Draft:Floaters/Floater Status

Floaters are usually male, but sometimes female, members of a species population that are non-territorial and unpaired for mating, despite being capable of reproducing.. In contrast to floaters, breeders or territory holders will have mates or ownership of any mating resources/spaces. As opposed to just “non-breeding secondaries” in a population, floaters are specifically non-territory holding and/or do not tend to remain in a certain territory like “breeders” and “non-breeding secondaries.” Floaters usually differ in some way from breeders in age, condition, or morphology. Floater status is a new concept in the biological world, thought to be caused by size, condition, or testosterone level. Due to differences in ornamental trait expression and size, territorial trait exclusion could be a cause or a consequence. Floaters in populations, despite not reproducing, may be important for population regulation, as well as the long-term persistence of a population. Floaters can contribute to population stability and regulation by acting as reserve mates, prohibiting changes in population size by rapidly replacing breeders if needed. Similarly, floaters can act as reserves of genetic diversity within a population. They can also be warning indicators of population decline, as shifts in floater traits can be indicative of breeder mortality rates. Many juvenile members of a population may count as floaters because they have not yet obtained the condition or experience needed to mate. In cases where juvenile floaters end up mating later in life, they are considered more as a developmental stage rather than a fraction of the population. Floater status can beoften caused by uneven sex ratios in a population, through limited mating options, or mating space. They often appear in polygamous mating systems or in high-density populations wherein specific mating criteria, like nesting, is harder to obtain. Floater duration is another aspect of floater status that is still being studied, since in short-lived species, a single mating season may result in zero lifetime reproductive success for a floater [5].

Floater hypotheses

There are five current theories/hypotheses examining what qualifies a population member as a floater and why floaters exist. These theories are not mutually exclusive, and were primarily developed by studying a population of migratory kites (Milvus migrans)

1: Resource-holding Potential Hypothesis:

In this hypothesis, breeders are in some way morphologically superior to floaters. For example, a difference in size or coloring that is less attractive to possible mates.

2: Age Hypothesis:

This hypothesis states that age drives skills and competitive motivation and therefore younger members of a population are more likely to be floaters. This seems to be more of a general rule, however, through which floater status is revoked once the juvenile floater comes of age and establishes social or territorial dominance.

3: Site-dominance Hypothesis:

This hypothesis describes how time spent and, therefore, familiarity in a population site could cause a floater to not claim territory. These aspects also affect a floater’s perceived mating value. This then means that newness among a population and a location can drive floater status.

4: Arbitrary Convention Hypothesis:

This hypothesis details how competitors within a population establish an arbitrary rule to resolve contests/competition, meaning that certain meaningful biological traits (like age and size) leave floaters at a disadvantage and develop an established cut-off between breeders/territory-holders and floaters in the population.

5: Arbitrary Attrition Hypothesis:

This is where floaters set up a “war of attrition” with certain territories in which they will work together to reduce the fitness of a group of individuals and isolate them from a section of territory to better their own chances of survival and therefore reproduction.

Results of Recent Testing:

Floating status was most prominently explained through a combination of the age and site-dominance theories when tested among migratory black kites (Milvus migrans). These results suggested that, among this population, age and length of time in a territory established territorial dominance and distinguished breeders from floaters.

Identification

Floater identification is a relatively new endeavor. Identification of the floaters in a population has proven to be difficult due to their often secretive behavior in populations. Another difficulty in identifying floaters is that it is much harder to track territory holders in populations that migrate. Floaters are most often found in migratory bird populations, like the black kite (Milvus migrans), the New Zealand hihi (Notiomystis cincta), and gulls (Larus argentatus) in which female floaters were observed. The most common method of identification is through the removal of territory holders and the monitoring of how quickly that territory is claimed by non-territory holders. As floaters are most often found among bird species, one option for the identification process is to mark and identify an entire population to understand the proportion of floaters within a population, although that is a difficult and lengthy task. Floaters are often tracked through wing-tagging or telemetry. Non-invasive genetic testing techniques have been developed through the testing of feces and molted feathers in order to estimate floater abundance in a population. For example, the testing of collected feathers was used to investigate the population of floaters of Eastern imperial eagles in Kazakhstan. An estimation of the floater population was made by comparing the microsatellite genetic profiles of shed feathers of assumed floaters to the profiles of the chicks hatched after the breeding season in order to test if the owners of the feathers breed successfully. Floater percentage can also be estimated by working backward from the rate of mate and territory replacement after the loss of a mating pair [5].

Males

Large amounts of male floaters in a population may drive competition through territorial behaviors and mate guarding among the territory holders (non-floaters) and, in response, will cause extra-pair copulation and increased territorial tactics among floaters. Males, as the most observed floaters, often resort to aggressive extra-pair copulation when exiting non-breeder status but remaining in non-territorial status.

Females

Female floaters, in attempts to gain breeding opportunities, will contribute to female-female aggression and signaling of dominance over other females. There are also theories that selection has driven quality signifying traits among these females in order to be more attractive to their potential mates. One major example of female floaters in a population is among European herring gulls in which non-breeding females spend significantly more time attempting to seduce male population members than breeding females. They also defend territories just as much as paired members of their population, assisting the overall reproduction in their population without contributing to it themselves.

Floaters in relation to endangered species

Though floaters are generally non-breeders, some still breed through extra-pair (non-monogamous) copulation. This means that floaters can still affect the sex ratio for the rest of the breeding population. This is especially significant among endangered species and small populations wherein floaters can greatly affect sex ratio, inbreeding, and most importantly, reproductive variance which can then affect the rate of genetic drift and reduce genetic diversity. In endangered species, like the New Zealand hihi (Notiomystis cincta) for example, where the proportion of floaters is large floaters can act as population stabilizers.