Disentangling the processes affecting spatial synchrony is challenging but essential to predict the effects of changing environmental conditions on populations. By studying spatial synchrony in density dynamics with and without accounting for the effects of temperature and density dependence, the authors show how temperature synchronizes while density dependence desynchronizes population dynamics.

Abstract

Disentangling empirically the many processes affecting spatial population synchrony is a challenge in population ecology. Two processes that could have major effects on the spatial synchrony of wild population dynamics are density dependence and variation in environmental conditions like temperature. Understanding these effects is crucial for predicting the effects of climate change on local and regional population dynamics. We quantified the direct contribution of local temperature and density dependence to spatial synchrony in the population dynamics of nine fish species inhabiting the Barents Sea. First, we estimated the degree to which the annual spatial autocorrelations in density are influenced by temperature. Second, we estimated and mapped the local effects of temperature and strength of density dependence on annual changes in density. Finally, we measured the relative effects of temperature and density dependence on the spatial synchrony in changes in density. Temperature influenced the annual spatial autocorrelation in density more in species with greater affinities to the benthos and to warmer waters. Temperature correlated positively with changes in density in the eastern Barents Sea for most species. Temperature had a weak synchronizing effect on density dynamics, while increasing strength of density dependence consistently desynchronised the dynamics. Quantifying the relative effects of different processes affecting population synchrony is important to better predict how population dynamics might change when environmental conditions change. Here, high degrees of spatial synchrony in the population dynamics remained unexplained by local temperature and density dependence, confirming the presence of additional synchronizing drivers, such as trophic interactions or harvesting.

This paper provide concepts for quantitative and rapid assessment of resilience of communities in a changing environment.

Abstract

We propose that the ecological resilience of communities to permanent changes of the environment can be based on how variation in the overall abundance of individuals affects the number of species. Community sensitivity is defined as the ratio between the rate of change in the log expected number of species and the rate of change in the log expected number of individuals in the community. High community sensitivity means that small changes in the total abundance strongly impact the number of species. Community resistance is the proportional reduction in expected number of individuals that the community can sustain before expecting to lose one species. A small value of community resistance means that the community can only endure a small reduction in abundance before it is expected to lose one species. Based on long-term studies of four bird communities in European deciduous forests at different latitudes large differences were found in the resilience to environmental perturbations. Estimating the variance components of the species abundance distribution revealed how different processes contributed to the community sensitivity and resistance. Species heterogeneity in the population dynamics was the largest component, but its proportion varied among communities. Species-specific response to environmental fluctuations was the second major component of the variation in abundance. Estimates of community sensitivity and resistance based on data only from a single year were in general larger than those based on estimates from longer time series. Thus, our approach can provide rapid and conservative assessment of the resilience of communities to environmental changes also including only short-term data. This study shows that a general ecological mechanism, caused by increased strength of density dependence due to reduction in resource availability, can provide an intuitive measure of community resilience to environmental variation. Our analyses also illustrate the importance of including specific assumptions about how different processes affect community dynamics. For example, if stochastic fluctuations in the environment affect all species in a similar way, the sensitivity and resistance of the community to environmental changes will be different from communities in which all species show independent responses.

A chapter in the story of a Scottish Peregrine population can now be told in its entirety. Using a 75-year dataset, we show that the reproductive output of Peregrines in southern Scotland was greatly curtailed by organochlorine pesticides. After these chemicals were banned from agricultural use in the 1980s, Peregrine reproductive performance improved substantially and the population recovered. Photo credit: Peter Beasley.

Abstract

Populations of some fish- and meat-eating birds suffered dramatic declines globally following the introduction of organochlorine pesticides during the late 1940s and 1950s. It has been hypothesised that these population declines during the 1950s–1970s were largely driven by a combination of reproductive failure due to eggshell-thinning, egg breakage and embryonic death attributable to DDT and its metabolites, and to enhanced mortality attributable to the more toxic cyclodiene compounds such as aldrin and dieldrin. Using 75 years (1946–2021) of Peregrine falcon (Falco peregrinus) monitoring data (315 unique nest-sites monitored for 6110 nest-years), we studied the breeding performance of a resident Peregrine population in southern Scotland relative to the spatiotemporal pattern of organochlorine pesticide use. We show that (i) Peregrine breeding success and measures of breeding performance increased substantially following the reduction in, and subsequently a complete ban on, the use of organochlorine pesticides; (ii) improvements in Peregrine breeding performance were more dramatic in southeastern Scotland where agriculture was the predominant land use than in southwestern Scotland where there was less arable and more forested land; (iii) Peregrines nesting closer to the coast generally had higher fledging success (that is, a higher proportion of clutches that produced at least one fledgeling) than those nesting inland farther away from the coast; (iv) low temperatures and excessive rain in May negatively affected Peregrine fledging success; and (v) Peregrine abundance increased in parallel with improvements in reproductive performance following the reduction and then complete ban on the use of organochlorine pesticides in the UK. However, recovery was gradual and occurred over four decades, and rate of recovery varied among measures of reproductive performance (egg, nestling and fledgeling production). Our results suggest that the temporal pattern of organochlorine pesticide use strongly influenced Peregrine reproductive parameters but that the pattern of influence differed regionally. Overall results are consistent with the hypothesis that reproductive failure caused by organochlorine pesticides was an important driver of the decline in the south Scottish Peregrine population, and that improvements in all measures of breeding performance following a reduction and eventual ban on organochlorine use facilitated the observed increase in this population.

Abstrakt

Nachdem in den späten 1940er und 1950er Jahren chlororganische Pestizide eingeführt wurden, erlitten die Populationen einiger fisch- und fleischfressender Vögel weltweit einen dramatischen Rückgang. Es wurde die Hypothese formuliert, dass diese- Populationsrückgänge von den 1950er bis in die 1970er Jahre größtenteils auf eine Kombination aus einer reduzierten Fortpflanzungsleistung wegen des Einsatzes des Insektizids DDT mit seinen Metaboliten und den damit verbundenen negativen Auswirkungen (dünnschalige, zerbrechende Eier und Tod der Embryonen) sowie einer erhöhten Mortalität aufgrund der giftigeren Cyclodiene wie Aldrin und Dieldrin zurückzuführen waren. Anhand von Daten aus 75 Beobachtungsjahren (1946–2021) am Wanderfalken (Falco peregrinus) (315 Niststandorte wurden über 6.110 Nestjahre überwacht), untersuchten wir die Fortpflanzungsleistung einer in Südschottland beheimateten Wanderfalkenpopulation und wie sie sich in Relation mit einem zeitglichen Einsatz von chlororganischen Pestiziden entwickelt hat. Wir zeigen, dass: (i) der Bruterfolg des Wanderfalken nach der Reduzierung und dem anschließenden vollständigen Verbot von chlororganischen Pestiziden erheblich zunahm; (ii) der Bruterfolg des Wanderfalken im Südosten Schottlands stärker anstieg, wo Landwirtschaft die vorherrschende Landnutzung ist, als in Südwesten Schottlands, wo es weniger Agrargebiete und mehr Waldland gab; (iii) Wanderfalken die näher an der Küste nisteten eine höhere Produktivität (Anzahl flügger Jungvögel pro Brutversuch) aufwiesen als solche, die weiter von der Küste entfernt im Landesinneren nisteten; (iv) sich niedrige Temperaturen und überdurchschnittlich hohe Regenfälle im Mai negativ auf den Fortpflanzungserfolg auswirkten, und (v) die Anzahl der Wanderfalken in Südschottland, parallel zu einer Verbesserungen der Fortpflanzungsleistung nach Reduktion bzw. vollständigem Verbot des Einsatzes von chlororganischen Pestiziden im Vereinigten Königreich, zunahm. Diese Erholung verlief jedoch schrittweise und erfolgte über einen Zeitraum von vier Jahrzehnten, wobei die Erholungsrate je nach Maß für die Reproduktionsleistung (i.e. Anzahl der Eier, Bruterfolg, Produktivität) unterschiedlich ausfiel. Unsere Ergebnisse deuten darauf hin, dass der Einsatz von chlororganischen Pestiziden die Reproduktionsparameter der Wanderfalken im Untersuchungsraum stark beeinflusste, die Stärke des Einflusses jedoch regional unterschiedlich war. Die Gesamtergebnisse stimmen mit der Hypothese überein, dass eine durch chlororganische Pestizide verursachte reduzierte Reproduktionsleistung ein wichtiger Faktor für den Rückgang der südschottischen Wanderfalkenpopulation war. Die Verbesserung aller brutbiologischen Kennziffern und der starke Anstieg der Wanderfalken-Population in Südschottland ging mit einer Reduzierung bzw. mit dem gänzlichen Verbot des Einsatzes von chlororganischen Pestiziden einher.

Broader diet breadths enable omnivores to mount dynamic responses feeding to parasite attack, but little is known about how plant/prey mixing might influence responses to infection. These results suggest that a diverse nutritional landscape may be key in enabling omnivores' resistance and resilience to immune stressors in their environments.

Abstract

Diet composition modulates animals' ability to resist parasites and recover from stress. Broader diet breadths enable omnivores to mount dynamic responses to parasite attack, but little is known about how plant/prey mixing might influence responses to infection. Using omnivorous deer mice (Peromyscus maniculatus) as a model, we examine how varying plant and prey concentrations in blended diets influence resistance and body condition following infestation by Rocky Mountain wood ticks (Dermacentor andersoni). In two repeated experiments, deer mice fed for 4 weeks on controlled diets that varied in proportions of seeds and insects were then challenged with 50 tick larvae in two sequential infestations. The numbers of ticks successfully feeding on mice declined by 25% and 66% after the first infestation (in the first and second experiments, respectively), reflecting a pattern of acquired resistance, and resistance was strongest when plant/prey ratios were more equally balanced in mouse diets, relative to seed-dominated diets. Diet also dramatically impacted the capacity of mice to cope with tick infestations. Mice fed insect-rich diets lost 15% of their body weight when parasitized by ticks, while mice fed seed-rich diets lost no weight at all. While mounting/maintaining an immune response may be energetically demanding, mice may compensate for parasitism with fat and carbohydrate-rich diets. Altogether, these results suggest that a diverse nutritional landscape may be key in enabling omnivores' resistance and resilience to infection and immune stressors in their environments.