Can positive interactions between cultivated species help to sustain modern agriculture?

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Positive interactions between species (in which onespecies creates favorable conditions for another

species) or complementary resource use between speciesoccur frequently in terrestrial, wetland, and marine ecosys-tems (Callaway 1995; Bruno et al. 2003; Hughes 2012).Such interactions are recognized as playing important rolesin the structuring of biological communities (Tirado andPugnaire 2005; Baumeister and Callaway 2006) and in thefunctioning of ecosystems (Cardinale et al. 2002). In addi-tion to being successfully applied to restoring degradedenvironments (Padilla and Pugnaire 2006; Halpern et al.2007; Siles et al. 2008), positive interactions betweenspecies (eg plant–plant species interactions, plant–animalspecies interactions) have also been used to sustain localfood production in many traditional agricultural systems(Altieri 2004; Li et al. 2007; Xie et al. 2011). In contrast totraditional agriculture, modern agriculture generallyinvolves large-scale tracts of land, mechanization, andchemical fertilizers and pesticides. Monocultures are com-mon in modern agricultural systems and require substantial

input of fertilizers and pesticides, while the possible benefi-cial effects of species interactions are largely ignored(Omer et al. 2007). Although current agricultural tech-niques have greatly increased crop yields over the past halfcentury, heavy application of chemical fertilizers and pesti-cides has resulted in environmental pollution, pesticideresistance, and rising economic costs (Tilman et al. 2002,2011). These constitute major challenges to producing suf-ficient food for growing human populations while minimiz-ing the negative environmental effects of crop cultivation(Godfray et al. 2010). To help meet these challenges,researchers have suggested placing greater emphasis on theuse of biotechnology (Tester and Langridge 2010), preci-sion agriculture (an information-based management sys-tem for agricultural production, where exact amounts ofresources [nutrients and water] and pesticides are used;Gebbers and Adamchuk 2010), and organic farming(Reganold et al. 2011). In addition, a growing number ofstudies have explored the use of species diversity and posi-tive species interactions to improve agricultural yields (Liet al. 2007; Letourneau et al. 2011; Reganold et al. 2011;Kremen and Miles 2012; Chen and Tang 2013).

Here, we synthesize recent advances in our understand-ing of how within-field crop interactions can enhance sus-tainable food production while minimizing environmen-tal damage and then apply this information to develop aframework for future agriculture systems that integratesthe use of positive interactions between species with otherapproaches (eg biotechnology, mechanical and informa-tion-based technologies). First, we review recent studiesconcerning the effects of positive interactions betweenspecies in natural ecosystems and highlight their impor-tance in managed systems. Next, we investigate severalagricultural systems in which positive species interactionshave already been used to achieve local sustainability, andexplain how agricultural systems can benefit from such

REVIEWS REVIEWS REVIEWS

Can positive interactions between cultivatedspecies help to sustain modern agriculture? Weizheng Ren†, Liangliang Hu†, Jian Zhang, Cuiping Sun, Jianjun Tang, Yongge Yuan, and Xin Chen*

The importance of positive interactions between species within natural ecosystems and species associated withtraditional agriculture is well recognized. However, modern agriculture generally depends on monocultures,where positive interactions between cultivated species (ie in which the presence of one species facilitates the sur-vival, growth, or reproduction of other species) are largely ignored. Here, we review recent studies focused on thepositive interactions between cultivated species, consider how three traditional agricultural systems(legume–cereal intercropping, rice–fish co-culture, and agroforestry) have benefited from such interactions, andexamine how these benefits are affected by climate, planting patterns, and field management. Finally, wepropose a framework to illustrate how these interactions may improve modern agriculture through: the selectionof species–species partnerships; the development of specialized field machinery (in each case); field structure andconfiguration; field management; and farmer and societal acceptance.

Front Ecol Environ 2014; 12(9): 507–514, doi:10.1890/130162

In a nutshell:• Modern agriculture must be improved if it is to meet future

food and environmental requirements• The positive interactions observed between species in nature

and in traditional agriculture provide valuable opportunitiesto improve the sustainability and yields of modern agriculture

• Using such interactions to advance modern agriculture willrequire developing new technologies, selecting appropriatespecies–species partnerships, implementing farmer incen-tives, and gaining societal acceptance and policy support

College of Life Sciences, Zhejiang University, Hangzhou, PRChina *([email protected]); †these authors contributedequally to this work

Cultivated species interactions in modern agriculture WZ Ren et al.

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interactions, focusing on yield, resource use efficiency,pest control, and environmental modification. Finally, wediscuss the feasibility of incorporating positive speciesinteractions into modern agriculture for “intensificationwithout simplification” (ie achieving high and sustainablecrop yields while preserving biodiversity and minimizingnegative environmental impacts; Pearson 2007).

n Positive interactions between species in nature

In wild settings, interactions between two or more organ-isms or species may be negative (eg predation for the preyitem), positive (eg mutualism for both individuals), orneutral (eg commensalism for the unaffected actor)

(Bruno et al. 2003). Species can benefit one another bychanging the local environment (eg by reducing thermal,drought, or salt stress), by enhancing resource availability(eg where one species makes resources more available foranother, or where co-existing species use different typesof resources), and by suppressing competitive or predatorypressures (Figure 1).

Positive interactions between species – although theymay not occur in extremely stressful environments (becauseconditions therein may discourage the growth or persis-tence of both species; Holmgren and Scheffer 2010) – aremore likely to occur in stressful than in favorable environ-ments (Tirado and Pugnaire 2005; Crain 2008). For exam-ple, provision of canopy shading for neighboring plants is a

Figure 1. Species can benefit each other by: ameliorating the local environment, increasing resource availability, and providing refuges frompredation and competitors. (a) Amelioration of stress via canopy shading of neighboring plants (Gómez-Aparicio et al. 2004). Plants (redbox) grow poorly because of excessive solar radiation, high temperatures, and inadequate moisture. These stresses are reduced for the plantsgrowing under the tree canopy. (b) The burrowing activity of crabs oxygenates anaerobic marsh soils and benefits mycorrhizal fungi (inset)and plants (Daleo et al. 2007). Growth of mycorrhizal fungi and plants (red box) is weak because crabs are absent. (c) Deep-rooted plantsprovide water (blue dots) for shallow-rooted neighbors through “hydraulic lift” (Prieto et al. 2012). (d) The co-existing species sharephosphorus (P) pools (eg one species may mobilize soil organic P [yellow dots] and increase the inorganic P [purple dots] available to theirneighbors) (Turner 2008). (e) The larger plant species (Juncus roemerianus) protects the smaller plant species (Spartina alteriflora) byattracting herbivorous snails at high tide; this reduces the density of herbivorous snails on the smaller plants (Hughes 2012). S alterifloraplants are infested with more snails when growing alone (red box) than when growing with J roemerianus. (f) Under eutrophic conditions,submerged aquatic plants (macrophytes) reduce the negative effects of phytoplankton (green dots) by competing with the phytoplankton fornutrients and thereby reducing the shading caused by phytoplankton. This enhances the survival and growth of co-existing macrophytes(Bagousse-Pinguet et al. 2012). The macrophyte Potamogeton pectinatus grows better in the presence of the fast-growing macrophytePotamogeton perfoliatus than when alone (red box) because P perfoliatus reduces the shading caused by phytoplankton.

(a) (b)

(c) (d)

(e) (f)

Increase seedling survivalduring reforesting instressful environments;promote plant fitness anddistribution in restorationof marsh and tidal flats

Enhance resource useefficiency in intercroppingor agroforest systems

Reduce insect pests,diseases, and weeds inintercropping, agroforest,or rice–aquatic speciesco-culture systems

WZ Ren et al. Cultivated species interactions in modern agriculture

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primary mechanism of environmental ameliora-tion. In harsh arid habitats, seed germinationand seedling survival are often promoted underan established plant canopy as compared withcanopy-absent open areas because the presenceof “nurse plants” (ie plants that improve themicrohabitat for neighboring plant species)increases shade and helps retain soil moisture(Figure 1a; Callaway 1995; Gómez-Aparicio etal. 2004). Likewise, the burrowing activity ofcrabs oxygenates the anaerobic soils in saltmarshes, which promotes the formation of myc-orrhizae and increases plant growth (Figure 1b;Daleo et al. 2007).

Positive species interactions can alsoincrease access to limiting resources such aswater and soil nutrients. Deep-rooted plants,for instance, can provide water for shallow-rooted neighbors through “hydraulic lift”(Figure 1c; Dawson 1993; Prieto et al. 2012).Similarly, some species may mobilize soilorganic phosphorus (P), making it available tothemselves and also to neighboring plants(Figure 1d; Turner 2008).

In marine and terrestrial systems, protectionagainst herbivores (ie through “associationaldefense”) represents an advantageous speciesinteraction (Barbosa et al. 2009; Hughes 2012).As a case in point, nurse plants not only reduceabiotic stress but may also physically impede her-bivory of seedlings growing under them or serveas an attractant that draws herbivores away from seedlings(Callaway 1995). Neighboring plants in close spatial prox-imity of one another can also make it difficult for herbivoresto detect a given focal plant or may attract the predators ofseedling herbivores (Figure 1e; Barbosa et al. 2009; Hughes2012).

Reduced interspecific competition is another poten-tially beneficial interaction. Under eutrophic conditions,submerged aquatic plants (macrophytes) reduce the com-petitive effects caused by phytoplankton and thereby pro-mote the survival and growth of co-existing macrophytes(Figure 1f; Bagousse-Pinguet et al. 2012).

The interactions described above have implications foragricultural sustainability, plant restoration in harsh envi-ronments, and species conservation. Notably, plantingmixed species (grasses and legumes) resulted in greater yieldsas compared with either species planted alone (Nyfeler et al.2009), whereas the presence of nurse plants has aided in therestoration of arid areas (Gómez-Aparicio et al. 2004; Siles etal. 2008) and salt marshes (Halpern et al. 2007).

n Positive interactions between species intraditional agriculture

In contrast to those of natural ecosystems, the compo-nents of agricultural systems are controlled by farmers.

Around the world, traditional farmers have developeddiverse and locally adapted agricultural systems toenhance food security, and these systems usually dependon local species and their interactions (Altieri 2004).Over the past 20 years, various positive interactionsbetween cultivated species used in small-scale traditionalagriculture have been described in scholarly literature.Examples include the use of neighbor crops to amelioratethe environment (by reducing heat and light stress;Padilla and Pugnaire 2006), to enhance nutrient-use effi-ciency (Li et al. 2007), and to reduce pests by repulsion(Jimenez and Poveda 2009). However, three of the mostimportant examples are legume–cereal intercropping (inuplands), rice–fish co-culture (in paddy fields), and agro-forestry.

Legume–cereal intercropping

Cereals and legumes are important food crops worldwide(Figure 2a) and are therefore important components ofglobal food security. Because legumes fix nitrogen (N) andsolubilize P, they are widely used in many intercroppingsystems, especially in areas where soil quality is poor (Li etal. 2007). Legume–cereal intercropping is practiced onevery continent except Antarctica (Figure 2b), and hascontributed to local food security in many temperate and

Figure 2. Important food crops and cropping systems. (a) Annual global totalarea harvested for five food crop categories, and the proportions of coarse grainsand legumes in three decades (1980–2011). The categories follow FAOSTATexcept that legumes here include groundnuts and soybeans, which were originallycategorized as oilcrops in FAOSTAT. (b) World map depicting locations wherelegume-based intercropping (red circles), rice–fish co-culture (purple circles), andintercropped agroforestry (green circles) are practiced.

(a)

(b)

Cereals Legumes Roots and tubers

Vegetables and melons Oilcrops primary

1200

1000

800

600

Tota

l are

a ha

rves

ted

(106

ha)

1980s 1990s 2000–2011

13.44%

69.61%

14.56%

66.07%

16.76%

61.75%

1980 1990 2000 2010Year

Total area harvested

Rice–fish co-cultureIntercropped agroforestryLegume–cereal intercropping


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tropical areas (Mucheru-Muna et al. 2010). Various kindsof legume-based intercropping have been integrated intointensive organic farming in many European and Northand South American countries (Seufert et al. 2012).

To examine the effects of the co-planted legumes andcereals on the yield of each crop, we conducted a meta-analysis based on 32 published papers (WebPanel 1); effectsize was calculated as the natural log of the response ratio

R, the mean of intercropping divided by themean of monoculture (WebPanel 1). A posi-tive effect size with confidence intervals(CIs) that do not overlap zero would indicatethat the yield of the cereal or legume wasgreater with intercropping than in monocul-ture. Our results suggest that intercroppingsignificantly increased cereal yield (meaneffect size: 0.3286; CI: 0.2471–0.4028) butdid not affect legume yield (mean effect size:0.0379, CI: –0.1193–0.1887) (WebFigure 1;WebTable 1). The increase in cereal yieldwas significantly greater with pesticide use(P < 0.05) but was not influenced by the otherfive factors (ie climate, planting pattern, irri-gation, fertilization, and weed control; Figure3a; WebTable 2) (P > 0.05). For legume yield,the effect size was not influenced by pesticidesor any of the other five factors described above(Figure 3b; WebTable 3).

Although our meta-analysis indicates thatlegume–cereal intercropping significantlyincreased only cereal yield, previous studieshave provided evidence that legumes andcereals benefit each other in legume–cerealintercropping systems. Legumes benefit cerealsby N transfer and nutrient mobilization; forexample, results of 15N-labeling indicated that14–15% of the N in N2-fixing legumes couldbe transferred to intercropped cereals (Labergeet al. 2011; Isaac et al. 2012). Legumes can alsoenhance cereal acquisition of P becauselegumes mobilize insoluble P, which is used byboth the legumes and the cereals (Hinsinger etal. 2011). Yet cereals can benefit legumes bypromoting N fixation because N transfer fromlegumes to cereals can prevent nitrate–Naccumulation in soil, which inhibits N fixa-tion by legumes (Schipanski and Drinkwater2012). Studies have also shown that cerealscan promote legume yield by increasing ironavailability, which further enhances N fixa-tion (Zuo et al. 2004).

Rice–fish co-culture

The raising of fish in rice fields has a longhistory in Asia and is still practiced in sev-eral countries worldwide, including Egypt,

India, Indonesia, Thailand, Vietnam, the Philippines,Bangladesh, and Malaysia (Figure 2b; Frei and Becker2005). The rice–fish co-culture system, which has beenmaintained for more than 1200 years in southern China,was designated in 2005 as a “globally important agricul-tural heritage system” by the United Nations (UN) Foodand Agriculture Organization, the UN DevelopmentProgramme, and the Global Environment Facility.

(a)

(b)

Figure 3. Estimated responses of (a) cereal yield and (b) legume yield to intercropsunder various climate types, planting patterns, and management levels. Circles areeffect sizes as lnR with bootstrap confidence intervals (CIs) calculated from 999iterations (see WebPanel 1). Where CIs do not overlap zero and are positive,legume or cereal yield was higher with intercropping than with monoculture. WhereCIs between the two effect sizes do not overlap, the effect sizes differ significantly.Numbers above the circles indicate the number of studies. Aw (equatorial andwinter dry), BSh (arid: steppe and hot arid), BWk (arid: desert cold arid), Cfa(warm temperate: high humidity and hot summer), Cfb (warm temperate: highhumidity and warm summer), Cwa (warm temperate: desert and hot summer),Cwb (warm temperate: desert and warm summer). R and M (rowed and mixedintercropping, respectively); No-I and I (without and with irrigation, respectively);No-F and F (without and with chemical fertilization, respectively); No-P and P(without and with pesticide, respectively); No-W, W1, and W2 (without weeding,weeded by hand, and weeded by herbicide, respectively).


Our meta-analysis of 12 research papers publishedwithin the past 20 years (WebPanel 2) indicates thatrice–fish co-culture has a positive effect on rice yield,regardless of fish culture type (ie single fish species ormixed fish species) (Figure 4; WebTable 4; WebTable 5).The analysis of the published literature also revealed thatlower amounts of pesticides and chemical fertilizers wereused in rice–fish co-culture than in rice monoculture. Onestudy involving 120 farms in Vietnam showed that totalapplication of fungicides, herbicides, and insecticides wasreduced by 44% in rice–fish farming as compared with ricemonoculture (Berg 2002), while in Indonesia, no herbi-cides were applied in rice–fish co-culture and pesticide usewas only 23% of that used in rice monoculture (Dwiyanaand Mendoza 2006). A 6-year field survey and 5-year fieldexperiment in southern China indicated that rice–fish co-culture produced the same yield and yield stability as ricemonoculture but with 68% less pesticide and 24% lesschemical N fertilizer (Xie et al. 2011).

The presence of fish increases rice yields through pest,disease, and weed control (where pesticide use is limited);for instance, the abundance of herbivorous planthopperswas 30–60% lower when fish were present than in ricemonoculture (Frei and Becker 2005). Xie et al. (2011)demonstrated that fish were directly responsible for 26%of this reduction. Fish can also disrupt or consumemycelia of the pathogenic fungus Rhizoctonia solani andthus inhibit the development of rice sheath blight. Fishin rice fields also uproot and eat weedy species (Frei andBecker 2005). At the same time, rice plants benefit fishby providing both physical refuge and insect herbivores asa food supply.

The reduction of fertilizer use in rice–fish co-culture mayresult from complementary use of N by rice and fish. Onefield experiment demonstrated that rice plants use theunconsumed N in fish feed (31.8% of the N contained inrice grain and straw was from fish feed; Xie et al. 2011). Fishmay also enhance soil nutrient availability and N uptakeby rice plants (Panda et al. 1987; Oehme et al. 2007).

Agroforestry

We use the term agroforestry here to refer to land-use sys-tems and practices in which woody perennials are delib-erately integrated with crops on the same land-manage-ment unit. This type of agroforestry is practicedworldwide (Figure 2b) and contributes to local food pro-duction, the local economy, and biodiversity conserva-tion (De Beenhouwer et al. 2013).

According to the reviewed literature (WebPanel 3),crop yields substantially increased in some intercroppedagroforestry systems (WebTable 6). In such systems,woody perennials benefit the annual crops by ameliorat-ing the microclimate under arid conditions (Du et al.2010), by providing water through hydraulic lift(Droppelmann et al. 2000), and by providing nutrientsand improving soil fertility (Suresh and Rao 2000).

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Woody perennials, however, can also have negativeeffects on their annual neighbors (eg shading and rootcompetition; Reynolds et al. 2007), resulting in reducedcrop yields (WebTable 6). These negative effects can bediminished by selecting deep-rooted tree species, plantingcrops and trees at an appropriate distance, and pruningthe shoots and lateral roots of the trees (WebTable 7).

n Using positive species interactions to achievesustainability in modern agriculture

Although beneficial outcomes of interspecific interac-tions may be promoted by optimizing crop–crop partner-ships, rice–fish partnerships, or crop–tree pairings in agri-culture, the reported effects vary among studies. Thisvariability occurs because species interactions are sensi-tive to environmental conditions, planting techniques,and management approaches. Such systems thereforerequire not only compatible planting strategies but alsoprogressive policies to encourage their adoption by farm-ers and to increase societal acceptance (Figure 5).

Planting strategies

Planting strategies that will support the use of positivespecies interactions in modern agriculture include a care-ful selection of the partner species and the concomitantdevelopment of compatible field structure and configura-tion, machinery, and field management.

The selection of partners is critical, given that intro-ducing a species into a monoculture does not guaranteepositive effects. Competition or other negative interac-tions may occur simultaneously with facilitation whentwo species occur in the same area (Omer et al. 2007).Encouraging positive effects and avoiding negative effects

Figure 4. Estimated responses of rice yield to rice–fish co-culture with a single fish species or mixed fish species. Effect sizesare weighted means ± standard error (SE) (see WebPanel 2).Effect sizes with positive values indicate a greater yield of rice inco-culture than in monoculture. Numbers above circles indicatethe numbers of studies.


depend on finding the appropriate interacting partners.For example, positive interactions may occur in an inter-cropping system when the partners: (1) differ in shootand root growth so that their use of above- and below-ground resources is complementary; (2) differ in sensitiv-ity to (both biotic and abiotic) environmental stresses,such that the stress-tolerant species can provide “refuge”for the non-tolerant one; (3) differ in their ability to uti-lize soil nutrients (so that they share the entire pool ofavailable nutrients); or (4) promote neighboring plantsvia allelobiosis, in which one plant releases chemicalsthat benefit the co-existing partners.

In traditional agriculture, positive interactions betweenspecies are typically used on a small scale by local farmers(Altieri 2004). Yet the use of positive species interactionswithin the context of large-scale modern agriculture willrequire compatible field structure and configuration, andspecialized machinery. For instance, field trenching andridging techniques for land preparations are often differ-ent in intercropping systems as compared with monocul-ture systems because the two intercropped species maydiffer in shoot and root growth. Machines suitable fortrenching, ridging, sowing, and harvesting in intercrop-ping systems need to be designed if these systems are tooperate efficiently over large areas. In addition, if the twospecies have different irrigation or fertilization require-ments, technologies for co-delivery of these resourcesneed to be developed. When fish or other aquatic animalsare introduced into paddy fields, temporary physical refu-gia (eg trenches and pits) must be provided to betterensure their protection during field operations and to pre-

vent their escape. Traditional co-culture systems are usu-ally carried out on a small scale, and refugia construction,feed broadcasting, rice transplanting and harvesting, andother farming activities are often performed manually.For large-scale co-cultivation of rice and fish, however,these and other operations require machinery.

In modern agricultural systems, knowledge-based andintegrated field management (including irrigation, pestcontrol, and fertilization) can increase yield while reduc-ing environmental damage (Chen et al. 2011). For mono-cultures (Figure 5a), information concerning manage-ment (eg nutrient and water requirements, pest control)can be obtained and implemented with relative easebecause only one crop is produced. Intercropping or co-culture systems (Figure 5b), in contrast, require informa-tion about both species, and about how they interact witheach other and with the surrounding environment.

Farmer incentives, societal acceptance, and policies

Because farmers implement practices that foster agricul-tural development, incentives are important for promot-ing the use of positive interactions between cultivatedspecies. Current incentives tend to favor increased agri-cultural production over ecosystem services (ie farmersare rewarded for using high-yielding varieties, chemicalfertilizers, and pesticides; Tilman et al. 2002). Eventhough farmers often benefit directly from increasedyields and from selected ecosystem services (eg naturalpest control, less nutrient runoff) when positive speciesinteractions are integrated into modern agricultural prac-

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Figure 5. Design for the sustainable intensification of agriculture based on the integration of positive interactions between cultivatedspecies into modern intensive agriculture. (a) Monoculture; (b) intercropping or co-culture.

(a)

(b)

Partnership selection

Field construction and machinery

Field management

Considering the needsand characteristics ofthe two species

Considering food yields,consumer incentives, andlow chemical inputs

Market incentives

Social acceptability


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tices, oftentimes these benefits may not be sufficient tooffset the increased labor costs (Chen and Tang 2013). Inaddition, farmers do not benefit financially from unseenbut vital ecosystem services (eg water purification, carbonsequestration, pollution mitigation) that are important tothe public. Integrating the public benefits obtained fromimproved ecosystem services into a financial reward sys-tem for farmers is important in encouraging farmers to usepositive species interactions in modern agriculture.However, this will require appropriate policy support.Public financial compensation, usually from a local gov-ernmental organization, is commonly used to encouragenew and more environmentally friendly farming practices(eg organic agriculture, conservation tillage; Kurkalova etal. 2006; Jansky and Zivelova 2007). For example, a sys-tem of “payments for ecosystem services” (PES; Jack et al.2008) has been successfully used in the UK and in CostaRica to promote conservation practices (Dobbs andPretty 2008; Garbach et al. 2012). Encouraging farmers toincorporate co-culture of species using a PES system is apromising start, but further studies are needed to helplocal people implement this planting strategy successfully.Other policies (eg establishing a tax on chemical fertiliz-ers and pesticides, or removing subsidies for these inputsto discourage their excessive use) have been applied toenhance organic agriculture in Europe (Bahrs 2005) andmight also encourage the use of co-cultured species.

The integration of positive species interactions intomodern agriculture will also depend on consumer incen-tives and societal acceptance. Food costs and nutritionalquality have traditionally influenced consumer choices(van Rijswijk and Frewer 2008; Steenhuis et al. 2011).Members of the general public are beginning to pay moreattention to environmental concerns, particularly if thesecan be linked to preferences (eg better tasting vegetables)or health (eg lower pesticide use). These trends can pro-mote the societal acceptance of co-cultured products, butsuch acceptance may also require policy support to ensurea stable supply.

n Conclusions

Species have evolved a variety of positive interactionsthat enable them to optimize resources and to survive invariable or harsh environments; these positive interac-tions result in the co-existence of diverse species, and thedelivery of high ecosystem productivity and stability(Cardinale et al. 2002; Bruno et al. 2003; Tirado andPugnaire 2005). Modern agriculture can therefore har-ness existing knowledge of species–species interactions,derived from natural ecosystems research, to improve andoptimize production strategies. Several traditional agri-cultural practices have already successfully harnessedlocal species diversity and their interactions for food pro-duction (Altieri 2004). However, the successful applica-tion of these positive interactions in modern agriculturewill require policies that provide farmer incentives and

compatible programs that promote societal acceptance ofthese ecologically based strategies. In the near future,agriculture may attain “utopic sustainability” in food pro-duction, where high and sustainable yields are achievedwith negligible to minimal negative environmentalimpacts (Pearson 2007; Kremen et al. 2012).

n Acknowledgements

This research was supported by the National BasicResearch Program of China (No 2011CB100406) andthe National Science Foundation of China (No31270485).

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Can positive interactions between cultivated species help to sustain modern agriculture?