Figures and data in Risk-taking incentives predict aggression heuristics in female gorillas

Figures
Tables
Additional files

3 figures, 3 tables and 1 additional file

Figures

Figure 1

Download asset Open asset

Calculation of the interaction score.

The lower the rank of the aggressor and the greater the rank of the recipient, the greater the score (-1 to 1; line thickness). Arrows start from aggressors and point to recipients of aggression. We created the figure using a female gorilla silhouette icon from http://phylopic.org (created by T. Michael Keesey) and TikZ (TeX).

Figure 2

Download asset Open asset

Distribution of interaction score (recipient-aggressor rank difference).

Density of the mild, moderate, and severe aggression as a function of the interaction score. Positive scores represent aggression up and negative scores represent aggression down the hierarchy.

Figure 3

Download asset Open asset

Predicted interaction score (recipient-aggressor rank difference) of aggressive interactions (n=6871) as a function of the explanatory variables of the linear mixed effects model with a significant effect: number of adult males in the group, number of adult females in the group and aggressor’s reproductive state (Cycl: cycling; P_n: nth pregnancy trimester; Lact: lactating).

Shaded areas and whiskers show 95% confidence intervals. We created the figure using R package *effects* (Fox et al., 2022). Positive scores represented aggression up and negative scores represented aggression down the hierarchy.

Tables

Table 1

Study groups, study period, average number of females per day (± s.d.; total number of females in the group in parentheses), and number of aggressive interactions (mild - moderate - severe).

Group name	Study period	Number of females	Aggression (mild-moderate-severe)
ATA/Atananga	2017–2023	3.30±0.85 (6)	208 - 65 - 27
BIT/Bitukura	2015–2023	4.14±0.35 (6)	509 - 35 - 23
KYA/Kyagurilo	1999–2016	6.07±1.02 (9)	3256 - 445 - 315
MUK/Mukiza	2016–2023	6.59±1.20 (8)	1389 - 89 - 141
ORU/Oruzogo	2014–2023	5.59±0.96 (8)	55 - 7 - 7

Table 2

Results from the linear mixed-effects model.

Significant p-values appear in bold. The significance of each level of a categorical variable was evaluated against the reference level (placed in parenthesis) according to whether their 95% confidence intervals (CI) include zero or not. ‘Pregnant_n’ denotes the nth trimester of pregnancy. To highlight that aggression rates can increase due to an increase in interactions of different score, we include a last column with the effect of some of the tested variables on overall adult female aggression rates, based on results of linear mixed effects models from Smit and Robbins, 2024. ‘ns’: non-significant correlation; ‘+’: positive correlation; ‘-’: negative correlation; ‘na’: not tested (see Smit and Robbins, 2024 for details).

Response variable: Interaction score (recipient-aggressor rank difference)						Aggression Rate (from Smit and Robbins, 2024)
Fixed factor	Level	Estimate	95% CI	Chisq	p-Value	Aggression Rate (from Smit and Robbins, 2024)
Species (mountain)	Western	0.088	[–0.495; 0.671]	0.088	0.767	ns
Reproductive state (Cycling)	Pregnant_1	0.130	[0.101; 0.159]	138.812	<0.001	+*
	Pregnant_2	0.093	[0.063; 0.123]	138.812	<0.001	+*
	Pregnant_3	0.146	[0.114; 0.177]	138.812	<0.001	+*
	Lactating	0.043	[0.027; 0.059]	138.812	<0.001	-
Number of females		–0.011	[–0.018; –0.003]	8.045	0.005	+
Number of males		0.018	[0.010; 0.026]	19.784	<0.001	-
Aggression intensity (Mild)	Moderate	–0.030	[–0.051; –0.009]	8.531	0.005	na
Aggression intensity (Mild)	Severe	–0.014	[–0.036; 0.009]	8.531	0.229	na

*

Pregnancy was not divided in trimesters in Smit and Robbins, 2024.

Table 3

Results of post hoc pairwise comparisons among reproductive states, from the linear mixed effects model.

Significant p-values appear in bold. Cycl: cycling; P_n: nth pregnancy trimester; Lact: lactating.

Comparison	Estimate	Std. error	Z-value	p-Value
P1-Cycl	0.130	0.015	8.681	0.000
P_2 - Cycl	0.093	0.015	6.071	0.000
P_3 - Cycl	0.146	0.016	9.147	0.000
Lact - Cycl	0.043	0.008	5.236	0.000
P_1 - P_2	–0.037	0.019	–1.965	0.267
P_1 - P_3	0.016	0.019	0.812	0.922
Lact - P_1	–0.087	0.015	–5.888	0.000
P_2 - P_3	0.052	0.019	2.721	0.047
Lact - P_2	–0.050	0.015	–3.368	0.006
Lact - P_3	–0.103	0.015	–6.715	0.000