Winner and loser effects

A theory underlying the causation of the winner and loser effect deals with an animals perception on its own and other members resource holding potential. Essentially, if an animal perceives that it has a high resource holding potential, it considers itself to be a dominant member of an intraspecific community. If an animal perceives that it has a low resource holding potential, it considers itself to be a less dominant member. This perception of resource holding potential is further enhanced or disrupted when aggressive challenges arise. If an animal wins an encounter, its perception of its own resource holding potential increases, just as if an animal loses, its perception of its resource holding potential decreases. Animals, regardless of size, with a higher perception of resource holding potential are more likely to initiate aggressive behaviour to maintain their dominance within a community. Overall, the larger the difference between the perception of two fighting animals resource holding potential, the higher the chance of the animal with the higher resource holding potential of winning the encounter. Based on this theory, an animal who assumes itself as a high resource holding individual is likely to be a dominant/aggressive member while an animal who assumes itself as a low resource holding individual is likely to be a submissive/non-aggressive member of a community. The reason an animal will accept its dominant or submissive position in a hierarchy is because of the game theory model of aggression. Based on the hawk and dove game, being a hawk (aggressive individual) or dove (submissive individual) can be beneficial depending on the fitness associated with the trait. Game theory discusses a frequency-dependent model where both traits (aggressive vs submissive) can exist when the frequency of each meets an evolutionary stable strategy (ESS). == Hormonal stimulation ==

In some animals winner and loser effects have been shown to cause hormonal differences in blood plasma. Research conducted using humans show that after completing a competitive task against another team, the winning team's testosterone goes up, while the losing team's testosterone goes down. It also showed in a group setting that the team member who was the top-scoring player or did the most work received the highest boost in testosterone. == Importance of previous experience ==

Winner and loser effects are driven by an organism's previous experiences, typically in an aggressive context. The most recent fighting experience has the greatest effect on the organism, as testing done on Rivulus marmoratus showed individuals who had lost their most recent encounters (LW) had a higher probability of winning their next encounter than that of a fish who had lost their last encounter but won the one before that (WL). The literature also showed that encounters that happened two times before an aggressive event can affect the strength of the winner or loser effect. This was shown as species who won their last fight, but lost the one before that (LW), had a higher probability of winning their next fight than that of a fish that lost their last encounter but won the interaction before that (WL). == Hierarchy formation ==

'', also known as the Green Swordtail Winner and loser effects also can be attributed to the formation of hierarchies. A study done on Xiphophorus helleri, also known as the green swordtail had shown that individuals who won were more likely to assume alpha or higher ranked positions in a hierarchy, while individuals who lost were more likely to assume omega or lower ranked positions in a hierarchy. Neutral individuals who have little to no experience with aggression interactions fall in an intermediate position between winners and losers forming the winner–neutral–loser (W–N–L) hierarchy. Hierarchies can also be affected by the strength of the winner or loser effects acting upon it. Winner effects alone typically produce linear hierarchies where organism A wins all encounters, organism B wins all encounters except against organism A, organism C loses all encounters except against organism D, and organism D loses all encounters. This linear relationship is typically shown as (A > B > C > D). Loser effects unlike winner effects do not show this linear relationship because animals experiencing loser effects do not fight which makes it difficult to assign a position in a hierarchy. == Examples ==

Loser effects in copperhead snakes '', also known as the Copperhead Snake|250x250px Copperhead snakes rely on aggressive behaviours to fight for a prospective mate. When copperhead snakes are tested to see if winner effects affect their ability to win an encounter it was found that there was no winner effect. In these birds, the nestlings develop one of the following strategies, either dominant or submissive. If first born chicks showed aggression early on towards its siblings, it likely became a dominant member, while if the chick was non-aggressive early on, then it likely adopted the submissive strategy. The study focused on situations where players end up winning or losing the first set by a very small margin (two points at the end of a tie-break lasting more than 20 points). It finds that the winner of the first set has 60% chances of winning the second set, compared to 40% for the loser of the first set. Such an effect is only observed for male players. Another study found that players winning in tennis experience an increase in testosterone level while losers experience a decrease. The famous hot-hand effect in basketball has also been found to exist: players who are successful at scoring during a match increase their likelihood to shoot successfully later on. Winner and loser effects in plants As humans disturb old-growth forests, they are creating more forest edges and gaps. The removal of these trees provide less shading and allow for more sunlight. While the rate of speciation increases in the winners, it is far outpaced by the extinction of the losers. The projected effects of plant loss on biodiversity loss are more significant than any other trophic level. ==See also==