Spines protect plants against browsing by small climbing mammals

Area of Science:

• Ecology
• Plant-animal interactions
• Mammalogy

Background:

• Spines on woody plants are known defenses against large mammalian browsers.
• It is unclear if spines deter smaller, arboreal mammals that forage within plant canopies.

Purpose of the Study:

• To investigate if plant spinescence deters small mammals, specifically southern plains woodrats (Neotoma micropus), from accessing food resources.
• To determine the effectiveness of spines as a defense mechanism against rodent foraging within shrub canopies.

Main Methods:

• Raisins were offered on blackbrush (Acacia rigidula Benth.) branches with varying degrees of spinescence.
• Southern plains woodrats were habituated to humans and allowed to forage for raisins on naturally spineless, moderately spiny, very spiny, and spine-removed branches.
• Foraging efficiency was measured by the woodrats' ability to access the raisins.

Main Results:

• Plant spinescence significantly reduced woodrat foraging efficiency (P=0.0001).
• Branches with higher spinescence presented greater challenges to woodrats attempting to reach the raisins.
• Spines, not just the physical structure of the branches, were a key deterrent.

Conclusions:

• Plant spines serve as an effective defense against browsing by small, arboreal mammals, in addition to their known role against large herbivores.
• Spines may play a broader role in plant defense strategies across different mammalian herbivore guilds.
• This research expands our understanding of the ecological functions of plant physical defenses.