2025-04-23

Introduction

→ Freshwater Salinization is a phenomena threatening systems globally.

  • Increase in salt content in a body of water through environmental and anthropogenic means:
    • Evaporation
    • Sea level rise
    • Storm Surge
    • Land subsidence
    • and more…

Introduction - Knowledge Gaps

  • Increased salt content creates osomoregulatory stress
  • However the degree of stress varies between organisms
  • This skew in tolerance can alter trophic intreactions… but we don’t really know!
  • Exacerbated by understudied organisms

Hypotheses

**Figure 2.** Logical diagram of food web hypotheses.

Figure 2. Logical diagram of food web hypotheses.

Methods

  • 15 mesocosms in a randomized block design
    • 0.4 ppt, 3 ppt, 5 ppt treatments
    • Four enclosures with randomized predator presence and grazer density

  • Experimental community of:
    • Hyla cinerea tadpoles
    • Erythemis simplicicolis naiads
    • Algae and zooplankton inoculation

Methods

  • Sampling of every trophic group every two weeks across a period of five months
  • Additional water quality data (temp, pH, DO, etc.)

★ Not all variables are not fully implemented at this stage of data analysis

Methods

  • Structural Equation modeling (pSEM) for trophic analysis
    • Use of mixed effects linear models with temporally autocorrelated data
    • Warning: This package breaks a lot
  • Proportional Hazards modeling (coxph) for time-to-event analysis for metamorphosis
    • Co-opted survival analysis

A quick assumption check

##                       Estimate Std. Error t value Pr(>|t|)
## (Intercept)               2.45       0.05   51.32     0.00
## Wet.Weight..g.           -0.16       0.04   -4.47     0.00
## as.factor(Treatment)3     0.05       0.03    1.51     0.13
## as.factor(Treatment)5     0.05       0.03    1.42     0.16

pSEM - Food Web Construction

m1<- glmmTMB(Chl.a.concentration~Treatment+ Temp + pH +
               (1|Tank)+ #random effects term to deal with spatial effects of tank
               ar1(Days+0|Tank), #temporal auto-correlative term
             data=expDat)
m2<- glmmTMB(Current.Density~Chl.a.concentration+denI+Treatment+
               (1|Tank)+ar1(Days+0|Tank),
             data=expDat, family = "poisson")
m3<- glmmTMB(TFTotalMass~Chl.a.concentration+denI+Treatment+Temp+
               (1|Tank)+ar1(Days+0|Tank),
             data = expDat)
x<- psem(m1, m2, m3, data=expDat)

pSEM

Time-to-Event

m4<- coxph(formula = Surv(days.x, status) ~ Treatment, data = anura)
m4Sum<- summary(m4)
round(m4Sum$coefficients, digits=2)
##           coef exp(coef) se(coef)    z Pr(>|z|)
## Treatment 0.15      1.17     0.06 2.44     0.01

Time-To-Event

Discussion

  • Systems could be resilient to salinization if strong food base is present
    • Could be at the detriment to less tolerant species
  • More food present, even at infavorable conditions can mean greater transport on to terristrial systems
    • Although favorable systems might still yield quicker transport, especially if system continues to worsen

Questions?

Repository

pSEM parts

## $cond
##                 Estimate Std. Error    z value  Pr(>|z|)
## (Intercept)  0.497083615 1.39681251  0.3558700 0.7219380
## Treatment    0.126180762 0.10768251  1.1717851 0.2412833
## Temp        -0.002022903 0.03488222 -0.0579924 0.9537547
## pH          -0.127196544 0.14409454 -0.8827298 0.3773823
## 
## $zi
## NULL
## 
## $disp
## NULL

pSEM parts

## $cond
##                        Estimate   Std. Error   z value     Pr(>|z|)
## (Intercept)          1.61165568 0.1881181580  8.567252 1.059837e-17
## Chl.a.concentration -0.05302042 0.0266678440 -1.988178 4.679202e-02
## denI                 0.01209269 0.0006217227 19.450301 2.897260e-84
## Treatment            0.07936172 0.0547277475  1.450118 1.470255e-01
## 
## $zi
## NULL
## 
## $disp
## NULL

pSEM parts

## $cond
##                         Estimate   Std. Error   z value     Pr(>|z|)
## (Intercept)          1.498417900 0.2400909299  6.241043 4.346618e-10
## Chl.a.concentration  0.051550009 0.0201664947  2.556221 1.058160e-02
## denI                 0.002453462 0.0005611301  4.372359 1.229111e-05
## Treatment            0.125999140 0.0293439883  4.293866 1.755888e-05
## Temp                -0.016890506 0.0086803654 -1.945829 5.167530e-02
## 
## $zi
## NULL
## 
## $disp
## NULL

Odonate TTE

##           coef exp(coef) se(coef)   z Pr(>|z|)
## Treatment 0.28      1.32     0.17 1.6     0.11