It is possible for many native and alien species to coexist, given the tendency for competition to exclude native species?
- Do we necessarily have to look to different trophic levels to evaluate impacts of a plankton invader?
In ddition to what Dr. Andrew Paul McKenzie Pegman has stated, I would like to add that "the impact of alien species" is only a concern when the supposed alien species has established itself it its new habitat to the point where it is proliferating successfully. It should be noted that most of the accidental or ignorant (may also be intentional) introdcution of exotic species hardly leave a lasting impression on the ecosystem as often they just simply fail to sustain themselves over a considerable time period. Once they do however, their potential to become invasive depends entirely on their ability to either exploit niches and resources at a more energetically economic way so that the resources, otherwise limited at certain time of the year to the natives do not necessarily become so for the exotics, or in their aggressive ousting of the natives owing to the greater physical/temperamental attributes. In both cases the outcome is the dominance of the introduced ones in conjunction with the marginalization/decline of many of the native species.
To answer your question in a concise manner I would say - NO, we do not necessarily have to monitor various trophic levels SOLELY to evaluate the impact of invasive species as invasion can occur in a transient manner gradually over a period where surveys perfomed at one given temporal point may not necessarily reveal the shift effectively and efficiently. As with any other field in ecology, a well thought of and inclusive multivariate study is needed to ascertain the changes being brought about by any introduced and subsequently successful planktonic species.
Hope this helps.
Regards.
Dr. Abhishek Mukherjee
One should consider Environmental limiting factor along with resources.
Dr. Vinaya Tari
thank you so much for this. may I ask you another question? If three invasive species within the same environment fluctuate in population density terms, driven by the same set of abiotic variables, do I have an indication of invasional meltdown?
Could be. But invasional meltdown cannot be established on three random non-indigenous species unless you have a sure enough proof of their introduction within a very narrow time frame to the environment. If not then it could simply be a case of few of the later species coping with the new environment while the earlier introduced and hence more settled spcies are proliferating under the same physicochemical set up. Invasional meltdown is described as the compoundment of then dominance of one introduced and invasive species by another more recent introduction but it many a times ignores the ecological struggles which the species endure, whether dominant or not. Once you have a proof of the co-introduction or simulataneous invasion as well as a time series study to support the actual decline of one by the other then you can definitely make statements about possible invasional meltdown scenarios.
With regards,
Dr. Abhishek Mukherjee
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