Caves were just an example, and pretty much the rest of your comment actually proves my point. If a "more active predator" enters a cave and subsequently eats e

Caves were just an example, and pretty much the rest of your comment actually proves my point. If a "more active predator" enters a cave and subsequently eats everything and dies, then evolution has selected against it. Evolution selects species that best fit the environment, and that generally means species that find a sustainable balance through both internal and external regulation mechanisms. Your example doesn't require an invasive species. Aggressive species (ones with their consumption and reproduction clocks set "too high") can arise through mutation, too. In either case they spread like cancer and usually take down parts of the ecosystem with them before they are finally selected against. Eventually, ecosystems find mechanisms to limit the damage of cancer-like species and adjust everyone's "clocks" to appropriate levels. Ecosystems that cannot bring their species into stasis experience repeated shocks, are less stable than ones that do find stasis, and often disappear. This is exactly why the long arc of evolution is best understood as a punctuated equilibrium (https://en.wikipedia.org/wiki/Punctuated_equilibrium https://en.wikipedia.org/wiki/Punctuated_equilibrium) rather than a constant drift. Systems that find stasis are more successful than ones that don't. Unfortunately these systems are repeatedly interrupted by drastic environmental changes like geological events. So, the systems that survive are the ones that tend toward balance but are able to adapt to occasional disruptive events. That requires biodiversity that is generally reduced by aggressive species. > To visualize this, watch one of those speeded-up videos of starfish and sea urchins. At our pace, they are sedentary. At their pace, it's Thunderdome all day every day. Or look at hardwood forests that develop extremely slowly over thousands of years, despite the availability of plenty of energy from the sun. The slower the system, the better it actually proves my point. Clearly, evolution does not select for the fastest growing, most aggressive species out there. Otherwise starfish and sea urchins would move faster, or be displaced by something that moved faster. Properly understood, ecosystems are super organisms that require many many moving parts to bootstrap, grow and function. Human bodies are analogous. Your cells aren't trying to "outcompete" every other cell in a Thunderdome situation every day. They are carefully regulated both internally and externally. When those regulatory mechanisms fail, you end up with cancer and you die. Clearly, cell replication rate is a key regulator internal to a cell that prevents us all from experiencing runaway cancer and dying. Clearly ecosystems have species with internal regulation mechanisms as well.