Ecological traps in isodars: effects of tallgrass prairie management on bird nest success

Abstract

2005. Ecological traps in isodars: effects of tallgrass prairie management on bird nest success. Á/ Oikos 111: 159 Á/169.Ecological traps occur when habitat selection and habitat suitability (measured in terms of fitness) are decoupled. We developed a graphical model based on isodar theory to distinguish between an ideal distribution and an ecological trap. We tested the model's predictions using data on breeding bird populations in managed tallgrass prairie in Oklahoma. Between 1992 and 1996 we monitored success for 2600 nests of 26 breeding species in undisturbed, grazed, and burned and grazed plots. We also sampled arthropod biomass and nest predator abundance. Using the isodar model we determined that managed plots are ecological traps: compared with success on plots left undisturbed, nest success on plots that were only grazed was lower, and success on plots that were burned and grazed was substantially lower. Yet birds preferred to nest on managed plots, where arthropod abundance was measurably higher. Reptiles were the most abundant taxon of nest predators, and their abundance was highest in managed plots. Consequently, tree-nesting species had higher nest success than shrub-and ground-nesting birds. Nest success also increased with tree height. We concluded that isodar theory is a useful tool for detecting ecological traps if any component of fitness is measured in addition to animal densities. Our study also suggests that (1) human modification of the environment may alter simultaneously food and predator abundance, (2) the former affects nest site selection and the latter nest success, and (3) such ecosystems are likely to become traps for breeding birds.

Nest survival of Woodpigeons (Columba palumbus) in North African forests

“…A similar pattern has been reported in studies of nesting success in many bird species (Winter & Faaborg 1999, Conway & Martin 2000, Shochat et al 2005. The pattern may be because in this part of the Middle Atlas, food resources become increasingly scarce at the end of the breeding season (MPEP 2006) so that the adults may spend more time searching for food and chicks may die from starvation.…”

A biodiversity-friendly rotational grazing system enhancing flower-visiting insect assemblages while maintaining animal and grassland productivity

“…to complete their life cycle (Dennis et al, 1997). Moreover, the effect of the BR system on insect assemblages should also be examined at the end of the growing season, as D subplots may turn into an 'ecological trap' (Shochat et al 2005) when re-grazed after the exclusion period. Indeed, although the subplots which were not grazed during the main flowering period did attract adult insects, their eggs and larvae or nests might later have suffered from livestock disturbances in August.…”

Assessing the Habitat Suitability of Two Different Artificial Wetland Habitats Using Avian Community Structures

“…It was also found that adjacent dry land area dominated by patches of shrubs and fruiting trees had also attracted a number of bird species particularly upland birds i.e., may be only facultative marsh inhabitants (Knight et al, 2001). It has been reported that birds often select habitats that offer specific foraging and nesting sites (Shochat et al, 2005;Kloskowski et al, 2010;Mcnew et al, 2012).…”

“…Furthermore, the results clearly indicated that habitat selection of bird species may vary from species to species, depending upon avian behaviours such as foraging, nesting, loafing and roosting. Finally, many non habitat-related phenomena also influence the habitat selection in birds such as nest predation (Shochat et al, 2005;Marzluff et al, 2007), competition for foraging and nesting (Sherry, 2006), intraspecific attraction (Forsman et al, 2002;Rajchard, 2007;Sridhar et al, 2009) and food limitation (Musil, 2006).…”