Ongoing ecosystem change and biodiversity decline across the Afrotropics call for tools to monitor the state of African biodiversity or ecosystem elements (e.g., completeness and integrity) across extensive spatial and temporal scales. We assessed relationships in the co-occurrence patterns between great apes and other mammals, to evaluate if ape abundance serves as proxies of mammal diversity across broad spatial scales. We used camera trap footage recorded at 22 sites, each known to harbor a population of chimpanzees and/or gorillas, across 12 sub-Saharan African countries. From ~350,000 1-minute camera trap videos recorded between 2010 and 2016, we estimated mammalian community metrics [i.e., (species) richness, (Shannon) diversity, and body mass (hereafter simplified as “animal mass”)]—considering only medium and large-bodied species — and fitted Bayesian Regression Models to assess potential relationships between ape abundances and these metrics. We included site-level protection status, human footprint, and precipitation variance as control variables. We found that relationships between the abundance of great apes and the total abundance and body mass of non-ape mammals were largely positive. In contrast, relationships between ape abundance and mammal richness were less clear, except chimpanzee abundance as a predictor of mammalian richness inside protected areas and areas with high human impact. Relationships between ape abundance and mammal diversity were largely negative for both species, in that sites with higher ape abundances had mammalian communities with relatively uneven abundance distributions. Our findings suggest that gorillas and chimpanzees hold potential as indicators of specific elements of mammalian communities, especially population-level (abundance) and composition-related (body mass) characteristics. Monitoring ape populations may inform ecosystem management: declines in ape populations may serve as early warning signals and indicate a need for conservation interventions, as changes in ape abundance and community composition are likely to precede extirpation of other mammal species.