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