B4.2.9 Adaptations of herbivores for feeding on plants and of plants for resisting herbivory Notes

Herbivores Have Unique Adaptations to Exploit Plants As A Food Source

1. Herbivores are animals that feed exclusively on plants.
2. To adapt to this diet, herbivores possess specialized structural features for processing plant material.

Two Main Groups of Herbivores

1. Most insects are herbivores and can be classified into two main groups based on their feeding strategies:
   1. Chewing Herbivores
      1. Examples: Beetles and other insects with jaw-like mouthparts.
      2. Feeding Mechanism: These insects bite off, chew, and ingest pieces of leaf material.
   2. Sap-Feeding Herbivores
      1. Examples: Aphids and other insects with tubular mouthparts.
      2. Feeding Mechanism: They pierce plant tissues to reach phloem sieve tubes and feed on nutrient-rich sap.

Note

Aphids rely on their sharp tubular mouthparts to extract sap from plants, which they metabolize for energy and growth.

Plant Defenses Against Herbivory

Plants have evolved various strategies to deter herbivores and reduce damage.

1. Physical Defenses

1. Spines and Thorns: Sharp structures that can injure herbivores.
2. Smooth, Waxy Surfaces: These can make it harder for insects to grip leaves.

Example

The tree nettle (Urtica ferox) has stinging hairs that inject irritating substances.

2. Chemical Defenses

1. Plants produce secondary metabolites, which are toxic or deterrent compounds.
   1. Primary Metabolites: Substances essential for basic metabolic functions (e.g., proteins, carbohydrates).
   2. Secondary Metabolites: Defensive chemicals not directly involved in metabolism.

1. Herbivores face a nutritional challenge, plant material is often tough, fibrous, and chemically defended. To overcome this, herbivores have evolved specialized feeding structures and digestive systems.

Herbivore Counter-Adaptations

1. Some herbivores have evolved metabolic adaptations to counteract plant defenses.
2. Detoxification Enzymes: Herbivores can neutralize toxic compounds produced by plants. Certain insects metabolize alkaloids, making them immune to the chemical defenses of their host plants.
3. Specialized Feeding Habits: Many herbivores feed on specific plants, leading to plant-herbivore specificity. This results in a co-evolutionary relationship where both plants and herbivores develop traits to outcompete each other.