**3.1 Seasonal variations and environmental parameters driving the densities of the snail's hosts**

We collected a total *895 Biomphalaria pfeifferi*, including 83 in Dry1 (9.27%), 192 in Dry2 (21.45%), and 620 in rainy (69.28%) seasons (**Table 1**). A factor for season in our forest plot analyses was a significant predictor of snail abundance (**Table 2**, *p-value* = 0.003), with both greater mean of total density (*N*) and maximum snail density per visit occurring in the rainy season (**Table 1**). In contrast, all measures of snail abundance were lowest during Dry1 season, whereas a medium density occurred in Dry2 season (**Figure 3**). Our forest plot analyses suggested that snail abundance in the rainy season was significantly different from season Dry1, whereas season Dry2 had lower but not significantly lower snail abundance compared to the rainy season (**Figure 2**; *p-value* = 0.181).

During Dry1 season, when snail abundance was lowest, no environmental parameters had a significant association to *Biomphalaria* abundance (**Table 1**;


#### **Table 1.**

*Total, mean and maximum of the total and seasonal densities of* Biomphalaria pfeifferi*.*


#### **Table 2.**

*Forest plot analyses of* Biomphalaria pfeifferi *abundance across seasons.*

*Seasonal Variations of Densities of* Biomphalaria pfeifferi*, the Intermediate Host… DOI: http://dx.doi.org/10.5772/intechopen.99217*

#### **Figure 3***.*

*Plot showing the distribution of* Biomphalaria pfeifferi *across the seasons. The greatest density was collected during the rainy season (with a peak >75) while the weakest was found during the Dry1 season.*


#### **Table 3.**

*Linear regressions between environmental factors and density of Biomphalaria pfeifferi for each season of snail sampling.*

**Figure 3**; *p-value* > 0.05)*.* In contrast, several environmental factors were significantly correlated to the snail host abundance in season Dry2 (**Table 3**). Conductivity and pH were negatively (*r* < 0) and significantly associated to hosts abundance whereas other drivers are positively (*r > 0)* correlated in season Dry2. The maximum water temperature (32.5° C) was obtained during rainy season. Water temperature was positively related to snail abundance, exerted a significant effect only in the season Dry2 (**Table 3** and **Figure 3**). There was no significant effect of temperature on snail densities in the rainy season (p-value = 0.549). Only the dissolved oxygen (p-value = 0.04) and periphyton (p-value = 0.003) were significantly correlated to the density of hosts in the rainy season. Periphyton was a significant positive predictor of snail abundances in both the Dry2 and rainy seasons (**Figure 4**).

**Figure 4.**

*Linear model assessing the significance of predictor-response relationships between environmental parameters and* Biomphalaria pfeifferi *densities across the seasons.*
