What limits where an organism is found? This seemingly simple question has been a frequent topic of conservation as we explore the lakes around Kangerlussuaq. Some lakes contain an astonishingly high amount of sea tomatoes (we estimate thousands of large colonies in some lakes) while we couldn’t locate a single sea tomato in others (despite hours of searching). We are currently exploring three general models to explain this pattern, which are illustrated below using fish as an example.
1) Dispersal Limitation
It is possible that this fish could exist in the both lakes, but that it is unable to travel from one lake to another. Such barriers to dispersal could be natural features of the landscape or ones created by humans.
2) Abiotic Constraints
It is also possible that the physical environment in the right lake does not enable the fish living in the left lake to survive and reproduce. Some common abiotic constraints for life include temperature, salinity, and pH.
3) Biotic Pressures
It is also possible that the physical environment is suitable for the fish in both lakes, but that the lake on the right contains a larger piscivorous, or fish-eating, fish that would cause the other fish to go extinct. Besides predation, other biotic pressures that can limit the range of a species include the presence (or absence) or parasites, pathogens, or mutualists.
We hope that our observations allow us to determine which of the above models best explains the patchiness of sea tomatoes in lakes around Kangerlussuaq.