Population control of an overabundant species achieved through consecutive anthropogenic perturbations

Abstract

Abstract. The control of overabundant vertebrates is often problematic. Much work has focused on population-level responses and overabundance due to anthropogenic subsidies. However, far less work has been directed at investigating responses following the removal of subsidies. We investigate the consequences of two consecutive perturbations, the closure of a landfill and an inadvertent poisoning event, on the trophic ecology (d 13 C, d 15 N, and d 34 S), survival, and population size of an overabundant generalist seabird species, the Yellow-legged Gull (Larus michahellis). We expected that the landfill closure would cause a strong dietary shift and the inadvertent poisoning a decrease in gull population size. As a long-lived species, we also anticipated adult survival to be buffered against the decrease in food availability but not against the inadvertent poisoning event. Stable isotope analysis confirmed the dietary shift towards marine resources after the disappearance of the landfill. Although the survival model was inconclusive, it did suggest that the perturbations had a negative effect on survival, which was followed by a recovery back to average values. Food limitation likely triggered dispersal to other populations, while poisoning may have increased mortality; these two processes were likely responsible for the large fall in population size that occurred after the two consecutive perturbations. Life-history theory suggests that perturbations may encourage species to halt existing breeding investment in order to ensure future survival. However, under strong perturbation pulses the resilience threshold might be surpassed and changes in population density can arise. Consecutive perturbations may effectively manage overabundant species.

Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes

“…As a consequence, abundant research has been conducted on these opportunistic predators, mainly focused on their population dynamics, feeding ecology, pollution levels and pathogen load (e.g. Ramos et al 2011, Payo-Payo et al 2015. However, most of these studies consider conspecifics as ecological equivalents.…”

“…However, most of these studies consider conspecifics as ecological equivalents. Although this simplification can be useful to provide an overview of population-level feeding preferences or population dynamics (Ramos et al 2011, Payo-Payo et al 2015, taking into account the individual component within populations is essential for a better understanding of the main ecological mechanisms related to the success of winning species (Grémillet et al 1999, Cardador et al 2012, Chapple et al 2012, Liebl & Martin 2014, Ceia & Ramos 2015, Potier et al 2015 Individual specialization occurs when some individuals within a population utilize only a subset of the resources that the population uses as a whole. This may be expressed via an animal's diet, patterns of movement or other specific behaviour (Bolnick et al 2003, Matich et al 2011, Ceia & Ramos 2015.…”

“…This species is a clear example of a winning predator in southern Europe, as a result of its ability to efficiently exploit a diverse suite of novel resources (e.g. Alonso et al 2015, Payo-Payo et al 2015, Martínez-Abraín & Jiménez 2016. This gull is also considered a pest within urban, agricultural and coastal areas (Vidal et al 1998).…”

Predator–prey dynamics of bald eagles and glaucous‐winged gulls at Protection Island, Washington, USA

“…Gulls are scavengers and gull populations increased dramatically during most of the twentieth century (Amlaner et al, ; Duhem, Roche, Vidal, & Tatoni, ; Kadlec & Drury, ; Sullivan et al, ). Closure of landfills in this and other regions worldwide has been associated with sharply reduced gull populations (Payo‐Payo et al, ). Indeed, the 1992 closure of the Coupeville Landfill (Anonymous, ), a popular feeding site for gulls located 19 km northeast of the Violet Point gull colony (Schmidt, ), was followed by a 10‐year decline in gull nest counts on Violet Point (Figure ).…”

Reducing agricultural loss and food waste: how will nature fare?

“…Landfills constitute important food sources for a large number of bird species worldwide, particularly for opportunistic and scavenging species (Pomeroy, 1975;Belant, 1997). An increase in landfill sites has been implicated in the growth of a number of gull populations in both the northern and southern hemisphere (Spaans & Blokpoel, 1991;Payo-Payo et al, 2015). For example, the western gull Larus occidentalis populations in western North America has increased significantly over recent years, primarily because of food supplementation from landfill (Osterback et al, 2015).…”