Diversity and Disturbances in the Antarctic Megabenthos: Feasible versus Theoretical Disturbance Ranges
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The intermediate disturbance hypothesis (IDH) predicts a hump-shaped relationship between regional diversity and the disturbance rate. We tested the IDH for the megabenthos inhabiting the Antarctic sea floor, which is disturbed by iceberg scouring. We used models based on the empirical knowledge of succession to calculate the IDH curve for this system and to extrapolate the presently observable range of the IDH curve to higher and lower disturbance rates. Although the hump-shaped relationship has been found for a purely theoretical (extremely large) disturbance range, within the feasible disturbance range (assumed as realistic in the Antarctic region under climate change), the regional diversity of successional stages due to iceberg scouring strongly decreases with lower disturbance rates but levels off only slowly with higher disturbance rates. The reason is the unevenness in the lifetimes of the successional stages, in that early stages are short-lived whereas late stages are long-lived. With such unevenness, increasing disturbances support the early stages without jeopardizing the later ones. Additionally, we converted this regional diversity of stages to the regional diversity of taxa using a transformation formula based on empirical knowledge of the number and mean abundance of taxa in the particular stages. Our results suggest that a decrease in iceberg scouring due to climate change would be more detrimental to the diversity of the Antarctic megabenthos than an increase.