Constitutive defenses

Definition

Constitutive defenses are the physical and chemical traits that plants develop as a permanent means of protection against herbivores and pathogens. These defenses are always present in the plant and do not require the presence of a threat to be activated. Such traits include tough leaves, thorns, and the production of toxic compounds, which deter potential attackers consistently throughout the plant's life cycle.

5 Must Know Facts For Your Next Test

1. Constitutive defenses are genetically programmed traits that can vary among different plant species, adapting to their specific environments and herbivore pressures.
2. Examples of constitutive defenses include physical barriers like thick bark and mechanical structures like spines or trichomes that physically deter herbivores.
3. Chemical constitutive defenses can involve toxic alkaloids or phenolic compounds, which can inhibit digestion or cause harm to herbivores upon ingestion.
4. These defenses often come with a trade-off, as investing resources into constitutive defenses may limit a plant's ability to grow or reproduce quickly.
5. Constitutive defenses can also influence plant-animal interactions, as herbivores may evolve adaptations to overcome these defenses, leading to an ongoing evolutionary arms race.

Review Questions

• How do constitutive defenses compare to induced defenses in plants, and what implications does this have for their survival strategies?
  • Constitutive defenses are always present in plants and provide a continuous level of protection against herbivores and pathogens, whereas induced defenses are activated only after an attack occurs. This difference impacts survival strategies by allowing plants with constitutive defenses to deter threats consistently, reducing their overall vulnerability. However, induced defenses may be more resource-efficient in environments with low herbivore pressure since they allow plants to allocate resources to growth when threats are minimal.
• Discuss the role of secondary metabolites in constitutive defenses and how they affect herbivore behavior.
  • Secondary metabolites play a critical role in constitutive defenses by providing chemical deterrents that can affect herbivore behavior significantly. Compounds such as alkaloids, terpenoids, and flavonoids can make a plant unpalatable or toxic when consumed, influencing herbivores' feeding choices. This not only protects the plant but can also drive herbivores to adapt over time, either developing resistance or changing their dietary preferences.
• Evaluate the ecological significance of constitutive defenses in relation to plant-animal interactions and broader ecosystem dynamics.
  • Constitutive defenses have profound ecological significance as they shape plant-animal interactions within ecosystems. By deterring herbivores through various physical and chemical traits, these defenses help maintain plant populations and influence species composition in communities. Additionally, they play a role in broader ecosystem dynamics by affecting food web structures; for instance, when certain plants are less palatable due to their constitutive defenses, it may lead herbivores to switch their diets or reduce population sizes, subsequently affecting predator dynamics and overall biodiversity.

Related terms

Induced defenses: Defenses that are activated in response to herbivore attack or pathogen invasion, often leading to a quick and localized response to stress.

Secondary metabolites: Chemical compounds produced by plants that are not directly involved in growth or reproduction, often serving ecological functions such as deterring herbivores.

Trophic levels:

The hierarchical levels in an ecosystem, based on feeding relationships, where plants occupy the base as primary producers and herbivores fall into the next level.