+over grazing
+over hunting
+deforestation etc.
It would be difficult to determine the "biggest" threat to kiwi. Major threats are introduced animals such as dogs, cats and stoats. However, were it not for habitat loss, these animals would not be such a major threat.
Homo Sapiens, or humans.
Rivers, animals, Indians, and disease.
Jellyfish are eaten by squid. I believe that this is the biggest threat that they face.
the market economy was the single biggest threat
Churchill thought that Hitler was the biggest threat in WW2
Biggest threat is a landowner with a 22 rifle or 12ga shotgun.
you are
Polar bears are hunted by people, and circumstantially by orca. The biggest threat to them is global warming.
a lion.
Itself
The greatest threats to numbats are foxes and feral cats. Since the introduction of these animals, the population of the numbat has suffered considerably. Prior to this, the biggest threat were native birds of prey.