Trait Hierarchies and Spider Foraging - A Tail of Two Webs

Spiders are a very large, diverse, and ecologically important set of predators in both agricultural and
unmanaged terrestrial ecosystems. They have been estimated to consume 400 - 800 million metric
tons of biomass globally - around 1% of global net primary production (Nyffeler and Birkhofer, 2017).
Yet, the effects of land-use and climate change on spider populations and the knock on effects on
biomass flows and stability of terrestrial food webs remain poorly understood. To understand the role
of spiders in biomass flows through ecosystems, we must first understand their foraging behaviours
and limits on their consumption rates.
When modelling biological data from a traits-focused approach, we often derive unmeasured or
unmeasurable values from those we can measure (e.g. when deriving the consumption rate of an
animal, we can use a model which considers search rate and attack success to infer consumption
rate). These links between traits are often hard to disentangle and quantify, however given a robust
hierarchical framework, we can extract information about trait interdependence from the topology of
the network. A difference in this topology, or the parameters of the models which link traits together
can indicate differential strategies or adaptations are at play, owever, the tools to perform this
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analysis are underdeveloped and their use remains untested. Thus, developing the tools to enable
efficient evaluation of trait networks is a critical task which will open up this approach for use
throughout trait-based ecology.
In this project, I will use a hierarchical approach to biological traits to evaluate and understand
changes in spider web architecture along multiple axes of variation. I will then combine metabolic and
foraging theories to build mathematical models for the scaling of foraging rates of spiders with body
mass under under varying environmental temperatures. This is only now possible because of recent
advances at the interface of the Metabolic Theory of Ecology and Foraging Theory (Pawar et al. 2012,
Dell et al. 2014, Rizzuto et al. 2018).
Specifically, I aim to:
1. Formalise and develop a hierarchical framework to aid in evaluation of the relationships between
linked biological traits, which will have broad applications beyond the application to spiders.
2. Apply this framework to spider foraging and web traits to:
- Evaluate the effect of temperature shifts on web design choices (e.g., the mathematical scaling of
web size with body mass) made by spiders in different environments (e.g., agricultural vs. forested
landscapes).
- Evaluate the cost tradeoff involved in web building in three (aerial) vs two (ground) spatial
dimensions.
3. Validate model predictions from my previous mechanistic model of spider forging and refine this
modelling by aggregating existing data and collecting new laboratory and field data on metabolic and
foraging rates of representative groups of spiders.
4. Use the consumption/foraging rate models to estimate energy fluxes in different types of terrestrial
foodwebs in both agricultural and natural landscapes.