Table Of ContentThe Changing Structure and Function of Arthropod Food Webs
in a Warming Arctic
by
Amanda May Koltz
University Program in Ecology
Duke University
Date:_______________________
Approved:
___________________________
Justin Wright, Supervisor
___________________________
William Morris, Chair
___________________________
Dean Urban
___________________________
Robert Dunn
Dissertation submitted in partial fulfillment of
the requirements for the degree of Doctor of Philosophy
in the Program in Ecology in the Graduate School of
Duke University
2015
i
v
ABSTRACT
The Changing Structure and Function of Arthropod Food Webs
in a Warming Arctic
by
Amanda May Koltz
University Program in Ecology
Duke University
Date:_______________________
Approved:
___________________________
Justin Wright, Supervisor
___________________________
William Morris, Chair
___________________________
Dean Urban
___________________________
Robert Dunn
An abstract of a dissertation submitted in partial
fulfillment of the requirements for the degree
of Doctor of Philosophy in the Program in Ecology
in the Graduate School of
Duke University
2015
i
v
Copyright by
Amanda May Koltz
2015
Abstract
Environmental changes, such as climate change, can have differential effects on
species, with important consequences for community structure and ultimately, for
ecosystem functioning. In the Arctic, where ecosystems are experiencing warming at
twice the rate as elsewhere, these effects are expected to be particularly strong. A proper
characterization of the link between warming and biotic interactions in these particular
communities is of global importance because the tundra’s permafrost stores a vast
amount of carbon that could be released through decomposition as greenhouse gases
and alter the global rate of climate change. In this dissertation, I examine how arthropod
communities are responding to warming in the Arctic and how these responses might be
affecting ecosystem functioning.
I first address the question of whether and how long-‐‑term changes in climate are
affecting individual groups and overall community structure in a high-‐‑arctic arthropod
food web. I find that increasingly warm springs and summers between 1996-‐‑2011
differentially affected some arthropod groups and that this led to major changes in the
relative abundances of different trophic groups within the arthropod community.
Specifically, spring and summer warming are associated with higher absolute
abundances of herbivores and parasitoids and lower relative abundances of detritivores
within the community. These changes are particularly pronounced in heath sites,
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suggesting that arthropod communities in dry habitats are more responsive to climate
change than those in wet habitats. I also show that herbivores and parasitoids are
sensitive to conditions at subzero temperatures, even during periods of diapause, and
that all trophic groups benefit from a longer transition period between summer and
winter. These results suggest that the projected winter and springtime warming in
Greenland may have unexpected consequences for northern arthropod communities.
Moreover, the relative increase in herbivores and loss of detritivores may be changing
the influence of the arthropod community over key ecosystem processes such as
decomposition, nutrient cycling, and primary productivity in the tundra.
Predator-‐‑induced trophic cascades have been shown to impact both community
structure and ecosystem processes, yet it is unclear how climate change may exacerbate
or dampen predator effects on ecosystems. In the second chapter of my dissertation, I
investigate the role of one of the dominant tundra predators within the arctic ecosystem,
wolf spiders, and how their impact might be changing with warming. Using results
from a two-‐‑year-‐‑long field experiment, I test the influence of wolf spider density over
the structure of soil microarthropod communities and decomposition rates under both
ambient and artificially warmed temperatures. I find that predator effects on soil
microarthropods change in response to warming and that these changes translate into
context-‐‑specific indirect effects of predators on decomposition. Specifically, while high
densities of wolf spiders lead to faster decomposition rates at ambient temperatures,
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they are associated with slower decomposition rates in experimentally warmed plots.
My results suggest that if warming causes an increase in arctic wolf spider densities,
these spiders may buffer the rate at which the massive pool of stored carbon is lost from
the tundra.
Wolf spiders in the Arctic are expected to become larger with warming, but it is
unclear how this change in body size will affect spider populations or the role of wolf
spiders within arctic food webs. In the third chapter of my dissertation, I explore wolf
spider population structure and juvenile recruitment at three sites of the Alaskan Arctic
that naturally differ in mean spider body size. I find that there are fewer juveniles in
sites where female body sizes are larger and that this pattern is likely driven by a size-‐‑
related increase in the rate of intraspecific cannibalism. These findings suggest that
across the tundra landscape, there is substantial variation in the population structure
and trophic position of wolf spiders, which is driven by differences in female spider
body sizes.
Overall, this dissertation demonstrates that arctic arthropod communities are
changing as a result of warming. In the long-‐‑term, warming is causing a shift in
arthropod community structure that is likely altering the functional role of these animals
within the ecosystem. However even in the short-‐‑term, warming can alter species
interactions and community structure, with important consequences for ecosystem
function. Arthropods are not typically considered to be major players in arctic
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ecosystems, but I provide evidence that this assumption should be questioned.
Considering that they are the largest source of animal biomass across much of the
tundra, it is likely that their activities have important consequences for regional and
global carbon dynamics.
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Dedication
This dissertation is dedicated to my parents, stepparents, and husband.
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Contents
Abstract .......................................................................................................................................... iv
List of Tables ................................................................................................................................ xii
List of Figures ............................................................................................................................. xiv
Acknowledgements ................................................................................................................... xvi
1. Introduction ............................................................................................................................... 1
1.1 Species and community responses to climate change ................................................. 1
1.2 Ecological consequences of climate change in the Arctic ........................................... 1
1.3 Arthropods as a model system for understanding effects of climate change on
biological communities .......................................................................................................... 3
1.4 Objectives ........................................................................................................................... 5
2. Differential response to climate change among arthropods is altering the structure of
arctic communities ........................................................................................................................ 7
2.1 Introduction ....................................................................................................................... 7
2.2 Methods ........................................................................................................................... 11
2.2.1 Study sites ................................................................................................................... 11
2.2.2 Climate data ............................................................................................................... 11
2.2.3 Arthropod data collection ........................................................................................ 12
2.2.4 Analyses ...................................................................................................................... 15
2.3 Results .............................................................................................................................. 16
2.3.1 Climate change over the study period ................................................................... 16
2.3.2 Links between arthropod abundances and environmental predictors ............. 18
ix
2.3.3 Links between variability in community structure and environmental
predictors ............................................................................................................................. 18
2.4 Discussion ........................................................................................................................ 25
3. Predator effects on a soil food web can buffer carbon losses in a warmer Arctic ......... 31
3.1 Introduction ..................................................................................................................... 31
3.2 Methods ........................................................................................................................... 34
3.2.1 Experimental design ................................................................................................. 34
3.2.2 Measures of community structure and function .................................................. 36
3.2.2.1 Sampling the surface and belowground community ................................... 37
3.2.2.2 Decomposition .................................................................................................... 37
3.2.2.3 Soil moisture ....................................................................................................... 38
3.2.3 Statistical analyses ..................................................................................................... 38
3.3 Results .............................................................................................................................. 39
3.3.1 Effects of wolf spider density and temperature on microarthropods ............... 39
3.3.2 Effects of wolf spider density and temperature on decomposition ................... 41
3.4 Discussion ........................................................................................................................ 44
4. Larger female body sizes lead to increased cannibalism rather than higher recruitment
in arctic wolf spiders ................................................................................................................... 50
4.1 Summary .......................................................................................................................... 50
4.2 Results and discussion ................................................................................................... 52
4.3 Methods ........................................................................................................................... 61
4.3.1 Field sampling ............................................................................................................ 61
4.3.2 Sample processing ..................................................................................................... 63
x
Description:Arthropods are not typically considered to be major players in arctic scores to habitat type and the composite climate parameters with Vegan's
