Download Wildland Impacts of Exotic Wildlife

Wildland Impacts of
Invasive Wildlife
Natalie B. Gates, D.V.M.
Wildlife Biologist
National Park Service
Point Reyes National Seashore
Wildland Impacts of Invasive
Wildlife
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Definitions
What we know about invasive wildlife
Case studies in Marin
Future considerations
Definitions
non-native species
introduced species
exotic species
non-indigenous species
alien species
transplants
„species of plants and
animals that are not native
(natural) to an area
„species that did not evolve
with the ecosystem in
which they are found
„the result of deliberate or
accidental human activities
Definitions
invasive species
species whose
introduction causes or is
likely to cause economic or
environmental harm or
harm to human health
„ non-native species whose
introduction and/or spread
threatens biological
diversity
„ agents of change
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Definitions
All invasive species are non-native.
Not all non-native species are invasive.
What we know about invasive
wildlife
The impacts of alien
invasive species are
immense, insidious, and
usually irreversible. They
may be as damaging to
native species and
ecosystems on a global
scale as the loss and
degradation of habitats.
(World Conservation
Union, IUCN)
What we know about invasive
wildlife
Hundreds of
extinctions
have been
caused by alien
invasives.
(IUCN)
What we know about invasive
wildlife
In the past 40 years, the
rate of biotic invasion has
increased enormously
because of human
population growth, rapid
movement of people, and
alteration of the
environment.
What we know about invasive
wildlife
Most vertebrate invaders have a
close association with humans,
as well as high abundance in
their native range, broad diet,
short generation times, ability of
females to colonize alone, and
ability to function in a wide
range of physical conditions.
(Ehrlich 1989)
Case studies in Marin
(Not a complete cataloguing of all invasive wildlife species in
Marin)
Not discussed:
Non-Native Bees
Bullfrogs
Brown-headed Cowbirds
Starlings
Rock Pigeons
English Sparrows
Black Rats
House Mice
Introduced Game Fish
Virginia Opossum
ETC……
Case studies in Marin – mosquitofish
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native to S. America
distributed by many mosquito
control programs / homeowners
some introductions to natural areas
are inadvertent (flooding,
overflow)
mosquitofish have become
established in Marin’s perennial
streams/ponds
impacts in California:
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prey heavily on frog eggs, treefrog
tadpoles (Goodsell and Kats 1999)
prey on California newts
(Gamradt and Kats 1996) even
when high densities of mosquito
larvae were presented as
alternative prey
thought to be cause of declining
frog numbers in Australia (Webb
and Joss 1997)
Case studies in Marin – wild turkeys
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native to U.S. east of the Rocky
Mountains
Rio Grande subspecies introduced
for hunting to Marin in 1970s –
populations increasing
broods of 10-12 poults -population
should be capable of a five-fold
increase in years with abundant
food (Barrett & Kucera 2005)
heavy use of oak mast at PORE
impacts in Marin/Sonoma:
(Gluesenkamp, in press)
„ ↑ soil disturbance
„ ↑ acorn removal
„ ↓ invertebrates
(crickets,spiders,ants)
Case studies in Marin – wild turkeys
Case studies in Marin – cats
cats arrived in N.A. with first
colonists
„ > 60 million in N.A (Nassar
& Mosier 1991)
„ 50 million feral cats (PAWS
1997)
„ diet (outdoor access) =
mammals, birds, reptiles
„ rural areas: approx. 60% of
households have cats (Ogan
and Jurek 1997)
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Case studies in Marin – cats
ƒ in VA and WI each feral
cat killed approx. 5
birds/year (Luoma 1997 )
ƒ pet cats kill a similar
number of birds as feral cats
(McKay 1996)
1996
ƒ 465 million birds are killed
by cats per year
ƒ impacts in EBRParks:
(Hawkins, 1998):
ƒ↓ birds (50%)
ƒ↓ native mice, ↑nonnative mice
Case studies in Marin – wild pigs
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NPS
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R. Saulino
feral pigs, wild boar and hybrids
native to Eurasia and N. Africa
use oak mast heavily
populations can increase rapidly with 2
farrowings/year and 4-7 piglets/litter
Marin introduction 1975-1978.
peak 1984 - last confirmed Marin
sighting 1994
Impacts in California:
„ damage tree seedlings and limit
tree regeneration (Sweitzer &Van
Vuren 2002)
„ enhance spread of invasive weeds
(Kotanen 1995)
„ compete with native species for
food resources (Gomez et al.
2003)
„ 2-3 X ↑ erosion (MMWD 1987)
Case studies in Marin – wild pigs
Case studies in Marin – European
fallow deer
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native to N. Africa and Asia
Minor
introduced to West Marin for
hunting in the 1940s and
1950s
Impacts (Marin):
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dietary overlap with native
species (Elliott 1983)
carry diseases known to affect
native deer (Riemann et al
1976)
denudation of woodlands and
riparian areas (Fellers &
Osbourn 2006)
(Bildfell et al 2004)
Case studies in Marin – European
fallow deer
Future considerations
Future considerations – invasional
meltdown
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some initially benign introductions
may occasionally turn into
damaging invasions
positive interactions among the
hundreds of introduced species
green crabs in CA selectively prey
on native clams, causing an
increase in non-native clams
(previously suppressed by
competition) (Grosholtz 2005*)
crazy ants extirpate the native red
land crab on Pacific islands
eventually leading to leading to
canopy dieback and even deaths of
canopy trees (O’Dowd et al 2003)
Future considerations – climate
change
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Expected CA changes:
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Characteristics of good invaders may
favor them in changing times
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altered fire regimes
flooding
prolonged drought cycles
altered vegetation
broad diet
short generation times
ability of females to colonize alone
ability to function in a wide range of
physical conditions
"Some exotic species that now are not
quite invasive could be pushed over
that threshold to become invasive
simply because they're able to keep up
with the climate." (Weis, UC Irvine*
Irvine )
Future considerations - Sudden Oak
Death
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Tanoaks
Important for:
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Birds
Rodents (woodrats)
Deer
(USDA/USFS)
(Horton & Wright 1944)
Future considerations – human
population
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↑ risk new
introductions
reduced, fragmented
habitat
↑ demand for water
and recreation