Habitat fragmentation and reproductive success: a structural equation modelling approach

Abstract

Summary1. There is great interest on the effects of habitat fragmentation, whereby habitat is lost and the spatial configuration of remaining habitat patches is altered, on individual breeding performance. However, we still lack consensus of how this important process affects reproductive success, and whether its effects are mainly due to reduced fecundity or nestling survival. 2. The main reason for this may be the way that habitat fragmentation has been previously modelled. Studies have treated habitat loss and altered spatial configuration as two independent processes instead of as one hierarchical and interdependent process, and therefore have not been able to consider the relative direct and indirect effects of habitat loss and altered spatial configuration. 3. We investigated how habitat (i.e. old forest) fragmentation, caused by intense forest harvesting at the territory and landscape scales, is associated with the number of fledged offspring of an area-sensitive passerine, the Eurasian treecreeper (Certhia familiaris). We used structural equation modelling (SEM) to examine the complex hierarchical associations between habitat loss and altered spatial configuration on the number of fledged offspring, by controlling for individual condition and weather conditions during incubation. 4. Against generally held expectations, treecreeper reproductive success did not show a significant association with habitat fragmentation measured at the territory scale. Instead, our analyses suggested that an increasing amount of habitat at the landscape scale caused a significant increase in nest predation rates, leading to reduced reproductive success. This effect operated directly on nest predation rates, instead of acting indirectly through altered spatial configuration. 5. Because habitat amount and configuration are inherently strongly collinear, particularly when multiple scales are considered, our study demonstrates the usefulness of a SEM approach for hierarchical partitioning of habitat amount vs. habitat configuration in landscape ecology that may have bearing on biological conclusions.

Using change trajectories to study the impacts of multi-annual habitat loss on fledgling production in an old forest specialist bird

“…17 showed clear area-sensitivity in the occupancy of treecreeper nest box sites, but the wood volume used in that study was over 150 m 3 /ha, which was higher than the level used in this study (100 m 3 /ha). However, several previous studies have shown that the same habitat definition used in this study can affect both physiological and life history traits in treecreepers 18–20 . Second, errors in the classification of satellite images might have resulted in false change in the results, for example showing decreases in habitat cover in sites that had stable habitat cover.…”

“…We summed the number of fledged offspring per nest box site over the entire study period, which enabled us to quantify the cumulative impacts of continuing habitat change on species that could have been easily missed when using static snapshots of habitat data. We used percent cover of forest over 50 years in age as an estimate of habitat amount since it has previously been shown to be associated with territory occupancy 17 and nestling body condition of treecreepers 18 at the territory core scale, and nest predation 19, 20 at the landscape scale. Importantly, we also investigated whether the level of initial habitat cover moderated the influence of change in habitat cover on treecreeper fledging numbers.…”

“…Based on our previous results on this system 17, 20 , we hypothesised that: (1) decreasing habitat cover at the territory core scale would decrease the number of fledged offspring by reducing the total number of nesting events, (2) decreasing habitat cover at the landscape scale would increase the number of fledged offspring because of lower predation pressure, and (3) a high level of initial habitat cover in the nesting site would protect the sites against the negative influence of decreasing habitat cover.…”

Nestling diet optimization and condition in relation to prey attributes and breeding patch size in a patch-resident insectivorous passerine: an optimal continuum and habitat constraints

“…Habitat fragmentation can adversely affect the reproductive success of birds primarily through reducing pairing success, lowering the survival of adults through nest predation and parasitism, and reducing the availability of critical resources such as food (Le Tortorec et al 2013). In particular, small habitat patches may supply little food owing to their being completely isolated or of inferior quality.…”

“…This may adversely affect reproductive success, since habitat patch size limits territory size and hence food availability. Even if the territory size in poor habitats could be enlarged, this would come at a cost because of the longer foraging distances required (reviewed in Le Tortorec et al 2013). Therefore, the size of the breeding patch can influence the nutritional status of growing nestlings because adults feeding altricial young will be constrained in their foraging by the location of the nest (Hinsley et al 1999;Zanette et al 2000).…”