Every organism in an ecosystem relies on other species for survival: Species diversity. An ecosystem is a biological community of interacting organisms and their physical environment. The survival of one species therefore depends on the survival of other species.
Reduced options for mates can lead to inbreeding: Genetic diversity. Inbreeding occurs when closely related individuals breed, and this can lead to the expression of undesirable traits such as those associated with recessive genes.
Decreased diversity can lead to increased susceptibility to disease: Genetic diversity. This is related to inbreeding. The expression of recessive genes can decrease the overall fitness of a species and increase its susceptibility to disease.
The loss of a producer could result in the loss of consumers: Species diversity. This is related to the concept of an ecosystem. Consumers rely on producers as a food source.
When a population becomes small, diversity is lost: Genetic diversity. This is commonly known as the 'founder effect'.