Sci-Day 3: Population Ecology

Happy Sci-Day, everyone! Today I'll be covering a topic that will be extremely important for Dinosaur Battlegrounds - namely, the dynamics and ecology of populations.

By 'population', I mean the entire count of individuals of some given species. For example, all Tyrannosaurus rex could be a population. There are a lot of important factors that we need to figure out, that are not necessarily answered just by looking at the fossil record.

Perhaps the most intuitive example is distribution. How large is the natural range for the species? While we can get good estimates for this based on the fossil record and knowledge of potential barriers to migration at the time, it is by no means a complete picture. There may be areas where they existed, but we don't know due to a lack of rocks from that specific place/time, or perhaps the preservation conditions were poor in the region and as such they did not leave fossils. There is also always the simple possibility that there are fossils of that species there, but we simply have not found them yet.

Natural range is not the only aspect of distribution that is incredibly important. There is also the issue of how that population is spread throughout that range. Is it a relatively even distribution, or is it more clumped? This too cannot be completely answered by looking at fossils alone. With animals that live in herds, the population will be more clumped, as there will be multiple herds of many individuals across their range - the opposite is true for a primarily solitary species. If we only have fossils, we don't know if that animal was living alone (and died alone), or if it was part of some group where the rest of the individuals did not die (and thus were not fossilized).

The reason this distribution is important is because it will help us better understand the ecosystem. We may notice that previously unconsidered factors end up affecting distribution - for example, perhaps the presence of nest raiders alters the distribution of dinosaur species, or the density of Tyrannosaurus rex in a given area tends to be no higher than some fixed number.  The latter example relates somewhat to the concept of competition. If there are too many animals trying to make use of a limited resource, there is going to be competition. This competition (and resource availability) limits the population size of any species, along with other factors.

Another key factor of interest is population stability. In Dinosaur Battlegrounds, we need to create a stable ecosystem. In order to do so, we need to figure out how to distribute the many species across the map, and how many of each to put, as well as a general age distribution. If we just do this without any careful thought, it is highly likely that many populations will not be stable, and may go extinct (or drive others to extinction). To help ensure population stability, we have to take at least two variables into account - survival curve/rate and fecundity. Survival curves tell us approximately how the survival rate of that species changes with age, and fecundity tells us how many offspring that species yields in a given breeding. Since this obviously can vary with age (and the value is zero prior to sexual maturity), ecologists may use a projection matrix with the survival rates and fecundity of all 'life stages' (ie 1 year old, 2 year old, etc.), and then multiply that by a matrix with a hypothesized age distribution (ie 100 1 year olds, 75 2 year olds, etc.). The resulting matrix can then be multiplied by the original projection matrix, and this can be repeated as many times as is desired. The results will give an idea as to whether or not the population is stable - if it continues to increase exponentially, that is a problem - it also is a problem if it continues to steadily decrease. However, if it remains at more or less the same total value, you should be good. It will also let you know the hypothetical age distribution of such a population.

Well, I hope this Sci-Day has taught you a little more about population ecology!