This is interesting, and you are correct that my speculations lack any solid empirical grounds and depends more on a lack of data to justify. Thus good skeptical rebuttals as you have provided are of particularly high value. This issue of bio-distribution and invasion is particularly problematic. Certainly the limiting factors must be significant. The rosyside dace this thread is based on is particularly problematic.
A large variety of factors would influence the potential for storm transport, aside from the regional and directional storm characteristics. An attempt to list these would include:
1) Species habits lending to the potential for getting caught in storm debris.
2) Initial population sizes, larger species population are more likely to have some individuals caught in storm debris.
3) The need for enough members of a species to establish a breeding colony in a contingent environment.
4) The life spans of species that increase/decrease the probability of transport of breeding pairs in contingent environment.
5) Species capacity to survive the transport in storm debris.
6) Species capacity to survive the environments the debris might fall in.
7) The propensity for subspecies previously transported and subsequently diverged to reabsorb newly transported specimens.
Unlike bait bucket and intentional introductions, these storm transports would be of very low intensity. This allows local populations to usually deal with, reabsorb, or out compete these storm introductions even in cases where breeding populations were potentially possible. Something that cannot be done when bait bucket or intentional introductions involve high numbers of instantly available breeding populations. So to make any case on the available data looking at a few individual species cases would be useful. Any other species cases fitting this profile for likely storm transport would be appreciated, especially clear cases of exceptions.
The two I will consider here is the green sunfish (Lepomis cyanellus), which first showed up in our duck pond, and the Alligator Gar (Atractosteus spatula). The green sunfish for obvious reasons of personal observations and the Alligator Gar due to high survivability in a range of conditions, including breathing air, high lifespan, 60 to 70 years giving the potential for waiting dozens of years for a breeding partner, and low geographic distribution contrary to expectations of an indiscriminate distribution mechanism.Lepomis cyanellus:
For the green sunfish consider the following source:http://maps.gis.iast...s/IA168132.html
These fish are essentially ubiquitous throughout the US. What is said of the the state of Iowa here essentially applies everywhere.
The green sunfish is undoubtedly one of the most widely distributed fish in Iowa and is the most wide-ranging sunfish species (Harlan et al. 1987). It is found in every watershed in the state. This ubiquitous fish is found in streams of all sizes but reaches its greatest abundance in natural lakes, man-made lakes and farm ponds (Harlan et al. 1987). The green sunfish inhabits the full length of the Mississippi River, and is prevalent in the prime habitat created by the riprap armoring placed along the banks of the Missouri River (Harlan et al. 1987).
Even more interesting is the "Habitat Affinities".
The green sunfish can be found in a wide variety of habitats ranging from small muddy creeks and weedy backwaters with temporary flow to overflow ponds, shallow lakes, impoundments and occasionally, the margins of large rivers of low gradient (Becker 1983; Cross and Collins 1995; Eddy and Underhill 1974; Phillips et. al. 1982; Trautman 1981). The green sunfish is commonly found near shore and around cover such as stems of vegetation, woody debris, or rocks (Cross and Collins 1995), and has no specific substrate preference (Robison and Buchanan 1988; Trautman 1981). Its high tolerance for extremes in turbidity, siltation, low oxygen, temperature and flow allow it to inhabit, and reach greatest abundance, in areas that do not support other sunfishes (Clay 1975; Pflieger 1997; Robison and Buchanan 1988). In the Central Plains Aquatic Subregion, the green sunfish is well adapted for survival in small streams with intermittent flow that become stagnant pools later in the summer and fall. A pioneering species, it is often the first fish to find it way to newly created farm ponds (Smith 1979) and first to repopulate Plains streams after droughts (Pflieger 1997; Tomelleri and Eberle 1990).
They apparently specialize in surviving adverse conditions and being the first to populate new environments. For the life of me, even if this species survived dry periods in the creak flood regions to the west and came within the vicinity of the duck pond, I cannot imagine how they would cross the embankment into the duck pond. It was several years before the pond, after some heavy rains, filled sufficiently to produce an overflow channel. Even then the drain channel was initiated by rain directly impacting the embankment, lowering it, to eventually have a channel low enough to produce an overflow. It remained a large puddle in the bottom of a hole for a long time.
So here we have a species with huge numbers over a huge geographic, greatly increasing the likelihood of becoming part of storm debris, while specializing in surviving the very conditions needed to survive storm transport. Not many species would have the numbers, range, survivability, surface interaction, etc., to mimic these numbers over even a reasonable slice of geologic time. If breeding colonies fail over the short term then no amount of geologic time will effectively provide breeding colonies.Atractosteus spatula:
This species has a very long lifespan with a high survivability in highly adverse environmental conditions. Though larger specimens are presumably far less likely to be storm transported this species can effectively wait dozens of years for an effective breeding partner. So the question is why would there historic range be so limited, and can storm transport play any role in the historic range they did have?
The following range map was taken from:http://wildedtx.blog...rve-better.html
Green - Naturally Sustaining Populations
Orange - Remnant Populations or Individual Observations
Red - Stocked Population
Yellow - Approximate Historic Range (Possible Extirpated)
Here it is obvious that throughout the range 'swimming there' could easily be the primary mechanism of transport. But why is the the historic distribution to the northeast so extensive while failing to 'swim to' far closer available habitats in any other direction? In fact many easily available habitats far more similar than the northeastern extent are orders of magnitude closer and easier to 'swim to' which they did not even successfully cross the state in the northwesterly direction. Meanwhile they historically crossed many more mile to the northeast. The Mississippi River plays a significant role here but look at another map:http://www.sdafs.org.../AGar_Maps.html
Note how the northwesterly splits in Arkansas and Missouri are significantly limited in spite of plenty of river access to continue, while the northeasterly track continues unabated. Notice also that these northwesterly splits remain in a northeasterly line with preexisting populations to the southwest. So mere river transport and access (swimming there) does not fully account for this progression of historic range. In fact it more closely follows historic storm transport routes. Otherwise there is no real explanation of why they would fail to progress up one leg of a river while progressing up the other northeasterly leg unabated. This historic distribution matches almost precisely how the winds off the Gulf move inland and are caught by easterly winds from the rockies and bent in an easterly direction. It is this confluence of warm Gulf moisture, easterly winds, and northern cold fronts that produce these historic storm tracks. Over geologic time this historic storm track likely also help produce the general drainage patterns seen today. Also, it is fairly obvious that the ancient populations originated in coastal regions, all the way down the eastern coast of central America.
At least in principle it appears to follow the hypothesis. Any counterexamples to these cases? Coastal regions east of Louisiana are far more limited in storm penetration from the Gulf, except where it crosses over Florida. The Smoky Mountains form a natural push line diverting weather systems in an arc over the region. Hence the Etowah River drainage system in Georgia is effectively isolated from these storm transports with a resulting isolation and subsequent high degree of biodiversity relative to other regions. Another reason why the Etowah Watershed is imperiled by exotic incursions introduced by people. So this storm transport model also correctly predicts biologically isolated regions.
This model is little more than suppositions which may be misleading. Yet on the data we have it cannot be empirically rejected. Even if misleading it still remains to be explained why its general characteristics apparently have some level of explanatory power.
I truly do appreciate your capable rebuttals. Any (counter)-examples?