The disappearance of algae and elm trees would likely have a significant impact on a food web, but let's analyze each pair to determine the one that would result in the total collapse of the food web.
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Algae and Elm Trees: Algae are primary producers in aquatic ecosystems, while elm trees are primary producers in terrestrial ecosystems. The loss of both would disrupt food sources for multiple trophic levels.
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Algae and Dragonflies: Algae serve as a fundamental food source for many aquatic organisms, but dragonflies are predators and rely on other organisms for food. The absence of dragonflies would affect some populations, but algae's role as a producer is more critical.
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Dragonflies and Foxes: Dragonflies are part of the aquatic food web, and foxes are part of the terrestrial food web. The loss of both would affect their respective ecosystems, but it wouldn't cause an overall collapse.
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Elm Trees and Bass: Elm trees are important for terrestrial ecosystems, while bass are significant to aquatic ecosystems. Their absence would impact their respective food webs, but again, it wouldn't necessarily lead to total collapse.
Given that algae are foundational producers in aquatic food webs, their disappearance would lead to the collapse of aquatic ecosystems. Meanwhile, elm trees are crucial terrestrial producers, affecting herbivores and other organisms that rely on them.
Therefore, the pair whose disappearance would lead most directly to the total collapse of the food web would be algae and elm trees.