A chemical plant produces an insecticide that makes small mammals such as otters infertile. After the factory began operation, the incidence of infertility of an otter living in a nearby river increased rapidly. 
the factory must have polluted the river when producing pesticides.
A low-calcium diet can lead to a decline in poultry egg production. When chickens on a farm are released to look for food in the spring, their egg production is significantly reduced. Therefore, the food they find and eat must be very low in calcium