From female choice to social structure: Modeling harem formation in camelids

TL;DR

This work has developed an individual-based stochastic model in which camelid females transition between different familial groups in response to their environmental conditions, aiming to maximize individual fitness.

Abstract

Herbivorous wild species constantly strive to optimize the trade-off between energy and nutrient intake and predation risk during foraging. This has led to the selection of several evolutionary traits -- such as diet, habitat selection, and behavior -- which are simultaneously shaped by the spatio-temporal variability of the habitat. Among camelid species, polygyny is a prevalent behavioral strategy that encompasses both mating and foraging activities. This group-level behavior has multiple interacting dimensions, contributing to an interesting ecological and evolutionary complexity. We developed an individual-based stochastic model in which camelid females transition between different familial groups in response to their environmental conditions, aiming to maximize individual fitness. Our results indicate that the behavioral strategy of individual females can shape, by itself, emergent population-level properties, including group size and fitness distribution. Furthermore, these properties are modulated, in a non-additive manner, by other factors such as population density, sex ratio and system heterogeneity.

Figures (12)

• Figure 1: Schematic representation of the payoff calculation network used to define each female's probability distribution to switch group. In this example, the total number of females is $F_T$ = 12, with three existing harems and $B$ bachelors. Each female evaluates the potential payoff for each group based on her current position and the possible changes in the bachelors population.
• Figure 2: Proportion of males with a group (harem) over time (MCS) for different combinations of $M_t$ and $F_t$, as indicated in the figure. In all cases, the parameters are fixed as follows: $R = 20$, $H = 5$, $c = 1$, $\beta = 1$ and $\sigma = 1$. The respective averages are shown in a contrasting color.
• Figure 3: Empirical cumulative density functions at different times $t$, calculated from the states vectors $S_t$. The inset shows the Kolmogorov–Smirnov distance between consecutive state vectors over time, compared to the theoretical threshold $D_c$.
• Figure 4: (A) Heat map of the fraction of males with an harem, for different combinations of number of males ($M_t$) and females ($F_t$) in the system. (B) Heat map of the Global Gini index of the females distribution, also for different combinations of $M_t$ and $F_t$. Each pixel is the average of 20 realizations. Besides, $R = 20$, $H = 5$, $c = 1$, $\beta = 1$, $\sigma = 1$.
• Figure 5: Heat maps of the Group Gini index (excluding bachelor males) for different combinations of total number of males ($M_t$) and females ($F_t$) in the system, for two different levels of resources, $R$. A) $R = 20$; B) $R = 500$. Each pixel is the average of 20 realizations. Other parameters are: $H = 5$, $c = 1$, $\beta = 1$, $\sigma= 1$. Note that the color-scale is limited from 0.0 to 0. 35 for visualization purposes.