Agricultural expansion is the leading cause of biodiversity loss, with global cropland estimated at 1,244 Mha in 2019 (Potapov et al., 2022) and predicted to expand further by 193–317 Mha by 2050, mainly in Africa (Schmitz et al., 2014). This expansion will reduce available habitat for 87.7% of the 19,859 terrestrial vertebrate species recently reviewed by Williams et al. (2021), with 1,280 species losing >25% of their remaining range. Balancing the demands for crops and conservation is one of the biggest challenges of the 21^st century (Dudley and Alexander, 2017), especially in the tropics, where species diversity is high, and large natural ecosystems are declining due to human impacts (Cincotta et al., 2000; Pendrill et al., 2022). The impact of agriculture on non-human great apes (further referred to as “great apes”) in the Asian and African tropics is of particular concern, with chimpanzees, bonobos, Western and Eastern gorillas, and three species of orangutans all in decline and threatened with extinction within the coming decades ( Figure 1 , for scientific names see Table 1 ). The distribution and density of these species are primarily determined by habitat availability, disease, killing for meat and other purposes, and people’s attitudes to sharing landscapes with great apes. Despite national legislation legally protecting these species in all 23 countries they occur in, the threat to their survival remains high (Caldecott and Miles, 2006; Bettinger et al., 2021).

The remaining great apes (750,000-1,250,000, see Figure 1 ) share their distribution ranges with around 97 million people (1 great ape per 77-129 people, see Supplementary Materials and Table 1 ). In simple terms, one great ape shares resources with 100 humans, mainly in countries with high human population growth and poverty (i.e., income of less than US$2 per day), and low food security. For instance, according to World Bank data, the Democratic Republic of the Congo (DRC) has a 2.9% annual population growth rate, which could double the number of people living alongside great apes in 25 years. Some of the great ape range countries are also those with the highest levels of undernourishment: 21% of the Sub-Saharan people were undernourished in 2020 (The World Bank, 2022a). Thus, there is an urgent need for increased local food production and more equal distribution of food to improve food availability, affordability, and security. Growing human populations and a drive for economic development, alongside growing international demand, remain key drivers of deforestation (Busch and Ferretti-Gallon, 2017) and therefore great ape habitat loss.

The threats to great apes related to agriculture include habitat loss and fragmentation due to agricultural expansion, the resulting genetic factors related to small and isolated populations, agriculture-related diseases, as well as the human-great ape conflict, and ape killing, capture, and trade ( Figure 2 ). In terms of agricultural expansion, we focus on crops rather than livestock, because in the orangutan ranges livestock-related forest loss is rare, while, in Africa, such losses are concentrated in the drier parts where great apes generally do not occur (although chimpanzee habitat in Tanzania, Senegal, and Mali is a local exception). Maize (Zea mays L.), rice (Oryza spp.), millet (various species), and cassava (Manihot esculenta Crantz) are the main crops of concern (for details see Tables S1–S3 ). These are mostly grown in smallholder, subsistence agriculture contexts ( Table 1 ), with fields typically <0.64 ha in size (Lesiv et al., 2019), and further field size reduction ongoing (Abraham and Pingali, 2020). Rice, maize, and cassava show the most rapid expansion, while other crops such as sesame (Sesamum indicum L.), sunflower (Helianthus annuus L.), cotton (Gossypium L.) and okra (Abelmoschus esculentus (L.) Moench) have expanded but use up less land (FAOSTAT, 2023). African oil palm (Elaeis guineensis Jacq.) is another crop that has been a driver of deforestation, especially in Southeast Asia’s orangutan ranges ( Table S4 ), with concerns about its expansion in Africa and potential impact on great apes (Linder, 2013; Wich et al., 2014). While the media has extensively covered the effects of industrial oil palm expansion on great apes, there has been relatively little scrutiny on the impacts of other crops (Jayathilake et al., 2021).

There is considerable variation in the type of crops grown across the great ape range ( Supplementary Materials ). Most African great apes reside in tropical evergreen forests, but some populations are also found in deciduous woodland and drier savannah-dominated habitats interspersed with gallery forests. The crops grown in these areas are adapted to equatorial fully humid, monsoonal, summer dry, and winter dry conditions (Kottek et al., 2006). The regions primarily cultivate annual crops, although there are also perennial crops such as oil palm, tree crops, and cacao ( Table 2 ). The use of crop areas by great apes for feeding or dispersal, and the level of persecution they face for consuming different crops, vary depending on the type of crop cultivated and species ecology ( Supplementary Materials ). Soil fertility may also influence great ape presence, with areas in Borneo that have low soil fertility and are poorly suited to agriculture, traditionally being used by nomadic hunter-gatherer people who likely hunted out orangutans in the past (Meijaard, 2017). It remains unclear whether this also applies to Africa, although the more fertile parts, such as volcanic mountain slopes (see, e.g., Hengl et al., 2021) seem to retain species such as mountain gorillas.

Only some areas of the remaining great ape habitat are formally protected. For example, 83% of chimpanzees in West Africa (Heinicke et al., 2019) and about 80% of central chimpanzees and western gorillas in Central Africa reside outside protected areas (Kormos et al., 2003; Brncic et al., 2015; Tweh et al., 2015; Strindberg et al., 2018). Additionally, about 50% of orangutans in Indonesian Borneo reside outside protected areas (Meijaard et al., 2022b). These unprotected habitats are under particular threat from agricultural expansion, though even protected areas can be vulnerable – depending on management, and the extent to which community needs are integrated into protected area management. Overall, understanding the distribution and ecology of great apes is crucial in understanding the threat posed by agriculture.

The different characteristics of the fourteen great ape species and subspecies ( Table 1 , Supplementary Materials ), the different regions of the world in which they occur, and the different agricultural crops that may threaten their habitats or provide some ecological opportunities to them ( Table 2 ), result in a complex picture regarding the relationship between agriculture and great apes. This is further confounded by the scales at which crops are produced (e.g., smallholder or industrial scale), growth types (annual or perennial, monoculture or inter-cropped) or whether crops are produced for subsistence or cash-income purposes. Here we review the literature on great apes and agriculture. Because of the complex nature of the topic and the often qualitative evidence presented in published sources, we use literature review with narrative synthesis to generate insights about the apes and agriculture interface (Grant and Booth, 2009). We searched the scientific literature for papers on great apes in agricultural contexts using species names as search terms, combined with agriculture-related search terms, but did not conduct a formal quality assessment. Trends in land use associated with various crops were determined using data provided by the United Nations Food and Agriculture Organization. Our objectives are to 1) assess the dominant crops and food systems in the ranges of the 14 great ape species and subspecies; 2) identify antagonistic and synergistic co-occurrences; 3) understand economic and political factors that might influence future agricultural developments; and 4) provide recommendations towards improved co-existence between apes and agriculture. We hope to clarify how future agricultural developments are likely to affect different great ape taxa, and what can be done to minimize negative impacts.

In Africa, agricultural production mainly serves domestic consumption with few crops generating export revenues (Rakotoarisoa et al., 2012). Smallholder farming dominates, although a transition to business-oriented processes is underway (Mukasa et al., 2017; Giller, 2020). Farms still struggle to provide food security or living incomes. Production is expected to increase (Sanchez, 2002; Pendrill et al., 2022; Potapov et al., 2022), putting further pressure on land, especially in Ghana, Ivory Coast, Benin, Nigeria, and Cameroon (Halpern et al., 2022). Infrastructural development related to extractive industries (Weng et al., 2013) is linked to agricultural growth corridors (Independent Science and Partnership Council, 2016), impacting areas of high biodiversity (Laurance et al., 2015).

Agricultural expansion on Borneo and Sumatra has led to major forest loss since the 1970s (Wilcove et al., 2013). These tropical islands are highly suitable for the cultivation of crops such as oil palm, with rice, rubber (Hevea brasiliensis Müll. Arg.), maize, coconut (Cocos nucifera L.), and coffee (Coffea arabica L.) also grown ( Table S4 ). Oil palm agriculture is dominated by large-holders, but while there is more industrial-scale agriculture compared to African great ape ranges ( Table 1 ), forest loss has declined recently due to improved governance of this sector (Gaveau et al., 2019; Gaveau et al., 2022). Nevertheless, soil impoverishment and economic factors drive smallholder farmers to clear forests (Duffy et al., 2021), especially low nutrient peat swamp forests that are important for orangutans (Meijaard et al., 2010).

Across Sub-Saharan Africa and South-East Asia, agricultural expansion is leading to significant changes in land use patterns, with certain crops showing particularly rapid rates of growth. Cassava, oil palm, and rubber have been the crops with the greatest regional expansion rates ( Table 2 ). Meanwhile, land under maize is also expanding, and if current regional trends continue, it may approach equivalence with the area under rice within the next decade. Two other crops, yams (Dioscorea spp.) and plantain (Musa spp.) have also seen significant increases in area between 2010 and 2021, with respective growth rates of 87.0% and 55.2% (FAOSTAT, 2023).

There is considerable variation in crop distribution across different regions. In Central Africa, for instance, which is home to bonobos, chimpanzees, and Western gorillas, the largest areas are allocated to cassava, maize, groundnuts (Arachis hypogaea L.), sorghum (Sorghum bicolor L. Moench), and rice ( Table S1 ). Meanwhile, in West Africa, which is home to chimpanzees and Cross-River gorillas, sorghum, maize, and cow peas dominate ( Table S2 ). While the effects of climate change on crop distribution are unclear, it is likely that areas with rain-fed agriculture and limited economic and institutional capacity to respond to climate variability and change, such as some parts of West Africa, will be negatively impacted through yield losses (Sultan and Gaetani, 2016). Such losses could increase pressure on the remaining forested areas where great apes live. In Borneo, predicted reductions in rainfall and increases in temperature (McAlpine et al., 2018) are likely to limit areas suitable for crops such as oil palm, which is vulnerable to prolonged drought, and reduce available orangutan habitat (Struebig et al., 2015).

Great apes react differently to reduction in forest habitats and changing foraging opportunities and threats (see Supplementary Materials for short species ecology reviews). The species are primarily adapted to a plant diet – with meat consumption by chimpanzees being an exception (Fahy et al., 2013) – and may target crops in fields or fruit and trees in orchards and plantations, especially when wild foods are scarce, but also because these may be preferred, since they are highly nutritious and easy to access (Hockings and Humle, 2009; Hockings et al., 2009; Campbell-Smith et al., 2011; Hockings and McLennan, 2012; Seiler and Robbins, 2016). Great apes and humans also share the need for water (Box 1).

Preliminary studies indicate that individuals in some great ape species change their behavior over time to human-dominated landscapes (Hockings et al., 2015), changing food items as they learn what is edible and learning to navigate agricultural lands (McLennan and Hockings, 2014; Ancrenaz et al., 2015; McLennan et al., 2021). These behaviors are often maladaptive, as the nutritional benefits can be outweighed by the costs of increased mortality through accidental snaring, retaliatory killings, and disease. As species with low reproductive outputs, retaliatory killings of apes by humans in response to crop consumption are unlikely to be sustainable. Disagreements between different human groups over how to manage problematic great ape behavior can follow (Campbell-Smith et al., 2011; Hockings and McLennan, 2012).

Great apes can coexist with humans in shared landscapes, but local attitudes towards them determine whether this is beneficial or harmful. Coexistence requires humans and wildlife to co-occur (Harihar et al., 2013), with tolerable risks to both, and should be sustainable (Carter and Linnell, 2016). Some sites have shown co-adaptation between chimpanzees and smallholder agriculture (Halloran, 2016; Bersacola et al., 2021; McLennan et al., 2021), while orangutans survive in forest fragments in Malaysian oil palm landscapes because people accept their presence (Ancrenaz et al., 2021). People in the latter landscape are generally not concerned about orangutans or crop losses, and orangutans are generally safe, although it is unclear if these fragmented populations will remain viable in the long-term (Oram et al., 2022). Conservation planning for great apes needs to consider whether agricultural expansion is driven by poverty and if killing of great apes may continue, or if more stable conditions can be achieved.

Preventing agricultural expansion is the best way to minimize negative impacts on great apes, but this can be difficult in regions with undernourishment and poverty (Meijaard et al., 2022a). Areas of poverty often coincide with relatively good forest protection (Busch and Ferretti-Gallon, 2017), but transitioning to middle-income levels may accelerate agricultural development and pose a threat. Reducing poverty without deforestation requires greater stakeholder engagement (Garcia et al., 2020), such as involving communities in forest enterprise (Santika et al., 2019), although the broader applicability of such models across great ape ranges remains unclear. Also, even when deforestation rates can be reduced, reducing poaching rates is challenging and requires long-term financing (Sandker et al., 2009).

Efforts to reduce forest loss and poaching rates whilst alleviating poverty could help reduce pressures on great ape populations and habitats as economies develop, i.e., the forest transition (Mather and Needle, 1998). In Africa, deforestation is thought to be positively related to real Gross Domestic Product (GDP) per capita until a turning point around USD 3,000 per capita income, beyond which deforestation is expected to decline (Ajanaku and Collins, 2021). African apes are most threatened in areas with low to medium poverty, growing GDP, expanding agriculture, and growing rural populations (Tranquilli et al., 2012). Local economic development that spares forest or development away from forest areas could reduce population pressure and forest losses. The Sub-Saharan region is already undergoing rapid urbanization with forecasts indicating that ca. 58% of its population is going to live in cities by 2050 compared to ca. 40% now (UNDESA, 2019). Nevertheless, although overall annual growth rates have declined from 2.4% in 1980 to 1.7% in 2021 (The World Bank, 2022b), rural population growth is likely to continue. Resulting migration patterns in Sub-Saharan Africa are complex, even more so when driven by armed conflict (Mercandalli et al., 2019). While poverty levels may locally prevent deforestation, these may not be a good predictor of great ape survival itself. Ordaz-Németh et al. (2021) found a negative quadratic relationship between African great ape densities and GDP, with decreasing great ape densities, partially poaching-related, above a nationwide GDP of $5 billion annually, which translates into a per capita GDP for these countries between USD 500 and 2,500. The effects of GDP maybe therefore play out differently on deforestation and poaching, and poverty and income levels as such may be poor predictors of great ape survival.

The debate on land sharing versus land sparing is relevant to reducing negative interactions between people and great apes (Phalan et al., 2011; Law and Wilson, 2015). Land sparing aims to set aside large tracts of land for exclusive wildlife use while intensifying agriculture on existing farmland to keep people and great apes apart. Land sharing seeks coexistence between people and great apes through small-scale farming and sustainable forest management in patchworks of low-intensity agriculture. Empirical evaluations suggest that land sparing results in better outcomes for wildlife diversity and abundance in the short term (Phalan et al., 2011; Hulme et al., 2013; Williams et al., 2017), but others note that isolated protected areas within an agricultural matrix can increase inbreeding and vulnerability to extinction (Kremen and Merenlender, 2018). This has been demonstrated in orangutans (Bruford et al., 2010) and Cross-River gorillas (Bergl et al., 2008), although such effects will depend on the extent to which apes use the matrix. The impacts of intensive agriculture, such as the use of fertilizers, herbicides, fungicides, and pesticides (Matson and Vitousek, 2006; Dudley and Alexander, 2017), can also be harmful to great apes (Krief et al., 2017). Research suggests that intensification does not necessarily reduce the area under agriculture because high yields drive further agricultural expansion (Byerlee et al., 2014; Balmford, 2021). The reality for great apes is likely to remain a mixed sharing and sparing model, where parts of their remaining range will need to be included in protected areas while others will need to be shared with farmers (Meijaard et al., 2022b). Protected land is still necessary in these shared landscapes due to the low reproductive rates of great apes, their area requirements, and crop foraging. Therefore, land sparing-type solutions that safely protect habitat fragments and keep them connected are required for the synergistic coexistence of people and great apes (Ancrenaz et al., 2021).

The coexistence of great apes and agriculture is challenging and a win-win situation for both is difficult to achieve. Agricultural expansion, often associated with people without prior experience of great ape coexistence moving into great ape areas, is likely to cause further declines in ape populations. This makes sustainable and resilient interactions between people and nature difficult to achieve. If we truly want to save great apes from extinction, then we must prioritize implementing strict spatial planning and rigorous enforcement measures, that are ideally co-developed with local communities. This includes designating no-farming areas, improving crop productivity and diversification, resolving human-wildlife conflicts, securing adequate conservation financing, and clearly defining the roles and responsibilities of different stakeholders ( Table 3 ). Without a committed and sustained effort in these areas, the survival of great apes will remain uncertain, and the consequences of their extinction will be irreversible. Finding solutions that work for great apes would have implications for many other threatened species in similar socio-ecological contexts across the tropics.

Great apes face competition for land and resources with humans, particularly where crops such as rice, cassava, maize, cacao, and oil palm are grown within their ranges ( Table 3 ). This creates trade-offs between reducing poverty, feeding people, and conserving the environment. To address this, strategies must tackle the root causes of the problem, including land use competition. We suggest a framework for discussion, presented in Figure 5 , focused on three directions. The first is to increase food production sustainably through agricultural innovations and smarter land use practices. The second is to modify food consumption patterns and distribution systems to reduce pressure on land and resources. Alternative food sources with minimal impact on great apes, including imported foods, might be effective under specific conditions. Though such lifestyle changes could raise complex issues related to food security and trade considerations. The third direction focuses on generating alternative income.

We emphasize the importance of adopting a landscape and jurisdictional approach in managing the competition between humans and great apes (Sayer et al., 2013). Within this framework, we propose several solutions, including strategies to increase yield, produce-and-protect practices, and threat management techniques. Next, we explore potential strategies to improve alternative income sources for communities, thereby reducing the need for land exploitation that can trigger competition with great apes ( Figure 4 ). Finally, we consider the need to rethink our food systems in the context of the competition with great apes. We analyze potential solutions on both the consumption side and the production side, including modifying local food systems (e.g., by promoting dietary changes among local communities, such as switching from rice or maize to other crops) and global food systems (e.g., by reducing waste and rethinking food versus materials use) ( Figure 5 ).

Great apes face significant threats from agriculture driven by poverty and demand for agricultural resources. Ensuring coexistence between great apes and people is of paramount importance, particularly considering that most great apes live outside protected areas. However, the challenge lies in the fact that on average each great ape shares its distribution range with approximately 100 people. Achieving successful coexistence requires significant incentives and efforts to protect and preserve these conservation flagships. New financial models are needed that can more easily be scaled up and attract =more investment. Optimized land use planning, guided by strategic investments in agricultural development and wildlife conservation, can maximize synergies between conservation and food production goals. It is vital to support effective economic development policies, enforce forest conservation and environmental laws, engage in trade policy discussions, and link policies on trade, food security, improved agricultural techniques, and sustainable food systems with forest and great ape impact monitoring. The global agenda should focus on closing crop yield gaps, promoting healthier diets, reducing food loss and waste, and allocating more research funding to address the challenges of great ape and human coexistence.

EM, RD, MA, SWi and DS contributed to conception and design of the study. NU, TA and RD organized the database and spatial analysis of crop and other data. JS developed the causal change diagrams. EM wrote the first draft of the manuscript. KH, SWu, CG, MO, JL, JR, and DS wrote sections of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.