The Effect of Salinity on Predator-Prey
Dynamics in a Marine System
Kathryn Blackley, Alexander Looi,
David Rosenberg
Cornell University
Department of Ecology and Evolutionary Biology
Our Research Question
• What are the effects of an abiotic influence
on predator-prey dynamics?
• Especially if the abiotic factor has different
effects on predator and prey
– Tested salinity as an abiotic factor
N
Nitrogen
Schaffner
Prey
Resource:
Nitrogen
Prey:
Chlorella
autotrophica
Predator:
Brachionus
plicatilis
Approach to answering our question
• Conducted a growth rate experiment to
determine effects of the abiotic factor
• Conducted experiments using chemostats at
different salinities
– Used an existing mathematical model to describe
our system
Approach to answering our question
• Conducted a growth rate experiment to
determine effects of the abiotic factor
• Conducted experiments using chemostats at
different salinities
• Used an existing mathematical model to
describe our system
Growth rate (day-1)
Salinity affects
rotifers more than it does algae
Salinity (g/L)
Approach to answering our question
• Conducted a growth rate experiment to
determine effects of the abiotic factor
• Conducted experiments using chemostats at
different salinities
• Used an existing mathematical model to
describe our system
Dynamics are affected by salinity
Experimental Data (rep. 2)
Days
Days
Rotifers / mL
Algal cells / mL
Experimental Data (rep. 1)
Approach to answering our question
• Conducted a growth rate experiment to
determine effects of the abiotic factor
• Conducted experiments using chemostats at
different salinities
• Used an existing mathematical model to
describe our system
Important parameters in our model
are birth rate and death rate
Change in Nitrogen
(Prey resource)
abundance
Change in
Algae (Prey)
abundance
Change in Rotifer
(Predator)
abundance
Fussmann et al. 2000
Dynamics are affected by salinity
Experimental Data (rep. 1)
Rotifers / mL
Algal cells / mL
Model Results
Days
Days
Dynamics are affected by salinity
Experimental Data (rep. 2)
Days
Days
Rotifers / mL
Algal cells / mL
Model Results
How is salinity affecting this system?
• What parts of birth and death are affected?
– Used model data to make inferences about rotifer
life history as a function of salinity
• Could salinity be affecting egg development
time and/or egg viability?
• Conducted our own experiment using the
Edmondson egg ratio method
Rotifer egg viability and development time
are more effected at higher salinities
New Modified Model
Change in Nitrogen
(Prey resource)
abundance
Change in
Algae (Prey)
abundance
Change in Egg
(Predator)
abundance
Change in Rotifer
(Predator)
abundance
𝒅𝑵
𝜷 𝑪 𝝌𝑪 𝑵
= 𝜹 𝑵𝒊 − 𝑵 −
𝑪
𝒅𝒕
𝑲𝑪 + 𝑵
𝒅𝑪
𝜷𝑪 𝑵
𝝆𝑹 𝑪
=
𝑪−
𝑹 − 𝜹𝑪
𝒅𝒕 𝑲𝑪 + 𝑵
𝑲𝑹 + 𝑪
𝒅𝑬
𝜷𝑹 𝑪
𝟏
=
𝑹− 𝜹+ 𝑬
𝒅𝒕 𝑲𝑹 + 𝑪
𝝉
𝒅𝑹
𝑬
= 𝑺𝑬 − 𝜹 + 𝒎 𝑹
𝒅𝒕
𝝉
New Parameters:
𝑺𝑬 = Egg viability 𝝉 = Egg development time
Current situation
• Our current modified model works better
– For B. plicatilis:
• Working to obtain carbon content
• Have obtained values for assimilation efficiency
• Functional response of B. plicatilis might be
type III instead of type II
Acknowledgements
• Teppo
Questions and Suggestions?