Final answer:
Yes, populations naive to the toxins produced by Alexandrium would suffer a decreased fitness if they consume a diet containing these toxins.
Step-by-step explanation:
Populations naive to toxic Alexandrium would, yes, indeed suffer a decrease in fitness when fed a toxic diet. The production of toxins, such as those causing paralytic shellfish poisoning, by dinoflagellates like Alexandrium can affect not only marine life but also humans consuming contaminated seafood. Animals that have not evolved specific adaptations to these toxins may face increased predation because they do not possess the defenses required to counteract or survive the toxic effects, leading to a decline in their survival rates and overall fitness.
When evaluating ecosystems and species interactions, it's crucial to consider the balance between predation and defenses. In the case of a dietary intake of toxins by a species within an ecosystem, if the species lacks adaptation to the toxins, it could result in a higher susceptibility to predation since predators may not learn to avoid these organisms. Over time, this could lead to an overall decrease in the abundance of the naive species, impacting the ecosystem's balance.