Modeling the Competitive Dynamics Between

Native and Invasive Grasses Under Varying

Light Conditions

Presenters: Kristen Schultz and Ann Adams

Co-authors: Dr. Kelly Lyons and Dr. Eddy Kwessi

Trinity University, San Antonio

Integrated Research in Biomathematics (NSF)

Patterns in the Field

Patterns in the Field

Maintenance of biodiversity

Potential for restoration

Why are we interested in these

patterns?

What causes these patterns?

Coexistence can only occur when there is niche partitioning and

reduction in fitness difference between two species

What mechanisms allow invasive species to outcompete

native species?

Does light exposure affect the competition dynamics

between native and invasive grass species?

Overall Questions

Mathematical Modeling(Why we should care!)

The Model

Sensitivity Value

Sensitivity of a species to

interspecific competition

Growth rate of a species

in monoculture

Growth rate of a species in

interspecific competition

Growth rate of a species

in monoculture

₌₋

Competitive Dynamics: Niche Difference

Niche difference =Average effect of competition

on two competing species

AM1

Slide 10

AM1 not sure what to do in regards for putting words in the place of the equation symbolsAnn Marie, 10/7/2014

Competitive Dynamics: Relative Fitness

Difference

Relative Fitness

Difference

Variability in the effect

of competition on two

competing species=

Experimental Design

Focal native species: Sideoats grama (Bouteloua curtipendula) and little

bluestem (Schizachyrium scoparium)

Focal invasive species: King Ranch bluestem (Bothriochloa ischaemum)

Experimental Design

Sensitivity Value Calculation

KRSOG LBSKR

SOGKRKRLBS

Modeling Results

Competition

more likely!

One species

more likely to

outcompete

the other!

Modeling Results

One species

less likely to

outcompete

the other!Competition

less likely!

Conclusions

• KR competes less efficiently in low-light conditions

• SOG and LBS are more competitive in low-light

conditions

• Early facilitation may help SOG compete with KR

Why should we care?

• Focus native grass restoration efforts in

shaded areas

• SOG as staple species in restoration efforts

Acknowledgements

• Dr. James Shinkle and Dr. Jonathon King

• Austin Phillippe, Elizabeth Van Horn, Aaron

Skinner, Chris Robinson and Anh-Viet Dinh

• NSF and Integrated Research in

Biomathematics (IRBM)

QUESTIONS?