A Poster Presentation delivered by Justin Tirrell at the Spring 2018 Biology Undergraduate Research Symposium at Utah State University

1. Introduction
Data simulations can reveal larger pictures about our
world. My program simulates the relationship between
Bruchid Beetles (predator) and Panama palm tree endocarps
(prey). By running simulations with parameters that match
the generation time and offspring count of my studied
populations, I can determine the effect of Beetle predation
on clumping patterns.
I chose to focus my simulations on Panama palm trees
because:
• The seeds retain scars from predation events, such as claw
marks and emergence holes.
• Data from endocarps is more reliable because it’s easier to
count and track all of the endocarps over multiple
generations.
• Significant study of palms in Panama has given enough
characterization about their predators to create complex
simulations.
I chose to use the Bruchid Beetles as predators because:
• They leave large emergence holes.
• Their generation time is the same as one season for
seedlings.
Simulating the Effect of Predator‐Prey Ratios on Clumping in
Seedling Distributions of Panama Palm Trees
Methods
My simulation features:
• Random generation of tree locations
• Offspring distributed with an inverse logarithmic
probability density curve
• Beetles taking Random Walks
• Multiple generations of Beetles and trees
• A function to recognize the strength of clumping
within a population
Results
I’ve developed the following skillsets:
• Programming in R statistical software
• Using Git Version control software
Hypothesis:
• I hypothesize that small Beetle‐seedling
ratios will not affect clumping, but large
ones will significantly reduce clumping.
Figure 2 – Simulations of Seed Dispersal
Figure 3 – Predation of
Endocarps by Bruchid Beetles
Figure 1‐ Versatile User Interface
Justin Tirrell
Utah State University
Biology
tirrelljustin95@gmail.com
Left: Coordinate plane showing the locations of trees, Beetles, Seeds, and Dead seeds.
Right: Data table representing the factors to be included in future models.
Program created using R Statistical Software
Abstract
Palm trees provide a unique opportunity to study what conditions optimize
the probability that a seed will grow successfully. The seeds of palm trees,
endocarps, are large and easy to locate. When they don't grow, predators
leave marks on them that tell the story of their fate. The focus of my
experiment is to determine how the current distribution pattern of parent
palm trees in Panama palm trees affects the future distribution of seedlings. I
have programmed a versatile model that takes the assumption that Bruchid
Beetles are the sole predators acting on the seeds, and that these fall from
the trees in an inverse logarithmic density pattern. The Beetles are
programmed to move to a random seed within an arbitrary distance of their
start point. If no seeds are near enough to them, then they starve. I
hypothesize that the Beetles will decrease clumping within five generations.1
Justin Tirrell, Eric Sodja, Cole Carlson, Noelle Beckman
Department of Biology, Utah State University.
Objectives
Simulations in R Statistical Software will determine:
• How the ratio of Bruchid Beetles to palm trees may be
expected to influence the distribution pattern of
mature palm trees in succeeding generations.
• How the initial distribution of palm trees may be
expected to influence the distribution pattern of
mature palm trees in succeeding generations.
Figure 3 Image Attributions:
“Attalea sp. , fruits and seeds” by Roger Culos
“Male Callosobruchus maculatus” by limbatus
“Attalea brasiliensis” by João Medeiros
Palm trees in Panama drop
large seeds called endocarps.
Bruchid Beetles lay their
eggs on the endocarps.
Beetle larvae prey on
the endocarps, leaving
large emergence holes
when mature.
User Interface: This simulation can take input from the user that describes the dynamics of the existing population.
Citations:
1. Wright, S. J. (1983). The Dispersion of Eggs by a Bruchid Beetle among Scheelea Palm Seeds and the Effect of Distance to the Parent Palm.
Ecology, 64(5), 1016–1021. https://doi.org/10.2307/1937808