外來物種
Introduced species are not always disruptive to an environment, however. Tomás Carlo and Jason Gleditch of Penn State University found that the number of "invasive" honeysuckle plants in the area correlated with the number and diversity of the birds in the Happy Valley Region of Pennsylvania, suggesting introduced honeysuckle plants and birds formed a mutually beneficial relationship. Presence of introduced honeysuckle was associated with higher diversity of the bird populations in that area, demonstrating that introduced species are not always detrimental to a given environment and it is completely context dependent.