Species interactions in crop communities

1. Species interactions in crop communities Toto Himawan EKOLOGI PERTANIAN FakultasPertanian, UniversitasBrawijaya

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

3. Introduction • 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

4. Interference at the community level 2 types of interference : • 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 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

5. Addition impact Removal impact Combined removal and addition

6. Complexity of interactions: • Interactions are complex and difficult to discern • Grass - clover example

7. 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

8. 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. polycultureagroecosystem)

9. Mutualism :

10. Mutually Beneficial Interferences at Work in Agroecosystems

11. 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)

12. 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

13. 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

14. 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

15. 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

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