Winning by a neck: tall giraffes avoid competing with shorter browsers

Area of Science:

• Ecology
• Zoology
• Evolutionary Biology

Background:

• Giraffes exhibit a vertically elongated body form, typically feeding at higher canopy levels than other savanna browsers.
• This feeding height may be influenced by resource availability and competition with smaller herbivores.

Purpose of the Study:

• To experimentally investigate the role of interspecific competition in driving giraffe foraging behavior.
• To test the hypothesis that giraffes' high browsing preference is an adaptation to avoid competition.

Main Methods:

• Exclosures were used to exclude giraffes from specific Acacia nigrescens trees in South Africa's Kruger ecosystem.
• Leaf biomass per shoot was compared across different height zones in both excluded and control trees after a growing season.

Main Results:

• No significant differences in leaf biomass per shoot were found across height zones in trees protected by exclosures.
• Control trees (accessible to giraffes) showed significant differences in leaf biomass, indicating selective browsing at lower levels.

Conclusions:

• Giraffes' preference for high-level browsing is likely driven by competition with smaller browsers, leading to resource partitioning.
• This study provides experimental evidence supporting the evolutionary hypothesis that giraffe body elongation is a result of competition within browsing ungulates.