on the factors influencing rarity rather than a
minimum number of individuals. However, the IT recognizes that this type of data collection can
aid in the stabilization of the target taxa weather or not it is utilized for determining MVP sizes
(i.e. providing opportunities for: lifecycle study, effects of aboitic factors, and interactions with
other species) (Morris et al. 1999, Morris and Doak 2002). Therefore, data collection is
encouraged by the IT and MVP calculations for feasible species are a recommended
conservation measure of the Oahu Biological Opinion (USFWS 2003).
The major types of data needed are population size, demographic data (i.e. stage or age classes
and survivorship of individuals in each class), fecundity estimates (i.e. number of fruit/offspring
produced each year by each individual, in situ germination rates), soil seed bank estimates, etc.
The Army does not currently track all of this information but some of this information is
available for some species. In general population sizes are known for all target taxa, and some
fecundity estimates are known.
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Chapter 3.0 Identification of Units for Stabilization of Plant, Snail and Elepaio Populations
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Snail geographic units (GUs)
The Koolau Achatinella species have fewer individuals and populations and a much smaller
geographical range than Achatinella mustelina in the Waianae Mountains. Achatinella mustelina
management was addressed in the MIP, and the MIT determined that populations to be managed
for A. mustelina would be best determined by genetic analyses. However, due to the lack of
known individuals and populations for the Koolau Achatinella species, the OIT agreed to
population units based on known occurrences as most are very discrete and geographically
separated by several hundred meters. Therefore, all extant populations of A. byronnii, A. lila, and
A. livida will be managed for stability. The OIT determined that the known extant PUs of these
species are sufficiently disconnected from each other to be considered separate populations.
Alternatively, A. sowerbyana has a greater extant geographical range and larger number of
populations. For this reason the OIT recommended that population units be determined by
genetic analyses. Until the genetic analyses are completed the OIT has based PUs on geographic
occurrences, modeled after the A. mustelina ecologically significant units (ESU) from genetic
analyses conducted for the MIP (Holland and Hadfield 2002). The Koolau Achatinella species
were put into Geographic Units (GUs) until genetic analyses are completed (see individual
stabilization plans for more information).
Plant populations units (PUs)
For the Oahu plants, the OIP followed the basic population size criteria developed by the Hawaii
and Pacific Plants Recovery Coordinating Committee (HPPRCC 1994), the same criteria used in
the MIP (see paragraphs below).
Because biological populations are so difficult to define, the MIT defined population units (PUs)
as manageable geographic units of a given plant taxon. The term PU does not presume that the
group of plants interacts genetically and ecologically, as would a true population, but more
accurately describes a grouping of plants that may or may not be a viable population. PUs are
defined according to geographic separation, the presence of other probable barriers to gene flow
(such as ridges and habitat discontinuities), and limited likelihood of susceptibility to any given
threat event. Based on the current literature on gene flow for plants, little gene flow occurs
between individuals separated by over 500 meters, particularly for those taxa in which pollen
from one individual must be transferred to another individual for fertilization to occur (Ellstrand
et al. 1989). To err on the side of caution, the MIT doubled this distance, since we know so little
about the pollination mechanisms and gene flow of the target taxa. As a general guideline,
therefore, PUs are comprised of one or more individuals separated by 1,000 meters from
other individuals of the same taxon, or less if other factors, such as barriers to dispersal or
gene flow, are also present. Justifications describing the appropriate separating factors or
potential genetic affects on wild PUs are documented in each target taxon’s stabilization plans
for any PU that violates the 1,000 meter separation guideline.
The OIT assessed current and historic occurrences of the target plant taxa documented from
within the Oahu Training Areas and across the state of Hawaii, using the Hawaii Natural
Heritage Program database and the Oahu Army Natural Resources geodatabase. From these
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Chapter 3.0 Identification of Units for Stabilization of Plant, Snail and Elepaio Populations
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sources the OIT identified PUs known to be extant in 1983 (20 years prior to the USFWS 2003
BO).
Elepaio Population Units (PUs)
The population unit distinction for the Oahu elepaio appears easy to define compared to the plant
populations due to the disjointed extant populations and the unlikelihood of immigration and
emigration to and from the surrounding available habitat. There are six large populations and
several smaller remnant populations of Oahu elepaio. The smaller remnant populations generally
consist of males and are not expected to persist (VanderWerf 1998,1999, 2001, 2002, 2004). The
Army is required to conduct predator control on 75 breeding pairs per breading season rather
than protect a certain number of PUs (USFWS 2003). See elepaio threat control plan for a table
of the known populations of Oahu elepaio.
Selected Bibliography
Ellstrand, N. C., B. Devlin, and D. L. Marshall. 1989. Gene flow by pollen into small
populations: data from experimental and natural stands of wild radish. Proc. Nat. Acad. of Sci.
89(22): 9044-9047.
HPPRCC 1994: Hawaii and Pacific Plants Recovery Coordinating Committee. 1994. Minutes
of the July 7 and 8, 1994, meeting of the Hawaii and Pacific Plants Recovery Coordinating
Committee. Prepared for the U.S. Fish and Wildlife Service, Unpublished.
Holland, B. S. and M. G. Hadfield. 2002. Islands within an island: phylogeography and
conservation genetics of the endangered Hawaiian tree snails Achatinella mustelina. Molecular
Ecology 11: 365-375.
Morris, W.F. 1999. A Practical Handbook for Population Viablity Analysis. Copyright The
Nature Conservancy.
Morris, W.F., and D.F. Doak. 2003. Quantitative conservation biology: theory and practice of
population viability analysis. Sinauer Associates, Sunderland, Massachusetts, USA.
U.S. Army Garrison, Hawaii, Environmental Division, Directorate of Public Works. 1998b.
Biological assessment for programmatic section 7 consultation on routine military training at
Makua Military Reservation. Unpublished. 32 pp. + appendices.
U.S. Fish and Wildlife Service. 2003. Biological opinion of the U.S. Fish and Wildlife Service
for routine military training and transformation of the 2nd brigade 25th infantry division (light)
U.S. Army Installations Island of Oahu. Unpublished. 351 pp.
VanderWerft, E.A. 1998. Elepaio (Chasiempis sandwichensis). In The Birds of North America,
No. 344 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philidelphia, PA, and
the American Ornithologists’ Union, Washington, D.C.
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VanderWerft, E.A. 1999. Predator control, disease, and demography of the Oahu Elepaio. In
Hawaii Non-Game Management Program, Job Progress Report, 1 August 1998 through 31 July
1999. Division of Forestry and Wildlife, Hawaii. 18 pp.
VanderWerf, E.A. 2001. Control of introduced rodents decrease predation on artificial nests in
Oahu Elepaio habitat. Journal of Field Ornithology 72: 448-457.
VanderWerf, E.A. and D.G. Simith. 2002. Effects of alien rodent control on demography of the
Oahu Elepaio, an endangered Hawaiian forest bird. Pacific Conservation Biology 8:73-81.
VanderWerf, E.A. 2004. Demography of Hawaii Elepaio: variation with habitat disturbance and
population density. Ecology 85(3): 770-783.
VanderWerf, E.A. 2006. Distribution and Prevalance of Mosquito-Borne Diseases in Oahu
Elepaio. The Condor 108:770-777.
Final Oahu Implementation Plan 2008