Species interactions in crop communities EKOLOGI PERTANIAN Fakultas Pertanian, Universitas Brawijaya EKOLOGI PERTANIAN Fakultas Pertanian, Universitas Brawijaya Toto Himawan

COMMUNITY:  Formed by a complex of interacting populations of crops, weeds, insects and microorganisms.

IntroductionIntroduction  Emergent qualities = characteristics of community, important in a system’s stability, productivity and dynamic function  Research typically focused on crop population rather than community of which it is a part  Lose ability to consider manipulating the community interactions to benefit cropping system  Only detrimental interactions have been considered (weeds, pest herbivores, disease)  Conventional approach minimizes interactions vs. agroecological approach which attempts to understand species interactions in the context of the larger community  Emergent qualities = characteristics of community, important in a system’s stability, productivity and dynamic function  Research typically focused on crop population rather than community of which it is a part  Lose ability to consider manipulating the community interactions to benefit cropping system  Only detrimental interactions have been considered (weeds, pest herbivores, disease)  Conventional approach minimizes interactions vs. agroecological approach which attempts to understand species interactions in the context of the larger community

Interference at the community level  removal - removal of some resource by one or both of the interacting organisms  addition - one or both organisms adds some substance or structure to the environment 2 types of interference : Advantage of interference approach is that it allows a more complete understanding of the mechanisms of interaction Ways in which interference may combine to effect crop community

Modes of interference underlying species interaction in communities INTERFERENCE Allelopathy Food source for beneficials Competition Parasitism Herbivory Mutualism Microhabitat modification Addition impactRemoval impact Combined removal and addition

Complexity of interactions:  Interactions are complex and difficult to discern  Grass - clover example  Interactions are complex and difficult to discern  Grass - clover example

Coexistence :  Populations of similar organisms often share the same habitat even though niches highly overlap  Ecologists widely accept the idea that selection for coexistence may be the rule more than the exception  Many domesticated species have evolved in polycultures  Understanding mechanisms of interference that allow coexistence will help us design multiple crop communities  Combine species with slightly different physiological characteristics or resource needs to promote coexistence  Populations of similar organisms often share the same habitat even though niches highly overlap  Ecologists widely accept the idea that selection for coexistence may be the rule more than the exception  Many domesticated species have evolved in polycultures  Understanding mechanisms of interference that allow coexistence will help us design multiple crop communities  Combine species with slightly different physiological characteristics or resource needs to promote coexistence

Mutualism : 3 Types:  Inhabitational - one mutualist lives wholly or partly inside the other (eg. Rhizobium bacteria and leguminous plants)  Exhabitational - organisms are relatively independent physically, but interact directly (eg. flowering plant and its insect pollinator)  Indirect - interactions among a set of species modify the environment in which they all live to the benefit of the mixture; involve more than 2 species (eg. polyculture agroecosystem) 3 Types:  Inhabitational - one mutualist lives wholly or partly inside the other (eg. Rhizobium bacteria and leguminous plants)  Exhabitational - organisms are relatively independent physically, but interact directly (eg. flowering plant and its insect pollinator)  Indirect - interactions among a set of species modify the environment in which they all live to the benefit of the mixture; involve more than 2 species (eg. polyculture agroecosystem)

Mutualism : Facultative mutualisms = all members can survive alone but benefit from interaction Often mutualisms help species avoid some negative impact Increase resistance of entire system to negative impacts of pests, diseases and weeds

Mutually Beneficial Interferences at Work in Agroecosystems Beneficial Interferences of Cover Crops: Beneficial Interferences of Weeds : Intercropping :

Beneficial Interferences of Cover Crops :  Cover crop = plant species (usually grasses or legumes) grown in pure or mixed stands to cover the soil of the crop community for part or all of the year  Green manure = cover crop tilled into the soil to add OM  Living mulch = cover crop grown directly with other crops  Reduce soil erosion; improve soil structure; enhance soil fertility; suppress weeds, insects, and pathogens (see Table 15.1 for more benefits)  May be beneficial at some times while detrimental at others (see CASE STUDY rye/bellbeans)

Beneficial Interferences of Weeds : With proper management, weeds can serve role of cover crop  Modification of the Cropping System Environment  Control of Insect Pests by Promotion of Beneficial Insects

Modification of the Cropping System Environment  Weeds protect soil surface from erosion  take up nutrients that might otherwise be leached  add OM  selectively inhibit development of more noxious species through allelopathy

Control of Insect Pests by Promotion of Beneficial Insects  Certain weeds should be regarded as important components of the crop community because of the positive effects they have on populations of beneficial insects

Intercropping :  Two or more crops planted together may reduce need for external inputs  Mostly used in the tropics  Corn-bean-squash polyculture example  - growing 3 crops together gave higher total yield  - LER>1 Understanding ecological foundation of the interactions in polycultures is key to returning its prominence to agriculture

Using Species Interactions for Sustainability  Challenge for agroecologists is to put ecological understanding into the context of sustainability