Natural enemies boost deep evolutionary fitness?

Question

"Two species that reduce one another's fitness on microevolutionary (short-term) timescales can increase each other's macroevolutionary (long-term) fitness"

Opinions?

Intuitive Examples:

• Body Size - Predator-prey relationships or interference relationships (fighting, e.g. for territory) are often documented to put seletion pressures to grow in body size, often a positive feedback loop. In the short term the presence of the natural enemy in this case often leads to decreased population fitness (probability of being eaten/probability of fatal conflict over territory). But in the long term such large body sizes acts as an advantage over potential future enemies of the same kind. This is particularly relevant to marine ecosystems - where the size of fish often determine where in the food chain that fish is.

• Speed/agility - Predators and prey that rely on speed/agility to
  capture (predator) or escape (prey) undergo an evolutionary arms race leading to positive feedback of speed/agility boosting morphologies. In the short-term the natural enemy of the prey acts as a burden to
  population fitness (probability of being eaten) but in deep time the prey has acquired morphological advantages over potential future
  natural enemies such as competitors for resources.

• Venomousness -Why do venomous animals live in warm climates?

Answer 1

The question is interesting.

I am afraid about the use of the word "fitness" in you question. The fitness is usually defined as the number of offsprings an individual can sire in its lifetime. Most often we talk about relative fitness which is the relative number of offspring in an individual can sire in its lifetime compare to the individual in the population that sire the greatest number of offsprings.

How would you compare fitness of individuals between different species? Just by counting the number of offspring they left behind? Or did you mean that most fit species are actually those species that can outcompete others? If yes, then I would say that saying

Two species that reduce one another's fitness on microevolutionary (short-term) timescales can increase each other's macroevolutionary (long-term) fitness

can be restated

Two species that reduce one another's fitness on microevolutionary (short-term) timescales can increase each other's macroevolutionary (long-term) species competition ability

and it is actually just a special case of

One species that evolve under many strong selection pressure ends up being a very competing species.

The explanation is the following:

One species that undergoes one selective pressure, will see its genetic variance decreases. The weak individuals will disappear letting places to the strong individuals. Then newly arisen variance (mutation) will come up only in the strong individuals (as the other ones disapeared). This is what J.Gould meant by saying "Natural selection creates the fit". As a consequence a species that undergo many successive selection pressure will end up with purified and very strong genotypes while, in a species that were free to evolve without selection they would have evolved many different genomes with some good mutations nested in very poor genetic background.

You could as well use the concept of lineage selection and states that lineage that succeeds to outcompete others will thrive while species that suffer from competition with other species will get extinct. As a result, if you compare all species that were in competition with another species in the past with all species that were not in competition, you will find out that those that were in competition are more resistant to competition. But I guess this is not exactly what you meant when saying: "Two species that reduce one another's fitness on microevolutionary (short-term) timescales can increase each other's macroevolutionary (long-term) fitness"

Finally you might think of the ability of species to evolve better. This ability is called "evolvability" (see this book for example). You might say that species that undergo many selection pressures were selected to resist to newly arisen selection pressure. As a result, species that are under competition might end up with a greater evolvability than those that were not under selection. Resulting that species that were under competition will tend to increase to always increase their fitness in the long term.