Insect life history strategies in a changing world: the importance of integrating vital rates when evaluating life history trade-offs
Kerr, Natalie.
2019
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Living organisms are constantly making decisions about how to
optimize under variable and often unpredictable environments. As ecologists, we
are often interested in how these behaviors or traits of individuals scale up to
have consequences at the population-level. Here, I demonstrate the importance of
integrating demographic components throughout the life cycle to understand a
seemingly ... read moresub-optimal life history strategy in bumblebee colonies, to determine
how two congeneric butterflies may inform life history paradigms, and to evaluate
the consequences of a warming climate for a multivoltine butterfly species.
Bumblebees exhibit worker size polymorphism, yet most performance-based studies
have confirmed that larger workers are better at most tasks required for colony
functioning. Here, I used a cost:benefit analysis to reveal that the optimal
worker size matched the observed mean worker size in bumblebee colonies when
integrating across mechanistic elements of survival, resource return, and
production costs (Chapter 1). To date, my paper is the first study to integrate
multiple measurements of fitness to evaluate size-based tradeoffs in bumblebee
workers. Next, I integrated age-based larval (Chapter 2) and size-based worker
(Chapter 1) vital rates into integral projection models to evaluate the optimal
worker size distribution during colony growth and establishment. Using these
models to build hypothetical monomorphic and polymorphic colonies, I found that
the optimal mean matched the observed mean during colony establishment. During the
colony growth phase, however, I found that the optimal mean was higher than the
observed mean and the optimal variance was lower than the observed variance. I
hypothesize that bumblebee colonies might be adopting a combination of
conservative ("risk-avoidant") and diversifying ("risk-spreading") bet-hedging
strategies during the colony growth phase. Overall, I found a benefit to worker
size variation once I accounted for a proportion of workers within the colony are
required to conduct in-colony tasks. Next, I collected demographic data and built
age-based population models to evaluate life history trade-offs between these a
native and exotic butterfly species. I found that the patterns observed for these
two species corroborate the slow-fast life history paradigm. However, the exotic
species exhibits weakened trade-offs compared to the native species. These results
challenge fundamental life history theory that organisms should exhibit trade-offs
among vital functions, yet it supports the notion that these trade-offs may be
weaker for species in conditions that allow them to become invasive. Similarly,
these weakened trade-offs have only been reported for a couple of invasive plant
populations. Finally, I incorporated demographic components into commonly used
phenology models to predict the demographic consequences of phenological shifts in
a native multivoltine butterfly (Pieris oleracea) under a warming climate. I
predicted that populations in the southern limits of its range could add a fourth
generation with a warming climate resulting in a demographic bonanza. In the
northern ranges of its US distribution, this species may experience diametrically
opposed consequences where initial warming would expand the thermal window causing
a developmental trap followed by a demographic bonanza if warming continues. Here,
I provided a framework to incorporate demography into phenology models to evaluate
the consequences of a warming climate on multivoltine insects.
Thesis (Ph.D.)--Tufts University, 2019.
Submitted to the Dept. of Biology.
Advisor: Elizabeth Crone.
Committee: Colin Orians, Phil Starks, Michael Reed, Frances Chew, and Carol Boggs.
Keywords: Ecology, and Demography.read less - ID:
- zs25xn54b
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