The workload can be tough and competition is fierce. There are many who can do the job better and for lower wages. This is why you'll have to bring your 'A' game to every job duty every day. Yes, you can be replaced and the others employed at the same facility know that they can as well. There is a pattern to one up the last persons’ comment or presentation. The rule of the unwritten playbook is to do better than what comes before in order to score more points with the boss and peers. In this way there is no chance that you'll lose your job to a replacement that has less experience.
Competition at work is measured by the output created by each employee. Mike's report is better than Stan's while Karen's presentational skills are far more superior to Marcia's. Either way you look at the situation all contenders have strong points and, hopefully, they're learning from each other through the nature of the sport. Productivity is the outcome of this friendly game, but sometimes it does little to stir greater output.
The time spent working on a daily basis can range from the usual eight hours to a far longer period like twelve or even sixteen hours. This depends on the nature and magnitude of the assignment requested. In this and in all other tasks you must appease your boss and participate in the expected extra hours so that you'll remain part of the team for now and company later.
Forces affecting retention are many. It's a good plan to have all bases covered and be prepared to bat the team in at any given time. Your role is critical and to remain employed, as you've learned, it takes a strategy. This routine entails being first and right in decisions and advice. Fortunately for you, these are the things at which you excel. The proven track record comes down to your expertise and the boss is sold on your qualification which is why you've survived the competition to date.