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opencc-zeroDec 2014View details →

Data from: Genomic tests of the species-pump hypothesis: recent island connectivity cycles drive population divergence but not speciation in Caribbean crickets across the Virgin Islands

Harnessing the power of genomic scans, we test the debated 'species pump' hypothesis that implicates repeated cycles of island connectivity and isolation as drivers of divergence. This question has gone understudied given the limited resolution of past molecular markers for studying such dynamic phenomena. With an average of 32000 SNPs from the genome of 136 individuals from ten populations of a Caribbean flightless ground cricket species (Amphiacusta sanctaecrucis) and a complementary set of statistical approaches, we infer a stepping-stone colonization model and high levels of genetic differentiation across the Virgin Islands, which have been periodically inter-connected until 8 ka. Estimates of divergence times from models based on the site frequency spectrum coincide with a period of repeated connection and fragmentation of the islands at 75–130 ka. These results are consistent with a role of island connectivity cycles in promoting genomic divergence and indicate that the genetic distinctiveness of island populations has persisted despite subsequent and extended interisland connections identified from bathymetric data. We discuss these findings in the broader context of Caribbean biogeography, and more specifically why high levels of genomic divergence across the Virgin Islands associated with repeated connectivity cycles do not actually translate into species diversification.

opencc-zeroDec 2010View details →

Data from: Climate effects on life cycle variation and population genetic architecture of the black bean aphid, Aphis fabae

Aphid species commonly have different reproductive modes ranging from cyclical to obligate parthenogenesis. The distribution of life cycle variation in aphids is generally determined by ecological forces, mainly climate, because only sexually produced diapausing eggs can survive harsh winters. Aphids are thus interesting models to investigate intrinsic and environmental factors shaping the competition among sexual and asexual lineages. We conducted a Europe-wide sampling of black bean aphids, Aphis fabae, and combined population genetic analyses based on microsatellite data with an experimental determination of life cycle strategies. Aphids were collected from broad beans (Vicia faba) as well as some Chenopodiaceae, but we detected no genetic differentiation between aphids from different host plants. Consistent with model predictions, life cycle variation was related to climate, with aphids from areas with cold winters investing more in sexual reproduction than aphids from areas with mild winters. Accordingly, only populations from mild areas exhibited a clear genetic signature of clonal reproduction. These differences arise despite substantial gene flow over large distances, which was evident from a very low geographic population structure and a lack of isolation-by-distance among 18 sites across distances of more than 1000 kilometres. There was virtually no genetic differentiation between aphids with different reproductive modes, suggesting that new asexual lineages are formed continuously. Indeed, a surprising number of A. fabae genotypes even from colder climates produced some parthenogenetic offspring under simulated winter conditions. From this we predict that a shift to predominantly asexual reproduction could take place rapidly in under climate warming.

opencc-zeroDec 2013View details →

Data from: Overcompensation and phase effects in a cyclic common vole population: between first and second-order cycles

1. Population cycles in voles are often thought to be generated by one-year delayed density-dependence on the annual population growth rate. In common voles, however, it has been suggested by Turchin (2003) that some populations exhibit first-order cycles, resulting from strong overcompensation (i.e. carrying capacity overshoots in peak years, with only an effect of the current year abundance on annual growth rates). 2. We focus on a common vole (Microtus arvalis) population from western France, that exhibits 3-year cycles. Several overcompensating nonlinear models for populations dynamics are fitted to the data, notably those of Hassell, and Maynard-Smith and Slatkin. 3. Overcompensating direct density-dependence (DD) provides a satisfactory description of winter crashes, and one-year delayed density-dependence is not responsible for the crashes, thus these are not classical second-order cycles. A phase-driven modulation of direct density-dependence maintains a low-phase, explaining why the cycles last three years instead of two. Our analyses suggest that some of this phase-dependence can be expressed as one-year delayed DD, but phase-dependence provides a better description. Hence modelling suggests that cycles in this population are first-order cycles with a low phase after peaks, rather than fully second-order cycles. 4. However, based on the popular log-linear second-order autoregressive model, we would conclude only that negative delayed density-dependence exists. The additive structure of this model cannot show when delayed DD occurs (here, during lows rather than peaks). Our analyses thus call into question the automated use of second-order log-linear models, and suggests that more attention should be given to non-(log)linear models when studying cyclic populations. 5. From a biological viewpoint, the fast crashes through overcompensation that we found suggest they might be caused by parasites or food rather than predators, though predators might have a role in maintaining the low phase and spatial synchrony.

opencc-zeroDec 2021View details →

Population specific annual cycles and migration strategies in a leap-frog migrant

A common migratory pattern in birds is that northerly breeding populations migrate to more southerly non-breeding sites compared to southerly: a pattern called leap-frog migration. Not only do populations experience differences in migration distances, but also different environmental conditions, which may vary spatiotemporally within their annual cycles, crating distinctive selective pressures and migratory behaviors. Information on how populations schedule their annual cycles according to environmental conditions and by extension, adapt their migratory behaviors is important to understand drivers of migration and evolution of migration patterns at large. Here we use light level geolocators and citizen science data on regional spring arrivals to compare two populations of common ringed plover Charadrius hiaticula – a textbook example of a leap-frog migrant – breeding at different latitudes. We 1) describe and characterize the spatiotemporal patterns of the annual cycles, and 2) test predictions regarding speed and timing of migration derived from the population specific characterizations of the annual cycles. Winter distributions followed a leap-frog migration pattern, i.e. northern breeding population (NBP) wintered in W Africa and the southern (SBP) mainly in W Europe. The annual cycles were shifted temporally so that the NBP was always later in all stages compared to the SBP. The SBP spent more than twice as long time in the breeding area, but there was no difference in winter residency. There was no difference in migration duration, nor migration speed, between the two seasons within population, but the NBP spent more time on migration in both seasons and migrated faster in spring compared to the SBP. We also found a larger variation in spring arrival times across years in the SBP. This suggests that a complex interaction of population specific timing and variation of breeding onset, length of breeding season and proximity to the breeding area shape the annual cycle and migratory behaviors.

opencc-zeroFeb 2022View details →

Data from: Balancing food acquisition and predation risk drives demographic changes in snowshoe hare population cycles

Snowshoe hare cycles are one of the most prominent phenomena in ecology. Experimental studies point to predation as the dominant driving factor, but previous experiments combining food supplementation and predator removal produced unexplained multiplicative effects on density. We examined the potential interactive effects of food limitation and predation in causing hare cycles using an individual based food-supplementation experiment over-winter across three cycle phases that naturally varied in predation risk. Supplementation doubled over-winter survival with the largest effects occurring in the late increase phase. Although the proximate cause of mortality was predation, supplemented hares significantly decreased foraging time and selected for conifer habitat, potentially reducing their predation risk. Supplemented hares also lost less body mass which resulted in the production of larger leverets. Our results establish a mechanistic link between how foraging time, mass loss, and predation risk affect survival and reproduction, potentially driving demographic changes associated with hare cycles.

opencc-zeroOct 2022View details →

Drivers of winter population cycles in the varied thrush Ixoreus naevius

The drivers of year-to-year difference in winter abundance patterns, particularly dramatic in the "eruptions" of many boreal seed-eating birds, are poorly understood. Varied Thrush (Ixoreus naevius Gmelin, 1789), endemic to the Pacific Northwest of North America, is a boreal species that exhibits pronounced, often biennially cyclic, changes in winter abundance within most of its normal wintering range. Although the drivers of this variability have not previously been explored, it has been suggested that differences in acorn abundance, a key winter food resource, might be important. Here we examine three hypotheses for the drivers of this pattern: the acorn crop within the bird's normal winter range, weather within the bird's winter range, and weather during the previous breeding season within the bird's breeding range. Analyses supported the importance of breeding season conditions, particularly breeding season rainfall, with more birds wintering following wetter years. No support was found for the hypotheses that winter conditions, neither the acorn crop nor winter weather, correlate with winter abundance patterns. For this forest species, year-to-year differences in winter abundance patterns is apparently not driven by the "pull" of winter food supply or winter conditions, but by environmental factors during the prior breeding season that presumably affect reproductive success and subsequent population size.

opencc-zeroDec 2015View details →

Data from: Using a full annual cycle model to evaluate long-term population viability of the conservation-reliant Kirtland's warbler after successful recovery

Long-term management planning for conservation-reliant migratory songbirds is particularly challenging because habitat quality in different stages and geographic locations of the annual cycle can have direct and carry-over effects that influence the population dynamics. The Neotropical migratory songbird Kirtland's warbler Setophaga kirtlandii (Baird 1852) is listed as endangered under the U.S. Endangered Species Act and Near Threatened under the IUCN Red List. This conservation-reliant species is being considered for U.S. federal delisting because the species has surpassed the designated 1000 breeding pairs recovery threshold since 2001. To help inform the delisting decision and long-term management efforts, we developed a population simulation model for the Kirtland's warbler that incorporated both breeding and wintering grounds habitat dynamics, and projected population viability based on current environmental conditions and potential future management scenarios. Future management scenarios included the continuation of current management conditions, reduced productivity and carrying capacity due to the changes in habitat suitability from the creation of experimental jack pine Pinus banksiana (Lamb.) plantations, and reduced productivity from alteration of the brown-headed cowbird Molothrus ater (Boddaert 1783) removal programme. Linking wintering grounds precipitation to productivity improved the accuracy of the model for replicating past observed population dynamics. Our future simulations indicate that the Kirtland's warbler population is stable under two potential future management scenarios: (i) continuation of current management practices and (ii) spatially restricting cowbird removal to the core breeding area, assuming that cowbirds reduce productivity in the remaining patches by ≤41%. The additional future management scenarios we assessed resulted in population declines. Synthesis and applications. Our study indicates that the Kirtland's warbler population is stable under current management conditions and that the jack pine plantation and cowbird removal programmes continue to be necessary for the long-term persistence of the species. This study represents one of the first attempts to incorporate full annual cycle dynamics into a population viability analysis for a migratory bird, and our results indicate that incorporating wintering grounds dynamics improved the model performance.

Figure 6 in Life cycle and population structure of the terrestrial isopod Hemilepistus klugii (Brandt, 1833) (Isopoda: Oniscidea) in Iran

Figure 6. Correlation between cephalothorax width and egg number in ovigerous females of Hemilepistus klugii from Varamin.

Figure 4 in Life cycle and population structure of the terrestrial isopod Hemilepistus klugii (Brandt, 1833) (Isopoda: Oniscidea) in Iran

Figure 4. Frequency distribution of cephalothorax width in Hemilepistus klugii from Varamin from February 2008 to May 2009. Same key as Figure 1.

Figure 3 in Life cycle and population structure of the terrestrial isopod Hemilepistus klugii (Brandt, 1833) (Isopoda: Oniscidea) in Iran

Figure 3. Frequency of ovigerous, post-ovigerous and non-ovigerous females in Hemilepistus klugii during the breeding season (March–April 2008 and 2009) from Varamin based on weekly sampling.

Figure 1 in Life cycle and population structure of the terrestrial isopod Hemilepistus klugii (Brandt, 1833) (Isopoda: Oniscidea) in Iran

Figure 1. Frequency distribution of overall cephalothorax width in Hemilepistus klugii from Varamin.