organic farming, higher local and landscape complexity ... · landscape factor species richness...

Organic farming, higher local and landscape complexity improve

arthropod predator species richness and abundance in orchards

Alistair Galloway

Department of Conservation Ecology & Entomology

Stellenbosch University

Supervisor: Dr James Pryke

Co-supervisors: Dr René Gaigher and Dr Colleen Seymour

1. INTRODUCTION

Impacts of global agricultural growth

Native habitat destruction Chemical applications

Leads to ↓ biodiversity and ecosystem functioning

Functional diversity and ecosystem functioning

1. INTRODUCTION

Ecosystem

functioning

A functional type,

e.g. predators

Benefits of organic agriculture for arthropod predators

No pesticide and fertilizer usage + groundcover +

habitat heterogeneity

= ↑ arthropod predator complex

1. INTRODUCTION

Conserving non-crop habitat in the agricultural landscape

1. INTRODUCTION

↑ arthropod predator diversity and abundance

Agrobiodiversity research, particularly of predators:

• ↑ in developed, transformed countries and ↓ in

developing, biodiverse countries

• ↑ in annual cropland and ↓ in perennial

cropland

STUDY AIM

To investigate what impact different citrus farming

management types within different landscape

contexts have on the arthropod predator

complex.

1. INTRODUCTION

STUDY OBJECTIVES

To determine:

1. differences between predator species

richness, abundance, diversity and

assemblage composition of organic and

conventional citrus orchards with and without

neighbouring natural vegetation (NV).

2. which environmental variables drive the

observed arthropod predator patterns.

1. INTRODUCTION

• 36 study sites on 15 citrus farms – Sundays River Valley,

Eastern Cape, South Africa

• Albany Alluvial Vegetation, Sundays Noorsveld and

Sundays Thicket

• Albany Centre of Floristic Endemism and Maputaland-

Pondoland-Albany Biodiversity Hotspot

2. METHODS

Study site structure

Natural

vegetation

Natural

vegetation

Organic

orchard

(with NV)

Conventional

orchard

(with NV)

Organic

orchard

(without NV)

Conventional

orchard

(without NV)

2. METHODS

X 6 X 6 X 6

X 6 X 6 X 6

2. METHODS

Arthropod predator sampling

Ground level

2. METHODS

Lower canopy Upper canopy

Arthropod predator sampling

Environmental variable sampling

• Plant species richness, abundance, average height

& number of flowering plants

• % vegetation cover, ground cover & average leaf

litter depth

2. METHODS

At each sampling point:

• 50 lower and 50 upper vacuum insertions

• 2 pitfall traps

• 1 m² and 5 m² quadrats

40 m 45 m 50 m

― Pitfall

— Quadrat

— Vacuum walk

2. METHODS

Distance from site edge

50 m

5 m

2. METHODS

Sample sorting in the lab

2. METHODS

Data analyses included:

• Total arthropod predator species and the four

major predator groups (ants, beetles, spiders

and wasps) – LMM’s

• Management types (organic vs conventional)

• Biotopes (orchards with NV vs orchards

without NV vs NV)

• Treatment types (organic & conventional

orchards with and without NV, NV

neighbouring organic and conventional

orchards)

3. MAIN RESULTS

Management type comparisons

Biotope comparisons

3. MAIN RESULTS

Predator

grouping

Landscape

factor

Species richness Abundance

Main test Post hoc Main test Post hoc

Total

Management 11.34*** Org > Conv 10.81** Org > Conv

Biotope 4.12 - 0.97 -

Ant

Management 2.46 - 9.63** Org > Conv

Biotope 16.48*** OrchNV < NV, Orch < NV 3.00 -

Beetle

Management 11.25*** Org > Conv 6.80** Org > Conv

Biotope 57.71***OrchNV > NV, Orch > NV,

OrchNV > Orch42.69***

OrchNV > NV, Orch > NV

Spider

Management 7.96** Org > Conv 8.68** Org > Conv

Biotope 2.74 - 1.96 -

Wasp

Management 8.93** Org > Conv 5.76* Org > Conv

Biotope 9.93**OrchNV > NV,

OrchNV > Orch10.84**

OrchNV > NV, OrchNV > Orch

3. MAIN RESULTS

Predator

grouping

Landscape

factor

Species richness Abundance

Main test Post hoc Main test Post hoc

Total

Management 11.34*** Org > Conv 10.81** Org > Conv

Biotope 4.12 - 0.97 -

Ant

Management 2.46 - 9.63** Org > Conv

Biotope 16.48*** OrchNV < NV, Orch < NV 3.00 -

Beetle

Management 11.25*** Org > Conv 6.80** Org > Conv

Biotope 57.71***OrchNV > NV, Orch > NV,

OrchNV > Orch42.69***

OrchNV > NV, Orch > NV

Spider

Management 7.96** Org > Conv 8.68** Org > Conv

Biotope 2.74 - 1.96 -

Wasp

Management 8.93** Org > Conv 5.76* Org > Conv

Biotope 9.93**OrchNV > NV,

OrchNV > Orch10.84**

OrchNV > NV, OrchNV > Orch

3. MAIN RESULTS

Treatment type comparisons

Conventional & Organic

orchards without NV

Conventional & Organic

orchards with NV

3. MAIN RESULTS

Total arthropod predators

Species richness Abundance

C CNV NVC O ONV NVO

Treatment type

C CNV NVC O ONV NVO

Treatment type

3. MAIN RESULTS

Ant

Abundance

C CNV NVC O ONV NVO

Treatment type

3. MAIN RESULTS

Beetle

Species richness

C CNV NVC O ONV NVO

Treatment type

C CNV NVC O ONV NVO

Treatment type

Abundance

3. MAIN RESULTS

Species richness Abundance

Spider

Species richness Abundance

C CNV NVC O ONV NVO

Treatment type

C CNV NVC O ONV NVO

Treatment type

3. MAIN RESULTS

Species richness Abundance

Wasp

Species richness Abundance

C CNV NVC O ONV NVO

Treatment type

C CNV NVC O ONV NVO

Treatment type

3. MAIN RESULTS

Environmental variable drivers

of predator patterns

3. MAIN RESULTS

Landscape factor Response variable Environmental variables

CombinationSpecies richness (+) APH 1: 6.44*, (+) ALLD 5: 5.04*

Abundance (+) APH 1: 5.24*, (–) ACL 5: 6.48*

Management

type

OrgSpecies richness (–) ACL 5: 7.79**, (+) ALLD 5: 10.36**

Abundance (–) ACL 5: 15.07***, (–) ALLD 5: 10.49**

ConvSpecies richness (+) APH 1: 8.01**, (+) TFP 5: 4.34*, (+) ACH 5: 14.14***

Abundance -

Biotope

OrchNVSpecies richness (+) APH 1: 5.95*, (+) ACH 5: 5.93*

Abundance (+) PSA 1: 12.28***

OrchSpecies richness (+ Org, – Conv) MNG: 9.97**, (+) ACG 5: 8.24**

Abundance (+) ALLD 5: 21.12***

NVSpecies richness (+) TFP 5: 4.52*, (+) ACG 5: 7.63**

Abundance (–) ALLD 5: 8.22**

Total arthropod predators

3. MAIN RESULTS

Average plant height – lower canopyAverage % herb cover

Average leaf litter depthAverage % grass cover

Plant species abundance – lower canopy

+

4. DISCUSSION

• This study contributes to the growing body of

literature worldwide on the impact of local and

landscape factors on the arthropod predator

complex

• Predator-friendly farming practices and conserving natural vegetation can ↑ predator

species richness and abundance

• Organic farming ↑ predator species richness

and abundance – ↑ environmental heterogeneity

of the understorey

4. DISCUSSION

• Conventional orchards had a greater

improvement in predator species richness

associated with nearby NV than organic

orchards

• Natural vegetation ↑ landscape complexity and

↑ predator species richness in conventional

orchards

4. DISCUSSION

• In comparison, organic orchards with and

without neighbouring natural vegetation

generally did not differ

• The ↑ environmental heterogeneity provided by

neighbouring natural vegetation did not influence predators - already ↑ environmental

heterogeneity present

• Organic farming ↑ predator species richness

and abundance in simpler landscapes

(intermediate landscape-complexity hypothesis)

5. CONCLUSION

To ↑ predator species richness and abundance:

• Farmers should aim to diversify both 1) local-

and 2) landscape-level environmental

heterogeneity

1) Cover cropping, mulching and the use of

organic compost and manure in orchards

2) Conserving and restoring remnant natural

vegetation in the landscape

ACKNOWLEDGEMENTS

• My supervisors – Dr James Pryke, Dr René Gaigher and Dr

Colleen Seymour

• My funders – South African National Biodiversity Institute

(SANBI), Stellenbosch University and Ernst & Ethel Eriksen Trust

• The Sundays River Citrus Company (SRCC), particularly Andre

Combrink, and affiliated farmers

• The Sundays Organic Growers Association (SOGA) farmers and

managers

• Stephan Gericke and Oliver Hansen for their field assistance

• Liesel Kets, Adionah Chiomadzi, Alheit du Toit and Alexander

Heiberg for their laboratory assistance

CONTACT DETAILS

Alistair Galloway

email address: alistair.d.galloway@gmail.com