African monkey responses to climate change in 3 publications
Climate change may not be the greatest threat to primates, but it will affect them both directly and indirectly because it can restrict the ability of primates to cope with other anthropogenic changes (especially hunting and deforestation). Over a set of four papers, colleagues and I investigated time budget constraints (driven by climatic conditions and biological traits) and biogeographical distributions of two African monkey genera: arboreal guenons (Cercopithecus/ Allochrocebus) and black-and-white colobus (Colobus). In the final publication in a new UNESCO report I bring together the results of these studies to investigate how climate change is likely to affect these two monkey genera.
From 2003-2006 I had the honour of working with Robin Dunbar At Liverpool University to develop time budget models on primates, together with Julia Lehmann. The first paper we published compared time constraints of two African leaf-eating monkeys: colobine genera (Colobus and Procolobus/ Piliocolobus) see here. We used the relationships between climate, group size, and time budget components for populations of Colobus and Piliocolobus at different research sites, to create 2 taxon-specific time-budget models. In both genera, feeding time increased with group size or biomass, showing an effect of food on competition. Time constraints correctly predicted presence or absence of the genera at >84% of >150 African primate sites. Time constraints, as a result of slight dietary differences, also correctly predicted that group sizes for the genus Colobus are less than half those for the genus Piliocolobus. The models, based on time constraints, could therefore explain the differences between the genera in distrbutions and group sizes: Piliocolobus is less wide-spread across Africa but typically lives in larger groups than Colobus. We show that the differences between the 2 genera are due mainly to intrinsic differences in the way each taxon’s digestive physiology interacts with climatic variables to influence resting time requirements.
Since that time I was also trying to complete a similar analyses on time budget for arboreal guenons, Cercopithecus/ Allochrocebus. These African fruit-eating monkeys are very diverse and far more very widespread across sub-Saharan Africa than the colobines. They typically live in relatively small groups, similar to the genus Colobus. After all these years it has now come out as a publication in the International Journal of Primatology in August 2018. The study showed that time constraints, through competition, could not really explain the small group sizes in this genus (although feeding time was again influenced by group size, the effect was really small). Time constraints models could, however, effectively show distribution patterns of the species across Africa. Especially, constraints in resting and moving time investments drive the distribution of these species: when the climatic conditions lead to high resting time requirements (e.g. high temperatures and great temperature seasonality), the species cannot survive. Body mass and leaf consumption were important drivers of the models.
As a result of those projects, I became more an dmore interested in understanding primate distribution patterns and how climate change would influence these patterns. In 2016, Alyson Hillyer and I wrote a review chapter on the effects of climate change on primates. That chapter appeared in the 2016 book An Introduction to Primate Conservation, edited by Serge Wich and Andrew Marshall. Thanks to that paper, I was invited to an international workshop organised by the HEADS (Human Evolution: Adaptations, Dispersals and Social Developments) programme at UNESCO Mexico.
We had a great meeting in Mexico City in September 2017 with primatologists working in Africa, the Americas and Asia. We discussed our concerns with regards to the future of primates and the role that primatology can play in supporting conservation efforts.
The UNESCO book that followed from the meeting discusses our concerns about climate change, and the threats to non-human primates from environmental disruption, degradation and fragmentation in the tropics, along with bush meat, poaching and pet trafficking. We also spoke about the relationships between non-human primates and humans and the role that local communities in non-human primate habitat countries play in conservation.
At the time I was also completing a chapter for a book edited by Alison Behie, Julie Teichroeb, and Nick Malone: Primate Research and Conservation in the Anthropocene. For that chapter, I compared distribution patterns and the potential effects of climate change on the distributions of two African monkey genera that I knew well from my own previous research: Colobus and Cercopithecus. Comparing these genera is interesting because they both occupy similar forest and woodland environments, but the genus Colobus has special adaptations (e.g. multi-chambered stomachs) to more effectively digest leaves, whilst the genus Cercopithecus consumes ripe fruits and insects, supplemented with leaves. I show that future range reduction is severe for Colobus but minimal for Cercopithecus. Suitable habitats for Colobus are predicted to become restricted to central African regions. The analyses show that species that appear to have similar habitat requirements may still respond very differently to predicted climatic changes.
So for the section in the UNESCO report, Emma Hankinson, Helen Slater and myself bring those previous publications together to investigate the impact of climate change on the genera Cercipithecus and Colobus according to models based on distribution patterns and those based on time constraints. The summary of this analysis can be seen in the Table 1 below. Overall, the analyses showed that the two approaches to investigating drivers behind primate distributions produced slightly different outcomes but both agreed that overall, the predicted higher future temperatures will negatively affect especially leaf eaters because it reduces leaf quality, but affects all primates by forcing them to rest more. Rainfall patterns in Africa are changing in less consistent ways, some areas (e.g. East Africa) will see increased rainfall whilst others (e.g. West Africa) will see decreased rainfall. These differences are already clearly being picked up in long-term primate field sites. Generally, more rain is better, as long as it is not too much. Greater temperature variation at the 24 hours scale is generally not good for primates but the predictions for the future do not show a huge consistent change in this variable. Temperature variation across calendar months generally is expected to increase across Africa and this will negatively influence the monkeys because, as tropical species, they are not well adapted to great seasonality. Rainfall variation across calendar months is expected to increase in the future for most areas in sub-Saharan Africa and generally greater variation is not good for primates because long dry seasons reduce food productivity. This is also reflected in a predicted average decrease in the length of the growing season, i.e. the number of months per year in which rainfall in mm is twice the average temperature in that month (P>2T), a variable introduced by Le Houerou and important in many of our time budget models. This decrease in months in which the environment is more productive (plants get enough water to deal with evaporation) negatively affects most primates.
MXLLS
Overall, the picture looks better for the fruit-eating arboreal guenons than for the leaf-eating arboreal colobines.
References:
Korstjens, A.H. (2019): Chapter 14 The Effect of Climate Change on the Distribution of the Genera Colobus and Cercopithecus. In: Behie, A., Teichroeb, J., & Malone, N. (Eds.). Primate Research and Conservation in the Anthropocene. Cambridge Studies in Biological and Evolutionary Anthropology. Cambridge: Cambridge University Press: pp 255-278 (PDF upon request). doi:10.1017/9781316662021
Korstjens, A.H., Slater, H.D., Hankinson, E, (2018). Predicting African primate species’ responses to climate change. In: Primatology, Biocultural Diversity and Sustainable Development in Tropical Forests. UNESCO HEADS (Human Evolution: Adaptations, Dispersals and Social Developments Programme) report. pp186-205.
Korstjens, A.H., Lehmann, J. & Dunbar, R.I.M. (2018) Time Constraints Do Not Limit Group Size in Arboreal Guenons but Do Explain Community Size and Distribution Patterns. Int J Primatol. 39: 511. https://doi.org/10.1007/s10764-018-0048-4 Open access.
Korstjens, A. H. & Hillyer, A., (2016). The effect of climate change on primates: a review of current knowledge. In: Wich, S.A. & Marshall, A. J. (eds). An Introduction to Primate Conservation. Oxford Univ Press.
Korstjens, A. H., & Dunbar, R. I. M., 2007. Time constraints limit group sizes and distribution in red and black-and-white colobus monkeys. Int J Primatol, 28(3):551-575
