Disentangling the effects of area, energy and habitat heterogeneity on boreal forest bird species richness in protected areas

Abstract

AimOne of the few general laws in ecology is that species richness is a positive function of area. However, it has been proposed that area would merely be a proxy for energy. Additionally, habitat heterogeneity has been found to be an important factor determining species richness. Yet the relative importance of those relationships is little known, and it is still unclear how they are brought about. We aimed to dissect which factors drive the species richness of boreal forest birds, and to identify the most probable mechanisms. Location Forested protected areas in Finland.Methods Using bird line census data collected in 104 protected areas, we ran simultaneous autoregressive models to explain the species richness of forest birds. We explored the value of forest area, tree volume, tree growth, mean degree days and habitat heterogeneity as explanatory variables and used the species richness within different species groups, based on the predictions of hypothesized mechanisms, as a response variable.Results Energy, rather than area or habitat heterogeneity, seems to be the main driver of species richness in boreal forest birds. More specifically, productive energy was a better predictor of total species richness than solar energy. Among the tested hypothetical mechanisms, the sampling hypothesis received strong support. After accounting for sampling, solar energy had an effect on species richness.Main conclusions As productive energy, such as tree volume, is associated with species richness, high-energy areas should be prioritized in forest conservation planning. Reductions in productive energy may first lead to the disappearance of the rarest species due to the random sampling process. Climate change may result in increased species richness due to increasing amount of productive and solar energy in forests. However, the range shifts of bird species may not be fast enough to keep up with the temperature increases.

The Role of Habitat Heterogeneity in Structuring Mangrove Bird Assemblages

“…In structurally simple habitats like mangroves, habitat heterogeneity is less pronounced and may limit the number of coexisting species in mangroves [13]. Many studies have shown that habitats with greater structural complexity support greater bird diversity [14][15][16]. This pattern is not only limited to bird communities but has also been observed in non-volant small mammals [17], ungulates [18], reef fish [19], arthropods [20] and bats [21,22].…”

“…For example, an increase in foliage structural diversity has been reported to increase the number of habitat niches and in turn faunal species richness [5,23,24]. Recently, some authors have suggested that the latter trends arise due to an increase in productivity in complex habitats, which in turn increases the resources available to a larger number of species [16,25,26]. In contrast to these general trends, Cousin and Phillips [15] found no significant correlation between habitat complexity and bird species richness in woodlands of south-western Australia, suggesting that such relationships may be weak in resource poor environments.…”

Coupling high-resolution satellite imagery with ALS-based canopy height model and digital elevation model in object-based boreal forest habitat type classification

“…Furthermore, it has been found that geodiversity and habitat diversity are positively connected (Ja ková and Romportl 2008). Habitat diversity is, on the other hand, positively linked with species richness (Honkanen et al 2010). Therefore, the factors that have an effect on species richness have also interactions.…”

“…That is, the larger the area or the more energy that is available there, the more species there are. Many of the factors that explain species richness can be reduced by means of different mechanisms to energy and area (Honkanen et al 2010). Energy can be understood rather broadly and divided into solar and productive energy.…”

“…Solar energy metrics, such as temperature, quantify the amount of available solar energy. Productive energy metrics, such as net primary productivity, measure the resources available for consumers (Evans et al 2005, Honkanen et al 2010. There are also many other factors used to explain species richness that cannot be reduced to area and energy.…”