Answer:The short film Some Animals Are More Equal than Others: Trophic Cascades and Keystone Species opens by asking
two fundamental questions in ecology: “What determines how many species live in a given place? Or how large
can each population grow?” The film then describes the pioneering experiments by Robert Paine and James Estes,
in the 1960s and 1970s, which started to address them. Paine’s experiments on the coast of Washington state
showed that the starfish is a keystone species, having a disproportionately large impact on its ecosystem relative
to its abundance. Estes and colleague John Palmisano discovered that the kelp forests of the North Pacific are
indirectly regulated by sea otters, which feed on sea urchins that consume kelp. The presence or absence of sea
otters causes a cascade of direct and indirect effects down the food chain, which in turn affect the structure of
the ecosystem. These early experiments inspired countless others on keystone species and trophic cascades in
ecosystems throughout the world.
Explanation:
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