Northern range shift may be due to increased competition induced by protection of species rather than to climate change alone

Abstract

Few long‐term, large‐scale studies have been conducted about the factors likely to explain changes in species abundance and distribution in winter. Range shifts are generally attributed to the climate change or land use. This study shows that other factors such as species protection and the ensuing increasing numbers of individuals and competition could be involved. It details the progressive conquest of France, the most important European wintering area for great cormorant, in three decades as its legal protection by the EU Birds Directive. It is based on 13 exhaustive national counts. Cormorants first occupied the farthest areas (Atlantic and Mediterranean lagoons, then larger rivers) from the main‐core European breeding area, with only progressive occupancy of the northeastern part later. This strategy mainly resulted from competition for optimal available feeding areas. Suboptimal areas (smaller wetlands harboring smaller night roosts, colder northeastern French areas) and progressive fragmentation of large night roosts into smaller, better located ones minimized flight costs. The coldest areas were occupied last, once other areas were saturated. Their occupancy was favored locally by the global climate change, but it played a minor role in these strategies. Both factors induced only a small NNE shift of the weighted centroid range of the wintering population (2.6 km/year) which mainly resulted from competition (buffer effect). Only the 2009 cold wave decreased the total number of wintering cormorants at the national scale, once the population had probably reached the carrying capacity of the country, while the previous cold waves had a minor effect. Comparatively, there was a greater SSE range shift of the weighted centroid of the breeding population (4.66 km/year). Range shifts of other recently protected species have been attributed to the sole climate change in the literature, but competition due to the saturation of usual wintering or breeding areas should be considered too.

Discriminating climate, land‐cover and random effects on species range dynamics

“…Shifts in geographic distributions of species may also reflect natural population dynamics (Bradshaw et al, 2014), or complex interactions with other factors such as human‐mediated land‐use change (e.g. Guo et al, 2018; Lehikoinen et al, 2013), dispersal limitations (Anderson et al, 2009) competition (Marion & Bergerot, 2018), biological invasions (Sax & Gaines, 2008), disease (Hof et al, 2011) and interactions among several factors (e.g. Vicente et al, 2019).…”

Long-Term Changes in a Pygmy Cormorant Microcarbo pygmaeus Wintering Population in Southern Bulgaria

“…The majority were active in 2001-2004, coinciding with an apparent increase in the national Pygmy Cormorant wintering population (Plachyiski et al 2014), which might explain the formation of several roosting sites simultaneously. Habituation to human disturbance may explain the fragmentation of larger roosts to smaller ones to optimize foraging and energy costs (Marion & Bergerot 2018). Likewise, the human disturbance may cause the abandonment of roosting sites and the consolidation of the Pygmy Cormorants into a single large roost.…”

“…Therefore, changes in wintering conditions are key factors affecting inter-seasonal variation in numbers and distribution of these species and are important to understand (Musil et al 2011, Lehikoinen et al 2016). It is well-documented that wintering distribution of waterbirds shifts to the north-eastwards and positively correlates with changes in temperatures (Lehikoinen et al 2013, Marion & Bergerot 2018, Pavón-Jordán et al 2020). Though climate is crucial (Fox et al 2018), food availability during non-breeding periods, human disturbance and habitat changes are major determinants for the status and distribution of waterbird populations (Maclean et al 2008, Carboneras et al 2013, Volponi 2014, Zou et al 2017, Wang et al 2020).…”

Non-breeding waterbirds benefit from protected areas when adjusting their distribution to climate warming

“…IX.1979) and the Birds Directive (79/409/EEC) in 1979. After that, a fast population recovery occurred notably by a northward expansion (Hiley et al 2013, Ławicki 2014, Marion & Bergerot 2018.…”

“…Despite numerous studies on waterbird distribution changes in response to climate warming (e.g. Maclean et al 2008, Lehikoinen et al 2013, Pavón-Jordán et al 2019, including conservation measures (Johnston et al 2013, Pavón-Jordán et al 2015, Gaget et al 2018, Marion and Bergerot 2018, assessments of differences in waterbird distribution changes at community level inside and outside PAs are still lacking.…”