evolutionary pressure tingling

i sit for the past few months, now, in a new office that looks out through a tall, contiguous class pane. i suppose that these architectural window-walls, or whatever the proper term may be, are all the rage in this era of office-buildings (though, the floor plan is one of those open-plan designs, which are quickly falling out of favour). In any case, right beside my desk is a floor-to-ceiling glass window, divided by some support beams at about an arm's length. On the outside of these support beams are some protruding beams, which i also assume are for support, but i have no idea what they're called.

Skipping the poorly-described structure of this outlook from my window, here is the point: when i first started sitting here, the window was quite spotless, but over the past few months, it seems that these support beams have provided an opportunistic (and somewhat interesting) dwellings for, at first one spider, but now a whole host of them. i did not realise that spiders could and would live in such close proximity to each other, and as the web grew in size, i just assumed that this was the cumulative effort a single (and somewhat singular) spider in expanding its web - the spider would expand upon the previous web when i was not watching, but would then hide in the crevice between the support beam and the window when i was around.

however, when an insect would inevitably become trapped in the web, the spider would quickly dash out to secure its meal (which always made for an interesting observation, regardless of how busy i was at work), and since the web is right in my field of vision as i face this computer, it is very apparent when this happens - thence, i've noticed that there was not one spider, but multiple of them who come out to claim their prey!

now, to the interesting bit. i've also noticed that the spiders vary in sizes, perhaps even in species or so, as they shape differently - i cannot tell for sure, as i am no entomologist. generally, only one spider would run to an entrapped insect (i can only assume this is proximity-based, as spiders 'hear' their prey through the vibrations in the webs, so the closest spider would hear first the insect in distress?). every once in a while, though, two spiders might skitter towards the same insect, where the larger spider would claim the prey and the smaller one would have usually backed off before getting to it (i await the day a smaller spider actually challenges a larger one. does this happen? is it an issue of dominance, or is this unnecessary in the superfluousness of food supply?).

as per my earlier assumption, i believe spiders were generally solitary insects, except during a mating incidence, however, these spiders have clearly formed a community of sorts, where they've all benefited from the web array being larger than that of an individual's, though i wonder at what point competition will begin to apply more survival pressure than the said conferred benefit? perhaps this has already occurred, but i have yet to notice it.

interestingly, in a corner of the window, which is a bit more hidden from my view, is a large, single web with a single spider inhabitant, which has no other spider. has he chased off potential neighbours, warranting and giving no quarter to potential competitors? has he chosen a poorer spot to ensnare unwitting insects? or is he merely the leader of the world's tiniest anti-social social club? we may never know. spider, tell me your secrets.

attached a photo of the web in the corner that is in my visual range, though it doesn't do the web much justice.