Coevolution refers to the process where two or more species reciprocally influence each other's evolution due to mutual interactions. Often, competition can be a driving force behind coevolution. When species compete for resources, they can undergo evolutionary changes to exploit different resources (niche differentiation), alter their behaviour, or adapt their physiology. If these changes subsequently affect another species, prompting it to also evolve in response, a coevolutionary dynamic is established. For instance, a plant might evolve tougher leaves to deter herbivores, which in turn might evolve stronger jaws or digestive enzymes to process the tougher leaves, and so on.

Temporal separation, or time-based separation, is a strategy organisms use to avoid direct competition. This occurs when different species utilise the same resource but at different times. By avoiding simultaneous resource use, they reduce direct competition and the potential depletion of that resource. An illustrative example is nocturnal versus diurnal species in a shared habitat. While both might rely on similar food sources, one species feeds during the day, and the other feeds at night. This separation in time reduces competition and allows both species to coexist without exerting intense evolutionary pressures on each other. Natural selection may have favoured these time-based behaviours to promote coexistence and resource optimisation.

Keystone species play a crucial role in maintaining the structure, diversity, and functionality of an ecosystem. Their presence or absence has a disproportionately large impact relative to their abundance. For instance, a keystone predator might keep the population of a particular herbivore in check. Without this predator, the herbivore population might explode, leading to overgrazing and intensified competition among herbivores for food. This could drive natural selection, favouring herbivores that can exploit alternative food sources. Alternatively, without the keystone species, some species may outcompete others, leading to a reduction in biodiversity. Thus, keystone species indirectly shape the paths of natural selection in their ecosystems.

An ecological niche is the role an organism plays in its ecosystem, encompassing its use of resources and its interactions with other organisms. When two species have overlapping niches, they often compete for the same resources, leading to interspecific competition. If the competition is intense, it may force one or both species to evolve different strategies or behaviours to reduce overlap. This process is known as niche differentiation or resource partitioning. By minimising direct competition, species can coexist more harmoniously in shared habitats. The adaptations or changes that arise due to niche differentiation are a direct outcome of natural selection, working to optimise each species' chances of survival and reproduction.

Carrying capacity refers to the maximum number of individuals of a particular species that a given environment can support sustainably over the long term, considering available resources. When a population exceeds this capacity, competition for resources intensifies. As resources become scarcer, only those organisms with advantageous traits (adaptations) can obtain sufficient resources to survive and reproduce. This selective pressure enforces natural selection, promoting the proliferation of advantageous traits within the population. Over time, populations stabilise around the carrying capacity, but if environmental conditions change, the carrying capacity can shift, leading to further evolutionary pressures and adaptations.