Editing Grouse (section)

==Sexual size dimorphism==
=== Male size selection ===
The phenotypic difference between males and females is called [[sexual dimorphism]].<ref name=ssd /> Male grouse tend to be larger than female grouse,<ref name=ssd /> which seems to hold true across all the species of grouse, with some difference within each species in terms of how drastic the size difference is.<ref name=ssd /> The hypothesis with the most supporting evidence for the evolution of sexual dimorphism in grouse is sexual selection.<ref name=ssd /> Sexual selection favors large males; stronger selection for larger size in males leads to greater size dimorphism.<ref name=ssd /> Female size will increase correspondingly as male size increases, and this is due to heredity (but not to the extent of the male size).<ref name=ssd /> This is because females that are smaller will still be able to reproduce without a substantial disadvantage, but this is not the case with males.<ref name=ssd /> The largest among the male grouse (commonly dubbed 'Biggrouse') attract the greatest numbers of females during their mating seasons.{{citation needed|date=October 2020}}

=== Mating behavior selection ===
{{Main|Lek mating}}

Male grouse display [[Lek mating|lekking]] behavior, which is when many males come together in one area and put on displays to attract females.<ref name=Fiske>{{cite journal |last1=Fiske |first1=Peder| last2=Rintamaki |first2=Pekka |last3=Karvonen |first3=Eevi|title=Mating success in lekking males: a meta-analysis |journal=Behavioral Ecology |date=1998 |volume=9 |issue=4 |pages=328–338 |doi=10.1093/beheco/9.4.328 |doi-access=free}}</ref> Females selectively choose among the males present for traits they find more appealing.<ref name="Fiske"/> Male grouse exhibit two types: typical lekking and exploded lekking.<ref name=ssd /> In typical lekking, males display in small areas defending a limited territory, and in exploded lekking, displaying males are covered over an expansive land area and share larger territories.<ref name=ssd /> Male grouse can also compete with one another for access to female grouse through territoriality, in which a male defends a territory which has resources that females need, like food and nest sites.<ref name=ssd /> These differences in male behavior in mating systems account for the evolution of body size in grouse.<ref name=ssd /> Males of territorial species were smaller than those of exploded lekking species, and males of typical lekking species were the largest overall.<ref name=ssd /> The male birds that exhibit lekking behavior, and have to compete with other males for females to choose them, have greater sexual dimorphism in size.<ref name=Soulsbury>{{cite journal|last1=Soulsbury|first1=Carl D|last2=Kervinen|first2=Matti|last3=Lebigre|first3=Christophe|title=Sexual size dimorphism and the strength of sexual selection in mammals and birds|journal=Evolutionary Ecology Research|date=2014|volume=16|pages=63–76}}</ref> This suggests the hypothesis of sexual selection affecting male body size and also gives an explanation for why some species of grouse have a more drastic difference between male and female body size than others.{{citation needed|date=October 2020}}

=== Contrast with other bird species ===
Sexual size dimorphism can manifest itself differently between grouse and other birds. In some cases, the female is dominant over the male in breeding behavior, which can result in females that are larger than the males.<ref name="ReferenceA">{{cite journal| last1= Mueller |first1= H. C.|title= The Evolution of Reversed Sexual Dimorphism in Owls: An Empirical Analysis of Possible Selective Factors |journal= [[The Wilson Bulletin]] |volume=98|issue=3|pages=387–406}}</ref>