Re: On predation.

chris brochu (
30 Oct 1995 00:11:59 GMT

In article <> H. M. Hubey, writes:
>>And incorrect. Check population statistics for alligators in North
>>America. They breed at a high enough rate that they will spread quickly.
>that's not the point. See my other post on croc infestation
>in SAudi Arabia.

As it happens, there were crocs in the Saudi peninsula during the
Pliocene; perhaps during the Pleistocene as well.

>>Sorry, but this has happened.
>OK. Now let me reverse the tables. Give me documented
>evidence for a croc traveling over 20 miles of land. :-)..

Very well.

Several authors describe the fact that adult crocs don't like making long
land treks, but that they will do so if required. A coffee-table book
entitled "Crocodiles and Alligators" (ed. C. A.Ross, Facts on File,
1989, p. 96) shows a nile croc that was overtaken by a grass fire on
land. (While you have this book, check out the PHOTO on p. 52 of a
crocodile ON A BEACH ;-).

As for the primary literature, there are numerous accounts of crocs on
land. The best - and most relevant, since we're discussing Africa - is
Hugh Cott's monograph on C. niloticus in Uganda - a work that should be
on the bookself of any African ecologist. He agrees that crocs prefer
not to make long land travels, but he states (p. 231):

"In northern Rhodesia Major W.E. Poles came upon a seven-foot crocodile
in the middle of an open plain about a mile and a half from the nearest
lagoon. More remarkable is the instance reported by Trollope to Player,
from the Chobe River, where he met a crocodile travelling across country
*fifteen miles* from the nearest water."

Cott gives citations for the above, and discusses survivability of crocs
in dry conditions.

(Full reference:
Cott, H.B., 1961. Scientific results of an inquiry into the ecology and
economic status of the Nile Crocodile (Crocodilus niloticus) in Uganda
and Northern Rhodesia. Trans.. Zool. Soc. Lond., 29(4):212-352.)

Sorry - I couldn't find a reference for 20 miles. But will 15 do?

In any event, the distance crocs will walk is utterly irrelevant. Let me
use a highway analogy - suppose you are driving on a highway that forks.
Instead of taking the right fork, you bear left and head off in the wrong
direction. According to Hubey, the only solution is to drive your
vehicle off the highway until you get to the correct path. Crocs are
unwilling, but perfectly capable, of doing this; more likely, they will
turn around and take the correct path at the junction.

>>The big deal is this - you contend that aquatic predators will not spread
>>if bodies of water are far enough apart. You do not know that this was
>It's simple logic that it's easier to travel on land for predators
>and on water for aquatic ones. Lions can't swim across 100 miles
>of sea and crocs can't walk across 100 miles of savanna.
>[use the sentences are statistical generalities.]

Perhaps. But, as above, is there any reason to believe that this is the
only way for crocs to spread?

Crocs have a number of things in their favor when it comes to
repopulating. Compare, for example, the success of alligator restocking
with the relative failure we've had keeping the Florida panther around.
Panthers breed more slowly and require larger territories. Alligators
breed very quickly - something that compensates for their unwillingness
to travel on land - and aren't as territorial. As a consequence, 'gators
periodically show up in swimming pools. I doubt many of these pools are
connected to major drainages.

The most important point is this - the rapid spread of alligators and
saltwater crocs with protection virtually falsifies any thought that they
cannot spread quickly.