Download lepidoptera larvae as an indicator of multi

LEPIDOPTERA LARVAE AS AN INDICATOR OF MULTI-TROPHIC LEVEL RESPONSES TO CHANGING SEASONALITY
IN THE ARCTIC
K. M. Daly,1 H. Steltzer,1 L. Gough, 2 M. Rich,2 C. Hendrix,2 N. Boelman,3 M. Weintraub,4
RESULTS
SEASONAL ABUNDANCE : SEASONALITY MANIPULATION &
SHRUB vs OPEN
6
IMVT - Pitfalls
ACCELERATED SNOWMELT
CONTROL
5
SDOT
IMVT
TLFS
ROMO
6
Snow p<0.06
METHODS:
We determined the abundance
of caterpillar larvae in relation
to the timing of snowmelt
through two approaches:
Total Larvae
Total Larvae
4
3
2
4
2
1
-14 - 0
0
150
160
170
180
1) A climate change
experiment in which we
accelerated snowmelt by 15
days through the use of
radiation-absorbing fabric and
warmed air and soil
temperatures using open-top
chambers, individually and in
combination with early
snowmelt treatment for each
of 5 replicate blocks.
15-28
29-42
43-56
57-70
Days Since Snow Free
Figure 3 : Total
seasonal abundance of
caterpillars caught
within pitfall traps in
both open and shrub
areas, summed across
the four transect sites.
As with Figure 2, day
0 represents when sites
were determined to be
100% snow free.
18
Control
IMVT Observations
Accelerated Snow Melt
Warmer Temperatures
Accelerated Snow Melt & Warmer Temperatures
Temp p <0.0004
Snow + Temp
p<0.0009
Shrub
Open
16
14
4
12
Total Larvae
Total Larvae
1-14
190
6
5
3
2
10
8
6
Snow p<0.07
Temp p<0.050
Snow + Temp p<0.0161
4
1
2
0
0
148-154
155-161
162-168
169-175
176-182
-14 - 0
183-189
1-14
Julian Day of Year
15-28
29-42
43-56
57-70
Days Since SnowFree
Figure 1 (above) : Total larvae observed in Summer 2011 within a moist acidic tussock tundra ecosystem at Imnavait Creek.
Pitfall traps (top) were only located in the control and early snowmelt plots. The experiment included control, early snowmelt,
increased temperature, and early snowmelt combined with increased temperature plots. Effects of early snowmelt, increased
temperature, sampling period and all their interactions were tested using a 3-way ANOVA. Significant and nearly significant
effects among treatment means are reported.
PARASITISM
0.6
22
12
Figure 4: Percent of parasitized larvae observed
within Imnavait Creek experiment: those caught in
pitfalls within the experiment, and averaged
between all open tundra and all shrub sites. The
number above each bar represents total amount of
larvae found in each method. Parasitism of
Lepidoptera larvae was identified as being by
braconid wasp and tachinid fly.
0.5
2) An observational 50 km
transect study with 4 sites that
naturally vary in the timing of
snowmelt.
% Parasitism
0.4
17
0.3
25
0.2
0.1
0.0
IMVT Observation IMVT Pitfall
•Caterpillar abundance was
determined by pitfall traps in all
study plots, and we also did
visual searches for caterpillars in
the climate change experiment.
OPEN Avg
SHRUB Avg
Method Comparisons
SEASONAL VARIATION IN PHENOTYPES
10
8
IMVT - Pitfall - caught
Hairy
Spiky
None
6
4
2
0
148-154
155-161
162-168
169-175
176-182
183-189
10
IMVT - Visual Observation
8
6
4
2
10
Figure 5 :
(left)
Seasonal
variations in
phenotypic
appearance
at Imnavait
Creek within
pitfall traps
(top) and
visual
observations
( bottom)
SHRUB
8
Hairy
Spiky
None
6
4
0
10
OPEN
8
6
4
2
0
0
148-154 155-161 162-168 169-175 176-182 183-189 190-196
Julian DOY
Figure 6 : Seasonal variations in
phenotypic appearance of larvae
within
Shrub (top) and Open (bottom)
habitats across the Dalton transect.
2
Total Larvae
OBJECTIVES OF STUDY:
-Quantify seasonal abundance of
caterpillars in relation to the timing of
•In
the
climate
change
snowmelt
experiment, observations began
-Evaluate the proportion of larvae that
one to three weeks after
host parasites.
snowmelt. In the transect study,
-Determine the timing of varying
observations began prior to when
phenotypes of larvae (hairy, spiky, or study sites were completely snow
smooth-skinned)
free.
Figure 2 : Seasonal
abundance of larvae
from Day 0 – the date
that each site was
averaged to be 100%
Snow free. The
transect sites span a
total distance of 50 km
along the Dalton
Highway in the North
Slope of Alaska.
0
Total Larvae
INTRODUCTION
Earlier snowmelt and warming
temperatures in the Arctic will
impact multiple trophic levels
through the advancement in
latitude of shrub vegetation and
the timing and availability of food
resources for animals.
Lepidoptera are a vital link within
the Arctic ecosystem; their roles
include pollinator, parasitized
host for other pollinating insects,
and essential food source for
migrating birds and their
fledglings.
HYPOTHESIS
Seasonal climate patterns affect total
abundances of caterpillars in the
Arctic. In response to changes in
seasonality, including earlier
snowmelt and warming, we expect
caterpillar abundance to increase.
Shrub-dominated landscapes
generally melt later than open tundra,
so we expect that caterpillar
abundance will be higher in open
tundra. We expect that caterpillars in
moist acidic tundra are hosts to one
or more pollinators. It is expected
that larvae with thickest skin-type
(hairy) will appear earliest.
SUMMARY / DISCUSSION:
Lepidoptera larvae appear to exhibit drastic variation
in seasonal abundance:
• Where snowmelt was experimentally accelerated
and temperatures were warmed, caterpillar
abundance was greatest and more were seen earlier
in June.
• Within the transect study, we observed two seasonal
peaks in caterpillar abundance. One occurs within
two weeks of snowmelt and one occurs four to six
weeks following snowmelt at all four sites.
Shrub vegetation is increasing in the Arctic as
temperatures warm. Vegetation differences may
influence Lepidoptera larvae abundance:
• Throughout the season, more caterpillars were
continuously found in open tundra plots compared
to shrub plots.
Lepidoptera serve an essential role as parasitized host
to other pollinating insects:
•Proportion of parasitism was up to 54% of the
observed animals and was greatest for caterpillars
observed visually in the climate change experiment
compared to those observed in pitfall traps in the
experiment and across the transect.
-14 - 0
1-14
15-28
29-42
43-56
Days Since 100 % Snow Free
57-70
Larvae were classified as being hairy,
spiky, or smooth skinned. This method
of classification was chosen because
species identification (through raising
larvae to adulthood) was not possible
due to the constraints of each method:
observations occurred within the
established climate manipulation
experiment where larvae could not be
removed, and the pitfall method is
lethal.
Seasonal emergence of larvae phenotypes may be
linked to temperature:
•In both studies, we found that caterpillars found soon
after snowmelt were hairy or spiky, while caterpillars
with smooth , not spiked/hairy skin were most
abundant later in the season.
ACKNOWLEDGEMENTS:
•
Grant to Boelman: National Science Foundation REU Grant ARC-0908444 SUP
•
Grant to Steltzer: National Science Foundation NSF-OPP Grant # 1007672
•
Grant to Daly: Fort Lewis College Natural Behavioral Sciences Grant
•
contact [email protected]
RESEARCH TEAM :
1. Department of Biology, Fort Lewis College, Durango CO
2. Department of Biology, University of Texas at Arlington, TX
3. Lamont-Doherty Earth Observatory, Columbia University, New York City, NY
4. Department of Environmental Science, University of Toledo, OH.