第47回生態適応セミナー (Aセミナー)

     
  日時 9月24日(金曜日)10:30‐  
  場所 生物地学共通講義室(青葉山キャンパス)  
     

講師:
Dr. Peter Bellingham (Landcare Research, New Zealand)

     
  Seabirds, predators, and how they affect island ecosystems  
     
 

Seabirds are an important component of coastal ecosystems throughout the world because they transport marine nutrients into terrestrial environments and they create a specific disturbance regime. Seabird predators have disrupted seabird-driven ecosystems worldwide, and some predators, such as rats, have reached remote island ecosystems relatively recently. I present results of studies conducted on warm temperate New Zealand islands, some never invaded by predators and with large seabird colonies, and others invaded by ship rats or Norway rats within the last 150 years, where seabirds have either been eradicated or reduced to very low numbers. Plant composition and plant community structure differ between the two island groups. Disturbance by burrowing seabirds results in greatly reduced seedling regeneration, but which species regenerate is also likely to be mediated by nutrient supply. There is evidence that rat invasion results in nitrogen limitation because litter nitrogen concentrations are lower on islands invaded by rats, and the litter of some plants releases much less nitrogen. Invasion of islands by rats results in c. 40% more total carbon on islands, with a strong shift from belowground to aboveground carbon storage. Reduction of seabirds by predators results in major decreases of most groups of soil organisms, and the abundance of many soil organisms is strongly linked to seabird abundance. Eradicating seabird predators has been achieved on many islands within the last two decades. There is some evidence that plant seedling densities become more like those on uninvaded islands within 15 years of rat eradication. Establishing new seabird populations on islands, through translocation of chicks, may be needed to achieve island restoration.