Answer:
the biggest change to San Joaquin Valley ecosystems caused by humans in the past 150 years is the shortage of water in the river.
Step-by-step explanation:
During 150 years, the San Joaquin Valley ecosystems was extremely damaged by the human activities such as building of dams and diversion of river. The San Joaquin Valley has a productive agriculture land due to availability of water. Due to building of dams, the amount of water in the river is decreases and also the population of many fish species decreases. this is because of the disturbance occurs in their natural habitat due to human activities.