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Species interactions incrop communities

EKOLOGI PERTANIAN

Fakultas Pertanian, Universitas Brawijaya

Toto Himawan


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COMMUNITY:

Formed by a complex of interactingpopulations of crops, weeds, insectsand microorganisms.


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Introduction

Emergent qualities = characteristics of community, important ina systems stability, productivity and dynamic function

Research typically focused on crop population rather thancommunity of which it is a part

Lose ability to consider manipulating the community interactionsto benefit cropping system

Only detrimental interactions have been considered (weeds, pestherbivores, disease)

Conventional approach minimizes interactions vs. agroecologicalapproach which attempts to understand species interactions inthe context of the larger community


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Interference at thecommunity 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 morecomplete understanding of the mechanisms of interaction

Ways in which interference may combine to effect cropcommunity


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Modes of interference underlying

species interaction in communities

INTERFERENCE

Allelopathy

Food source forbeneficials

Competition

Parasitism

Herbivory

Mutualism

Microhabitat

modification

Addition impact Removal impact

Combined removal and addition


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Complexity of interactions:

Interactions are complex and difficult to

discern

Grass - clover example


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Coexistence:

Populations of similar organisms often share the samehabitat 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 allowcoexistence will help us design multiple crop

communities Combine species with slightly different physiological

characteristics or resource needs to promotecoexistence


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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)


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Mutualism:

Facultative mutualisms = all members cansurvive alone but benefit from interaction

Often mutualisms help species avoid somenegative impact

Increase resistance of entire system tonegative impacts of pests, diseases and weeds


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Mutually Beneficial Interferencesat Work in Agroecosystems

Beneficial Interferences of Cover Crops:

Beneficial Interferences of Weeds:

Intercropping :


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Beneficial Interferences of CoverCrops :

Cover crop = plant species (usually grasses or legumes)grown in pure or mixed stands to cover the soil of the cropcommunity 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 soilfertility; suppress weeds, insects, and pathogens (see Table15.1 for more benefits)

May be beneficial at some times while detrimental at others(see CASE STUDY rye/bellbeans)


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Beneficial Interferences of Weeds :

With proper management, weeds can serve role ofcover crop

Modification of the Cropping SystemEnvironment

Control of Insect Pests by Promotion ofBeneficial Insects


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Modification of the Cropping SystemEnvironment

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


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Control of Insect Pests by Promotion ofBeneficial Insects

Certain weeds should be regarded asimportant components of the crop communitybecause of the positive effects they have onpopulations of beneficial insects


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Intercropping:

Two or more crops planted together may reduce needfor 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


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Using Species Interactions forSustainability

Challenge for agroecologists is to putecological understanding into the context ofsustainability

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