Mechanisms Underlying the Bioindicator Notion: Spatial Association between Individual Sexual Performance and Community Diversity

Abstract

The bioindicator notion is an appealing concept that has received more support in applied than in basic ecology, mostly due to the difficulty in deriving general ecological rules applicable to all target organisms. However, recognizing the mechanisms that determine the association between a particular species and the well-being of many other species is important for understanding the functioning of ecosystems and the relationship among different biological levels. We examined here the processes at the individual level that cause an association between species performance and biodiversity value, by analyzing attributes that can be studied in a variety of animals with sexual reproduction, namely breeding site selection and condition-dependent sexual signals. Our study model was the Capercaillie, an indicator of forest functioning and diversity, and the associated bird community, used here as a surrogate of broader forest biodiversity. At a regional scale Capercaillie occurrence was not associated with the most diverse forest patches, but at the scale of male spring territories the sexual display grounds (arenas) were located in the oldest and less disturbed forest portions, which also hosted the richest local bird communities. Social mechanisms and conspecific cueing likely concurred with habitat-driven processes in determining the long-term persistence of traditional display grounds, which were appealing to many other species because of their structural composition. Characteristics of male vocal display that honestly advertize male quality (low frequencies and rapid song rates) were significantly correlated with high diversity values, resulting in a spatial association between individual and community performances. Costly or risky activities such as reproductive or social behaviors, which more than other attributes match gradients in habitat quality, are therefore contributing to functionally connect individuals with ecosystem health.

Divergent responses of flagship, keystone and resource‐limited bio‐indicators to forest structure

“…From the whole bird data-set, we extracted density values of cavity nesting birds (8 species, listed in Table 1) in the circular band of 50 m radius only, since these species can be accurately surveyed in 0.78 ha areas (Laiolo et al 2011). The presence/absence of woodpeckers, represented by three species in the study area (Table 1), was estimated in the widest survey band (100 m, surveyed area = 3.14 ha), in order to take into account the largest home range size of these species.…”

“…Because of its special protection in Asturias, spatial requirements and daily routine, the Capercaillie cannot be surveyed by point counts as other bird indicators can. We therefore considered the surveys performed by the Asturian Environmental Agency to obtain data on the presence/absence of this grouse in the study plots in the period 2005 and 2007, plus updated information ob-tained in 2010 (Laiolo et al 2011). Local environmental wardens surveyed 47 sexual display areas (here called leks for simplicity), that were known to be occupied since the 1980s, when the species surveys were first performed.…”

“…in an area of up to 1 km 2 to confirm lek abandonment (Quevedo et al 2006a, b). The same procedure was used by Laiolo et al (2011) to record Capercaillie occurrence and to study its association with bird diversity at increasing distance from the lek center. The entire survey procedure of wardens in the Cantabrian range is described in Quevedo et al (2006a) and Blanco-Fontao et al (2011.…”

“…(2) woodpeckers, specialized cavity-excavating birds that are known to disproportionately impact the community given their abundance (keystone species) (Mikusin´ski et al 2001;Drever et al 2008;Drever and Marin 2010;Remm and Lohmus 2011), and (3) Capercaillie Tetrao urogallus, a flagship species that promotes public support for conservation efforts (Obeso and Ban˜uelos 2003) and which, in specific spatial contexts, becomes an umbrella species associated with high diversity values (Suter et al 2002;Pakkala et al 2003;Laiolo et al 2011) (Table 1). We studied the habitat requirements of the three different indicators, expecting that they will respond differently to different forest structural predictors, given their diverse ecology.…”

“…We studied the habitat requirements of the three different indicators, expecting that they will respond differently to different forest structural predictors, given their diverse ecology. Woodpeckers and cavity nesting birds may be more common in plots with high tree biomass and abundant snags, while the Capercaillie may favor heterogeneous forests (Swenson and Angelstam 1993;Martin et al 2004;S á nchez et al 2007;Laiolo et al 2011). We test whether some indicator (resource-limited, flagship or keystone) is better than others in capturing variation in forest characteristics and can, ultimately, serve to predict ecological changes in forest ecosystems.…”