climate change effects on predator/prey interactions: how can we ...

CLIMATE CHANGE EFFECTS ON PREDATOR/ PREY
INTERACTIONS: How can we conserve persistence and
resilience in a murky sea of idiosyncrasy

Global <strong>climate</strong> <strong>change</strong>
• What is changing
• Can we relate GLOBAL <strong>change</strong> patterns
to LOCAL systems
– Landscape variables measured at broad scale
– animals usually measured at local scale
Everything is connected so at some
point Natural Selection should elicit
a response in… everything.

Mean monthly minimum temperature: Yosemite
Valley, CA 1905 - 2007
Loss of 3
freezing
months
(Nov,
Mar, Apr)
Moritz et al. 2008; Western regional <strong>climate</strong> center
Leading to:
• Higher variability in annual snowpack
• Earlier snow melt
• Decreased stream flows

Research on <strong>effects</strong> of <strong>climate</strong> <strong>change</strong>
Models worldwide attempt to model animal distributions on
predicted habitat maps
Predictions:
1. Few species go extinct
a. unsuitable conditions for persistence
b. out competed by invading/pioneering species
2. Many species will dramatically contract in distribution
a. increased fragmentation
b. reduced resilience in population dynamics (more vulnerable to
extinction with perturbations)
3. Others will extend their range
a. usually at the expense of another species (e.g. the alpine
chipmunk being displaced by lodgepole chipmunk)
Community composition is going to <strong>change</strong>

Animals adapt on a species level
Summary of Grinnell resampling small
mammal survey (Moritz et al. 2008)
Range
Expansion
Range
Contraction
No Change
Number of
species
3 spp Higher
2 spp Lower
6 spp Higher
1 spp Lower
12 spp
1 spp Both
2 spp Both
• No pattern or mechanism as to who’s range contracted or expanded
• Each small mammal guild is represented in all categories
• ALL of these species are important prey items in the Sierra Nevada

Conflicting results in Sierra Nevada
Within Genus (Neotoma spp.; Moritz et al. 2008)
• Large-eared woodrat showed no <strong>change</strong>
in distribution from 1920 to 2005
• Bushy-tailed woodrat showed significant
<strong>change</strong>
Within Species (bushy-tailed woodrat)
• One study showed range expansion (East slope:
McDonald and Brown 1992)
• Another study showed range contraction (West
slope: Moritz et al. 2008)

Idiosyncrasy in our thinking and our data
Conflicting paradigms
1. Ambient temperature and animal physiological
constraints influence species susceptibility to
extinction (McDonald and Brown 1992)
• True for species constrained in distribution, e.g. high
montane mammals
2. Animal distributions influenced by habitat <strong>change</strong>s
not physiological constraints (Johnston and Schmitz 1997, Moritz et al. 2008)
• Habitat quality directly linked to population dynamics for
herbivores, aka PREY
• Prey population dynamics highly correlated to predator
population dynamics

Classic predator-prey population cycles: snowshoe
hare and Canada lynx
Trapping records from Hudson Bay, Canada
Highly correlated connections in the predator-prey system
- If something happens to one, it throws off the other
- amplitude variability is positively related to probability of
extinction

Prey population cyclicity
Cyclicity = amplitude and frequency of cycles
• Increases with latitude and snow cover.
• Decreases with generalist predators
• Increases with specialist predators
• Prey food source reliability related to prey
cyclicity (e.g. acorn crops cycle)

Spotted owl prey annual abundance patterns
120
100
flying squirrel
deer mouse
Prey abundance
80
60
40
20
Rosenberg et al. 2003
0
1986 1988 1990 1992 1994 1996 1998
Year

Prey abundance and owl reproductive success
Prey abundance
120
100
80
60
40
20
flying squirrel
deer mouse
spotted owl reproduction
2.0
1.5
1.0
0.5
# of owlets / owl pair
0
Rosenberg et al. 2003
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996
Year
0.0

northern goshawk
barred owl
(invader)
great horned owl
raven
Spotted owl
Habitat and diet
SPECIALISTS
passerine birds
shrews
bats
flying squirrel
deer mice
chipmunks
seeds
grasses
woodrats
forbs
voles
pollen
beetles
moths
insects
lichen
fungi
trees
detritus
shrubs
leaves

Spotted Owl Diets: Yosemite
Woodrat = also important prey species
Flying
squirrels
Woodrats
Closed canopy
Open canopy

Flying squirrel response to <strong>climate</strong> <strong>change</strong>:
1. If forest dries out, flying squirrels follow truffles confined
to riparian areas due to their prey’s (truffles) association
with high soil moisture
2. Predators of flying squirrels follow prey to riparian areas
3. Connectivity to prey refuge areas, high prey abundance
areas, and predator refuge areas
- Will they cross non-habitat patches
4. Will predator survival decline

How does idiosyncratic prey response
affect the predator
• All woodrats equally preferred prey
• Predator (spotted owls) inhabitat a gradient of
particular habitat structure (e.g., late seral forest)
• Owls in one habitat (100 – 85% canopy closure) may
have declining woodrats (species that prefer
closed canopy) while owls in another habitat (70
– 60 % closure) see little <strong>change</strong> in woodrats
(those that prefer open forest).
Bushytailed
woodrat
Big-eared
woodrat

How can we manage for spatial
idiosyncrasy
Prey and Predators need access to a
mosaic of habitat types
– habitat patches need to contain desired
structure
– Must be connectivity between patches
• Many species may not cross what they perceive
as non-habitat despite the size of the nonhabitat
patch
• Conservation areas may need to expand or
reassess their borders to meet these habitat
shifts

ADAPTIVE RESEARCH
WORK TOGETHER
• With no clear patterns of biological responses
to <strong>climate</strong> <strong>change</strong>
• Apply general framework for approaching
research
– Change focus as new information arises
• Integrate different sciences may be
important in obtaining the answers we need
to guide adaptive management policies

Adaptive Research Framework
1. Prioritize species of concern (e.g., Ecology)
a. Pika are habitat specialists and they can’t escape to
higher ground!
- vulnerable montane mammals if temperatures increase the
predicted 3 0 C (McDonald and Brown 1992)
b. Keystone consumer: Pika influence alpine plant
composition, reduce inter-specific competition in
plants
c. Many predators consume pikas
d. Loss of pika leads to trophic cascades

Adaptive Research Framework
2. Prioritize mechanisms of <strong>change</strong>
affecting species (Physiology and botany)
a. Pika are limited in physiological ability to deal
with heat
- Increased temps reduce foraging times
b. Reduced snow pack <strong>change</strong> plant composition
- Plant community pika not evolved to exploit
c. Lack of livestock grazing associated with higher
probability of local persistence (Beever et al. 2003)

Adaptive Research Framework
3. Identify habitat features resilient or
resistant to <strong>change</strong> (Geology)
a. Rock glaciers and rock-ice features
• Interstitial micro<strong>climate</strong> remains cool in summer
(Delaloye and Lambiel 2005)
• Pika refuge with disappearing snow patches (Millar et
al. 2007)
Rock glacier

Salient points
GIVE ANIMALS ROOM TO ROAM
As habitat <strong>change</strong>s:
Prey need to find
suitable habitat and
the predators need to
find prey as they are
seeking shifting
habitats

Salient points
ADAPTIVE RESEARCH
Integrate different sciences:
knowledge diversity is important in obtaining
the answers we need to guide adaptive
management policies