Experimental evidence for an ideal free distribution in a breeding population of a territorial songbird

Abstract

Abstract. According to the ideal despotic distribution (IDD), dominant individuals gain a fitness advantage by acquiring territories that are of higher quality, thereby forcing other individuals into lower quality habitat. In contrast, the ideal free distribution (IFD) predicts that local density is a function of habitat quality, but that individuals achieve the same fitness in different habitat types as a result of density-dependent variation in territory size. Although the IFD represents an alternative, population dynamics of territorial species are generally expected to be driven by an IDD. We tested the predictions of IFD and IDD by monitoring the demographic response of the Ovenbird (Seiurus aurocapilla) to selection harvesting (30-40% tree removal) during the first five years postharvest in five pairs of 25-ha study plots, each comprising a control (undisturbed) and a treatment (harvested plot). In the first year following harvesting, Ovenbird territory size increased in treatment plots relative to controls, whereas density, productivity per unit area, and the abundance of litter invertebrates decreased. Treatment effects declined consistently as stands regenerated, and most effects were no longer significant by the fifth year postharvest. However, there was no treatment effect on daily nest survival rate nor on per capita productivity. These results are consistent with the IFD, whereby similar per capita productivity is achieved across habitat types through density adjustments facilitated by changes in territory size. To our knowledge, this is the first study providing evidence for an IFD in a territorial bird species.

Forestry and conspecifics influence Canada Warbler (Cardellina canadensis) habitat use and reproductive activity in boreal Alberta, Canada

“…Setting aside areas with high densities is assumed to have the greatest long-term potential to stop the decline of species that are limited by the amount of breeding habitat remaining. High density areas also tend to have the highest per unit area reproductive output (Skagen and Yackel Adams 2010; Haché et al 2013). Thus, identifying areas with high density and producing the greatest among of young, is key to defining critical habitat.…”

Numerical Response of Breeding Birds Following Experimental Selection Harvesting in Northern Hardwood Forests

“…In addition, there was no evidence for local extinction or a dramatic decline in mature forest associates. In the same study plots, Haché et al (2013) found no effect of selection harvesting on per capita productivity and daily nest survival rate of Ovenbirds, suggesting that individuals can nest successfully in selection cut stands (see also Leblanc et al 2011) by increasing the size of their territories to account for lower food abundance. There is also growing evidence that early-seral stands can be important for mature forest associates during the postfledging period (Vitz andRodewald 2006, Chandler et al 2012).…”

Tree lizard (Urosaurus ornatus) growth decreases with population density, but increases with habitat quality

“…The Ideal Free Distribution assumes individuals are free to choose any habitat, have perfect knowledge of habitat suitability and of the distribution of competitors, and are equal competitors (Fretwell & Lucas, ). Despite its unrealistic assumptions (Kennedy & Gray, ), the Ideal Free Distribution and its extensions have been useful for predicting the spatial distribution of organisms between habitats (Haché & Bayne, ; Milinski, ; Walhström & Kjellander, ). Another central assumption of habitat selection models, however, is that populations experience density dependence (Clutton‐Brock, Major, Albon, & Guinness, ; Morris, ; Skogland, ).…”