Question

Based on the study of \(\mathrm{O}_{2}\) needs and stores, the aerobic dive limit (ADL) for young Weddell seals weighing \(140 \mathrm{~kg}\) is calculated to be \(10 \mathrm{~min}\), whereas that for fully grown \(400-\mathrm{kg}\) Weddell seals is calculated to be about 20 min. Why might small individuals in general be expected to have shorter ADLs than large individuals? To carry out an empirical study of the changes in ADL during postnatal development in a species, what experiments and measurements would you plan?

Short answer

Smaller individuals generally have shorter ADLs due to their higher metabolic rates and smaller oxygen stores. To study changes in ADL during postnatal development in a species, one would need to measure dive durations, weight, size and physiological parameters of the animals. The study might require both field tracking and laboratory testing.

Step-by-step solution

Comprehending Aerobic Dive Limit

Aerobic Dive Limit (ADL) is the duration for which an animal can dive while maintaining aerobic metabolism, meaning oxygen consumption matches the oxygen stores without resorting to anaerobic metabolism. Larger individuals have larger oxygen stores (due to larger size and mass) which allow them to maintain aerobic metabolism for longer duration, hence the larger ADLs observed.

Explaining ADL in Smaller Individuals

Smaller individuals, like young seals, have less body mass and thus smaller oxygen stores. They require comparatively more oxygen per kilogram of body weight than larger animals due to higher metabolic rates. This results in faster depletion of oxygen stores, leading to quicker initiation of anaerobic metabolism and hence shorter ADLs.

Planning Empirical Study

In order to empirically study the changes in ADL during postnatal development, one would need to measure the duration of dives (to determine ADL), the weight and size of the animals (to correlate with ADL), and potentially physiological parameters (heart rate, blood oxygen levels, etc). Both laboratory and field studies may be required. In field studies, one could track the animals using GPS or monitor dive durations directly. Laboratory studies might involve examining tissue samples or carrying out metabolic tests to ascertain oxygen consumption rates.

Key concepts

Oxygen Stores

Oxygen stores refer to the reserves of oxygen available in an animal's body for supporting its metabolic needs during a dive. These stores are located throughout the body in various forms, including in the lungs, blood, and muscles.
- In the lungs, oxygen is held in the air sacs and is one of the first sources used during a dive. - The blood's oxygen reserve is carried by hemoglobin, and it provides a significant portion of the dive oxygen. - Muscles store oxygen in myoglobin, which serves as a reserve specifically for muscle activity during dives.
Larger animals, like fully grown Weddell seals, have larger bodies that can hold more of these oxygen stores compared to their younger, smaller counterparts. This increased capacity allows them to maintain aerobic metabolism longer, contributing to longer aerobic dive limits (ADL). Understanding how these stores are utilized and replenished is crucial for comprehending animal diving behaviors.

Anaerobic Metabolism

Anaerobic metabolism is the process by which animals metabolize energy without using oxygen. This process kicks in once the oxygen stores are depleted.
- It is less efficient than aerobic metabolism, yielding less energy from food molecules. - It produces lactic acid as a byproduct, which can accumulate and lead to fatigue.
For diving animals like seals, prolonging aerobic metabolism is preferred because it provides a steady and efficient energy supply without accumulating lactic acid. Shorter aerobic dive limits in smaller or younger seals mean they rely on anaerobic metabolism sooner, leading to quicker fatigue and the need to surface more frequently for air. Managing their energy use effectively is vital for survival and foraging success underwater.

Metabolic Rate

Metabolic rate is the energy expenditure of an organism, which can vary based on size, age, and activity level.
- Small or young animals typically have higher metabolic rates compared to larger animals. - Higher metabolic rates mean a faster consumption of stored oxygen, reducing the time they can maintain aerobic metabolism during dives.
This explains why smaller seals have a shorter aerobic dive limit. The increased energy demands necessitate more frequent breathing, limiting the duration they can stay underwater using aerobic processes. Understanding metabolic rate differences among age and size can provide insights into the lifestyle and diving capabilities of aquatic animals.

Postnatal Development

Postnatal development encompasses the growth and maturity changes an organism undergoes after birth. For aquatic species like seals, postnatal development affects how their bodies manage oxygen and energy during dives.
- As seals develop, their body mass and oxygen stores increase significantly, enhancing their capacity for longer dives. - This development also involves the maturation of diving reflexes and improved locomotive abilities which aid in efficient energy use.
Studying postnatal changes can reveal shifts in aerobic dive limits and help researchers understand how young seals adapt to their marine environments. Field and laboratory studies could measure these changes, observing the progression from reliance on shorter, more frequent dives to longer, sustainable ones as their bodies mature.

Physiological Parameters

Physiological parameters include various measurable aspects of an organism's bodily function, important in understanding diving capabilities.
- Key parameters include heart rate, blood oxygen levels, and breathing patterns. - Changes in these parameters during a dive indicate how seals manage oxygen stores and metabolic processes.
By monitoring these physiological signals, researchers can gain insights into the efficiency and limits of aerobic metabolism. Advanced methods might include attaching devices to monitor heart rates or blood oxygen online during real dives. Such data help refine models of diving behavior, contributing to a better understanding of how physiological traits support survival and efficiency in the aquatic lifestyle.