Editing Eastern Prickly Pear (section)

=== How can colonies at the coastline become so well-dispersed? ===

If we consider the two questions and answers above, it is clear that ''O. humifusa'' colonizes new habitat areas very, very slowly.  But if we should believe the above assertions to be accurate, then how can a stronghold such as the Long Beach Complex possibly exist?  To summarize, the Long Beach Complex includes literally hundreds of cacti scattered over upon a 1.5-mile stretch of the Long Beach Peninsula.  If ''O. humifusa'' has so aggressively colonized Long Beach, why can't it do the same elsewhere?  The answer to this question rests solely upon a series of beneficial conditions which converge on the Long Beach Peninsula to truly favor the expansion of ''O. humifusa''.

For starters, we have already established that birds are the primary vector for ''O. humifusa'' seed dispersal.  In the case of inland colonies, the species of birds that feed upon pears, as well as the frequency with which the plants are visited, is probably extremely variable.  Coastal areas, however, have served as nesting sites of various seabirds since prehistory.  These coastal nesting sites, which include Long Beach Peninsula, offer unusually high numbers of nesting birds which are tethered to the immediate landscape for several months at a time.  This means that, wherever nesting sites host a population of ''O. humifusa'', the cacti are literally at the dead-center of a dispersal hotspot where pears are routinely foraged by resident seabirds.

Furthermore, unlike inland sites that are typically surrounded by thick woodlands, coastal sites such as Long Beach offer an extremely high ratio of suitable habitat per acre.  Long Beach Peninsula is ripe with wide swaths of open dunes and scrubland, all of which are steeped in direct sunlight and enjoy wintertime low temperatures that are slightly warmer than those experienced at inland locations.  In short, the majority of the landscape on coastal sites tends to be accommodating of the needs of ''O. humifusa'', while a comparatively minute percentage of the inland landscape can provide for the complex needs of the cactus.

Let's consider these more optimal conditions in the same format that we considered them above:

<ol>
<li>
25% of the seeds produced by ''O. humifusa'' aren't eaten in the first place
</li>
<li>
40% of the seeds consumed by birds are dispersed in unsuitable habitat
</li>
<li>
75% of the seeds that are deposited on ideal habitat will not actually germinate
</li>
</ol>

As we can see here, the higher population and longer residence of birds, when coupled with the abundance of suitable cactus habitat, means that the rate of successful short-distance dispersal and germination increases to roughly 11% on coastal sites like Long Beach Peninsula.  While not staggeringly high, this represents a drastic increase over dispersal rates experienced inland.  Thus, the abundance of ''O. humifusa'' on Long Beach Peninsula can be explained as an example of a series of ecological conditions which conspire to help ''O. humifusa'' thrive to a degree that is otherwise unthinkable in most other environments.