Spatial Dynamics of Alternative Reproductive Strategies: The Role of Neighbors

Abstract

In territorial species, the reproductive success of a male is dependent on the quality of his territory. One important component of territory quality is spatial location. High‐quality territories not only should be located in areas of high food abundance and low predation, but also should be located in areas that offer optimal amounts of social interaction. Such optima might be different for individuals according to their sex, dominance, or genotype. We studied territory quality (size, vegetation structure, and placement) in a socially monogamous, polymorphic passerine, the White‐throated Sparrow (Zonotrichia albicollis), in order to determine how spatial attributes contribute to selection intensity on two genotypes. In this species, plumage (white and tan), behavior, and life‐history characteristics have a genetic basis and are correlated with the presence or absence of a chromosomal inversion. Using remote sensing and Geographic Information Systems (GIS), we found that the territories of white and tan males do not differ in size or vegetation structure, suggesting that these factors are not of primary importance to males when deciding where to establish a territory. Instead, we suggest that the placement of white and tan territories depends on the number of neighbors (particularly, white male neighbors). Tan males settle in low‐density, neighbor‐restrictive habitats where intruder pressure from white males seeking extra‐pair copulations is reduced. In contrast, white males tend to settle in high‐density areas where the probability of encountering neighboring fertile females is greatest. This segregation has led to intraspecific niche partitioning in the two disassortative pair types so that each male morph can best exploit its respective reproductive strategies. These factors may, in turn, contribute to the maintenance of this unusual mating system and, ultimately, the stability of the polymorphism in this species. Similar forces may be operating in other species without distinct morphological markers; we suggest that researchers keep social factors in mind when examining habitat selection.

Research Needs and Recommendations for the Use of Conspecific-Attraction Methods in the Conservation of Migratory Songbirds

“…For instance, there is evidence that conspecific attraction of the Least Flycatcher (Empidonax minimus) could be driven by a hidden-lek strategy (Wagner et al 1996, Tarof et al 2005, Fletcher 2007). However, not all individuals may benefit from increased paternity by settling close to conspecifics, and some males (e.g., subdominant males) might benefit from avoiding settling close to dominant males (Greene et al 2000, Formica et al 2004.…”

Short- and long-term consequences of individual and territory quality in a long-lived bird

“…In particular, quality estimates can aVect Wtness in Wve ways, which can be considered as working hypotheses: (b1) territory quality is the only determinant of Wtness (Alatalo et al 1986;Warner 1987;Pärt 2001;Przybylo et al 2001); (b2) individual quality is the only determinant of Wtness (Simmons 1988;Horn et al 1993;Carrete et al 2006); (b3) both individual and territory quality independently aVect Wtness (Hill 1988;Bart and Earnst 1999); (b4) individual and territory quality aVect Wtness but their eVect is interactive (Lõh-mus and Vali 2004); and (b5) Wtness is related to neither individual nor territory quality (Leonard and Picman 1988;Formica et al 2004). …”

New insights into the hormonal and behavioural correlates of polymorphism in white-throated sparrows, Zonotrichia albicollis

“…Behavioural studies over the next two decades demonstrated that TS and WS birds often differ in territorial aggression, parenting behaviour and mating strategy (Collins & Houtman, 1999; Formica & Tuttle, 2009; Knapton & Falls, 1984; Kopachena & Falls, 1993a, 1993a, b; Tuttle, 1993, 2003), which led to a consensus in the current literature that morphs show alternative reproductive strategies (Formica et al, 2004; Formica & Tuttle, 2009; Maney, 2008; Tuttle, 2003). Multiple authors have since described a number of endocrine differences between the morphs (Lake et al, 2008; Maney, 2008; Horton & Holberton, 2009, 2010; Spinney et al, 2006; Swett & Breuner, 2008, 2009), suggesting that morph-typic strategies may be hormone mediated.…”