Not only does the relationship that Darwin observed help the species survive, but it also causes them to evolve in order to achieve a more seamless relationship with each other, and thus a better probability of survival. The two species will evolve through natural selection to better fit each other’s niche. If a flower has a very deep nectary, insects that have long proboscises will be able to reach the nectar of the flower and survive, while insects with short proboscises will die. Meanwhile, flowers that have certain traits that makes it easier for the insects to feed, while still maintaining a successful system of attaching pollen to the insect will be able to reproduce more efficiently and thus pass on their traits and evolve its own species. The stimulus of the insects on the flower and the stimulus of the flower on the insects to evolve and change their physical traits is coevolution.
One example of coevolution is the relationship the Bullhorn Acacia, a swollen-thorn acacia native to Mexico and Central America, has with colonies of Stinging Ants that occupy the hollowed-out thorns of the plant. The ants fiercely defend the tree against ravaging insects, browsing mammals and epiphytic vines and in return, the Bullhorn Acacia supplies the Stinging Ants with protein-lipid Beltian bodies from its leaflet tips and carbohydrate-rich nectar from glands on its leaf stalk. (In this example, both the Bullhorn Acacia and the Stinging ants benefit from each other. The co-evolutionary relationship that the acacia and the ants share is called a mutual relationship where both species benefit.)
Here it can be seen that the Bullhorn Acacia has evolved in a way that supplies the Stinging Ants with food. It can be assumed that Bullhorn Acacias that could produce protein-lipid Beltian and nectar more efficiently were more capable at surviving because of the Ants that occupied the Acacia for the protein and nectar. At the same time, the Stinging Ants can survive because of the sustenance they attain from the Acacia.
Another example of coevolution can be seen in the relationship between the Australian Hammer Orchid and the Thynnid Wasp in Australia. During mating season, the female Thynnid wasp will emerge from living underground and travel to a high position and position itself in a way where it releases pheromones that attract a male wasp. The male wasp will find the female through its shape and scent. The male wasp attaches itself to the female and lifts it into the air and then proceeds to engage in sexual reproduction.
However, during the same time the Hammer Orchid blooms. The pedals of the Orchid assume and mimic the shape, and even release the same scent, as the female wasp. This replication of the female wasp’s characteristics deceives the male wasp into attaching itself to the pedal of the Orchid. When the male wasp attempts to fly away with the pedal, it is guided by the stem of the Orchid to a sticky deposit of pollen that affixes to the hairy area of the wasp’s back. Once the wasp realizes that it cannot pull the “female wasp” off, it yields and flies away with the pollen deposit on its back. However, the wasp is only to be lured again by another orchid performing the same deception tactic. In the process, the wasp transfers pollen from flower to flower. (In this example, the relationship is only beneficial to the Orchid, while wasp receives no benefits. This type of co-evolutionary relationship is called a commensal relationship where one organism benefits but the other does not). It can be seen that the Hammer Orchid evolved in a way in which it took advantage of the mating rituals of the Thynnid Wasps and thus was capable of surviving.
In conclusion, the relationship between two species of organisms can have a drastic impact on the way they develop and spread. The symbiotic relationship that two organisms share change and alter them in a way that helps them survive and flourish. Those organisms that do not possess the necessary traits that help them survive die out while the ones with the beneficial traits survive. At the same time, the organisms that survive influence and stimulate the change of the organisms that depend on them and, in turn, influence the evolution of the dependent organism. Coevolution can be beneficial to both parties of organisms or beneficial to only one party of organism. However, the influence that the organisms share with each other indirectly changes stimulates the evolution of the species.