Landscape distribution patterns Foraging are hierarchical in - - PowerPoint PPT Presentation

Motivation for study

• Large herbivore grazing

distribution patterns are hierarchical in nature

– varying organisation levels of forage selection

• Finer-scale studies are

needed

– Herbivore response to greenness

Landscape

Foraging area

Feeding patch

Feeding station Bite

Senft et al. 1987 & Bailey et al. 1996

Objectives

• Objective 1:

– To determine whether zebra select for the greener grass tufts within feeding stations

• Objective 2:

– To determine whether zebra select for the greener feeding stations within a foraging area

DRINKING RESTING RESTING EATING EATING

FORAGING AREA

Feeding Patch

FEEDING PATCH

Study area

Manyeleti Game Reserve

GRASS TUFT SELECTION

Objectives & Hypotheses

• Objective 1:

– To determine whether zebra select for the greener grass tufts within feeding stations

• Hypothesis

– Zebra are selective and select for greener tufts of grass. – Zebra select for certain species – Zebra select for the greener species

• Binary response variable

– Grazed / non-grazed

• Explanatory variables

– Greenness categories according to Walker scale – Individual species

• Themeda triandra
• Panicum maximum
• Digiteria eriantha
• Urochloa mosambicensis
• ‘Other’
• Change over Season
• Mid dry

(Aug – Sep 2010)

• Late dry

(October 2010)

• Early wet

(November 2010)

Data Analysis

Model Selection

• Logistic regression
• Response variable

– Grazed/Non-grazed

• Best model (AICc)

– Species X Greenness & Species X Season – Estimated coefficients – Log-odd ratios

Greenness

Species

Interaction: Species vs Greenness

Interaction: Species per Season

FEEDING STATION SELECTION

• Objective 2:

– To determine whether the zebra select for the greener feeding stations within the foraging area

• Hypothesis

– Within a foraging area, zebra select feeding stations that are greener – The presence of certain grass species increases the selection of a feeding station – The presence of certain grass species together with the greenness of the feeding station during a specific season increase selection of a feeding station

Objectives & Hypotheses

Data Analysis

• Binary response variable

–Grazed / non-grazed

• Explanatory variables

–NDVI values ‘Greenness’ –Absence/presence of Individual grass species –Change over Season

Feeding station Greenness

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100

< 0.2 0.3 - 0.39 0.4 - 0.49 0.5 - 0.59 > 0.6

Availability grazed (%)

Availability of feeding stations (%) NDVI Values

Mid dry

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100

< 0.2 0.3 - 0.390.4 - 0.49 0.5 - 0.59 > 0.6

NDVI Values Availability grazed (%) Availability of feeding stations (%)

Late dry

Model Selection

• Logistic regression
• Response variable:

– Grazed/Non-grazed

• Best model:

– NDVI X Individual Species & Season X Individual Species – Estimated coefficients – Log-odd ratios

Interaction: Greenness vs Species

Key points

• Zebra selection was not consistent across

scales

• Grass tuft selection was based on:

– A combination of both species and greenness – Will eat less palatable species if the greenness is higher

• Feeding station selection is based on:

– NOT Species – Greenness

Conclusion

• At grass tuft level

– Zebra select towards greenness

• Feeding station:

– No strong pattern – Man-made organisation level – Grass tuft level ?? – Landscape level??

• Further studies are needed at the larger scales to be able to

compared

However....

Landscape Foraging area

Feeding patch

Feeding station Bite

Thank you

Acknowledgments:

• Supervisors:
• Dr F Parrini
• Dr B Erasmus
• Manyeleti Game

Reserve

• National Research

Foundation

Grass Tuft Greenness

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100

1-10 11-25 26-50 51-90 Grass tufts grazed (%) Available grass tufts (%)

Greenness (%) Available % Grazed %