Here's the explanation:
1. Surface Area to Volume Ratio:
- Smaller animals have a larger surface area relative to their volume compared to larger animals.
- This means they lose heat more rapidly due to their high surface area.
- To compensate for this heat loss and maintain body temperature, smaller animals need to generate more heat, which requires a faster metabolism.
2. Metabolic Rate:
- The metabolic rate is the rate at which an organism converts food into energy.
- Smaller animals have a higher metabolic rate compared to larger animals because their bodies need to work harder to maintain the same level of activity.
- This increased metabolic rate requires a faster heartbeat to deliver oxygen and nutrients to the cells more rapidly.
3. Heart Rate and Oxygen Delivery:
- A faster heartbeat ensures that oxygen-rich blood is pumped throughout the body more quickly, meeting the higher oxygen demands of smaller animals' cells and tissues.
4. Evolutionary Adaptation:
- Over time, smaller animals have evolved to have faster heartbeats as an adaptation to their smaller size and higher metabolic needs.
- This adaptation has allowed them to maintain proper body temperature and sustain their higher energy requirements.
5. Relationship with Body Mass:
- In general, there is an inverse relationship between body mass and heart rate among different animal species.
- Smaller animals, with their lower body mass, tend to have faster heartbeats, while larger animals have slower heartbeats.
6. Exceptions:
- While smaller animals generally have faster heartbeats, there are exceptions to this rule.
- Some larger animals, such as elephants, have relatively slow heart rates, while some smaller animals, such as hummingbirds, have exceptionally high heart rates.
In summary, smaller animals have faster heartbeats due to their higher metabolic rates and the need to maintain body temperature. This adaptation ensures efficient oxygen delivery to cells and supports their overall physiological functions.