The sensitivity of breeding songbirds to changes in seasonal timing is linked to population change but cannot be directly attributed to the effects of trophic asynchrony on productivity

Abstract

A consequence of climate change has been an advance in the timing of seasonal events. Differences in the rate of advance between trophic levels may result in predators becoming mismatched with prey availability, reducing fitness and potentially driving population declines. Such "trophic asynchrony" is hypothesized to have contributed to recent population declines of long-distance migratory birds in particular. Using spatially extensive survey data from 1983 to 2010 to estimate variation in spring phenology from 280 plant and insect species and the egg-laying phenology of 21 British songbird species, we explored the effects of trophic asynchrony on avian population trends and potential underlying demographic mechanisms. Species which advanced their laying dates least over the last three decades, and were therefore at greatest risk of asynchrony, exhibited the most negative population trends. We expressed asynchrony as the annual variation in bird phenology relative to spring phenology, and related asynchrony to annual avian productivity. In warmer springs, birds were more asynchronous, but productivity was only marginally reduced; long-distance migrants, short-distance migrants and resident bird species all exhibited effects of similar magnitude. Long-term population, but not productivity, declines were greatest among those species whose annual productivity was most greatly reduced by asynchrony. This suggests that population change is not mechanistically driven by the negative effects of asynchrony on productivity. The apparent effects of asynchrony on population trends are therefore either more likely to be strongly expressed via other demographic pathways, or alternatively, are a surrogate for species' sensitivity to other environmental pressures which are the ultimate cause of decline.

Phenological responses in a sycamore–aphid–parasitoid system and consequences for aphid population dynamics: A 20 year case study

“…Climate‐induced changes in synchrony between the phenology of insects and that of their resources and natural enemies may have important demographic consequences (Miller‐Rushing, Hoye, Inouye, & Post, ). Such mismatches have been observed to reduce food availability and consequently breeding success and population size in birds (Both, Bouwhuis, Lessells, & Visser, ; Saino et al, ; Visser, Holleman, & Gienapp, ; but see Franks et al, ) and mammals (Plard et al, ). Empirical analyses of insect population responses to trophic mismatch have, however, received less attention, although there are some studies related to: (a) pests, for example, mismatch with natural enemies which leads to reduced parasitism rates (Evans, Carlile, Innes, & Pitigala, ); (b) Lepidoptera, for example, larvae mismatch with host plants leading to local extinctions (McLaughlin, Hellman, Boggs, & Ehrlich, ), for example, adverse demographic impacts of mismatch in timing of egg hatching in winter moth Operophtera brumata and host plant phenology driving rapid adaptive responses in egg hatching (Van Asch, Salis, Holleman, van Lith, & Visser, ); and (c) pollinators, for example, mismatch of bee emergence with temporal distribution of floral resources (Ogilvie et al, ).…”

Phenology and productivity in a montane bird assemblage: Trends and responses to elevation and climate variation

“…Understanding effects of climate on populations is urgently needed to inform effective conservation and habitat management that promotes resilience to climate change. Climate change may disrupt synchrony between arrival on breeding territories (for migratory species) or initiation of breeding activities, and the availability of resources needed for successful reproduction (Burgess et al, 2018;Franks et al, 2018;Mayor et al, 2017;Møller, Rubolini, & Lehikoinen, 2008). These phenological mismatches, if they occur, could lead to reduced reproductive success and population declines (Dunn & Møller, 2014;Miller-Rushing et al, 2010;Møller et al, 2008).…”

Population responses of bird populations to climate change on two continents vary with species’ ecological traits but not with direction of change in climate suitability

“…to 1980s occurrence data and the 1961-1990 values of the three bioclimate variables. The four SDM types used were generalized linear models(GLMs, McCullagh and Nelder 1989), semiparametric generalized additive models (GAMs, Hastie and Tibshirani 1990), generalized boosted models (GBMs,Elith et al 2008) and random forests(RFs, Cutler et al 2007), all of which perform well when compared with other SDM-fitting techniques(Araujo et al 2005;Elith and Leathwick 2009;Franklin 2009;Meynard and Quinn 2007;Wenger and Olden 2012).…”