Holocene extinctions of a top predator—Effects of time, habitat area and habitat subdivision

Abstract

1. Loss of habitat and changes in the spatial configuration of habitats are major drivers of species extinctions, but the responses to these drivers differ between organisms. To advance theory on how extinction risk from different types of habitat alteration relates to species-specific traits, there is a need for studies of the long-term extinction dynamic of individual species.2. The goal of this study was to quantify how habitat area and the spatial configuration of habitats affect extinction rate of an aquatic top predator, the northern pike Esox lucius L.3. We recorded the presence/absence of northern pike in 398 isolated habitat fragments, each one consisting of a number of interconnected lakes. Time since isolation of the habitat fragments, caused by cut-off from the main dispersal source in the Baltic Sea, varied between 0 and 10,000 years. Using survival regression, we analysed how pike population survival was affected by time since isolation, habitat size and habitat subdivision. The approach builds on the assumptions that pike colonized all fragments before isolation and that current absences result from extinctions. We verified these assumptions by testing (a) if pike was present in the region throughout the entire time period when the lakes formed and (b) if pike typically colonize lakes that are formed today. We also addressed the likelihood that unrecorded anthropogenic introductions could bias our estimates of extinction rate. 4. Our results supported the interpretation that current patterns of presence/absence in our study system are shaped by extinctions. Further, we found that time since isolation and fragment area had strong effects on pike population survival.In contrast, spatial habitat subdivision (i.e. if a fragment contained few large lakes or many small lakes) and other environmental covariates describing climate and productivity were unrelated to pike survival. Over all, extinction rate was high in young fragments and decreased sharply with increasing fragment age. 5.Our study demonstrates how the link between extinction rate and habitat size and spatial structure can be quantified. More similar studies may help us find generalizations that can guide management of habitat size and connectivity. K E Y W O R D Saquatic ecosystems, connectivity, extinction, fragmentation, habitat age, habitat area | 1203Journal of Animal Ecology ENGLUND Et aL.

Importance of metapopulation dynamics to explain fish persistence in a river system

“…(2007) showed that for a butterfly species, the total amount of suitable habitat was the best predictor of the probability of metapopulation persistence when compared to the number of patches, the average patch area, and the habitat connectivity. Similarly, Englund et al., (2020) observed that metapopulation size (cumulated area of connected lakes) has been a good predictor of the rate of pike metapopulation extinctions since the end of the Pleistocene. Our study is in line with those observations by showing that the model with metapopulation size (area * Occ, M6) is among the best models and is slightly outcompeted (∆AIC = −0.21) by the very similar one (M7) in which both area and occupancy are entered as predictors.…”

“…Similarly, Englund et al, (2020) observed that metapopulation size (cumulated area of connected lakes) has been a good predictor of the rate of pike metapopulation extinctions since the end of the Pleistocene. Our study is in line with those observations by showing that the model with metapopulation size (area * Occ, M6) is among the best models and is slightly outcompeted (∆AIC = −0.21) by the very similar one (M7) in which both area and occupancy are entered as predictors.…”

Influence of reed beds (Phragmites australis) and submerged vegetation on pike (Esox lucius)

“…Pike in the Baltic Sea, and elsewhere, may migrate to the spawning sites from surrounding areas (Karås and Lehtonen, 1993;Bosworth and Farrell, 2006) so abundance and size may be related to the connectivity between the studied bays and other suitable areas (Englund et al, 2020). Surrounding habitat was not assessed here and in this study we can therefore not infer anything about the importance of surrounding habitat quality or connectivity between habitats.…”

The role of habitat fragmentation in Pleistocene megafauna extinction in Eurasia

“…3, Supporting information). Late Pleistocene Eurasian large mammals had their best survival conditions when several well‐connected habitat patches were available, which allowed maintenance of healthy metapopulation structures (Hanski and Mononen 2011, Englund et al 2020). For now‐extinct species, the degree of connection among patches started to deteriorate noticeably during the 46–36 ka interval (Fig.…”