Predicting Species Range Shifts Under Climate Change

by Cameron Lukos

Global climate change is causing long lasting effects on all of Earth’s natural systems. A consequence of these changes is species range shifting. Accurately predicting these shifts is very difficult and many methods have been criticized. The standard bioclimate envelope models (BEMS) have been criticized as too simple because they do not incorporate biotic interactions or evolutionary adaptation. BEMs are widely used though. Kubish et al. (2013) wanted to determine the evolutionary conditions of dispersal, because local adaptation or interspecific competition may be of minor importance for predicting future shifts. They used individual-based simulations at two different temperatures as well as competing simulations. Their results show that in single-species scenarios excluding adaptation, species follow optimal habitat conditions or go extinct if their connection to the environment becomes too weak. With competitors, their results were dependent on habitat fragmentation. If a species was highly connected to its habitat, the range shifted as predicted; if a species was only moderately connected to its environment, there was a lag time, and with low connectivity to the environment, the result was extinction. Based on this work, Kubisch et al. determined that the BEMs may work well as long as habitats are well connected and there is no difficulty dispersing. Continue reading

Effects of Local Adaptation and Interspecific Competition on Species’ Response to Climate Change

by Cameron Lukos

Adaptations, and how effective the adaptations are, allow species to have varying geographic ranges. For instance, species that have the tolerance to survive in cold climates will be able to live and survive in those conditions while others who do not have that ability will not be found. This gives different geographic ranges for all species. But our world is experiencing global climate change which means that the environments species are presented with will also change. Bocedi et al. (2013) used models to include the effect of climate change coupled with species interactions to understand these changing dynamics. To do this, they created simulations of two competing species across a linear climatic gradient that changes at different latitudes and gets warmer. Bocedi et al. gaged reproductive success by the individual’s adaptation to local climate and its location relative to global constraints. In conducting their experiment they found that in changing the strength of adaptation and competition, competition reduces genetic diversity and slows the rate of range change. They also found that one species can drive the other to extinction long after climate change has occurred. Weak selection of adaptation and low dispersal ability also caused a loss of warmer-adapted phenotypes and that geographic ranges became disjointed and lost centrally adapted genotypes. Continue reading

High and Distinct Range-Edge Genetic Diversity despite local Bottlenecks

 

by Cameron Lukos

The genetic consequences of being at the edge of species ranges has been the subject of much debate. Populations that occur at low latitude ranges are expected to retain high unique genetic diversity. Less favorable environments that limit population size at the range edges may have caused genetic erosion that has a stronger effect than past events. This study by Assis et al. (2013) provided a test of whether the population declines at the peripheral range might be shown in decreasing diversity and increasing population isolation and differentiation. The authors compared population genetic differentiation and diversity with trends in abundance along a latitudinal gradient to the furthest extents of the range of a sea kelp, Saccorhiza polyschides. Assis et al. also looked at recent bottleneck events to determine whether the recent recoded distributional shifts had a negative impact on the population size. They found that there was decreasing population density and increasing spatial fragmentation and local extinction at the southern edge. The genetic data revealed two distinct groups and a central mixed group. As the authors had predicted there was higher differentiation and evidence of bottleneck at the southern edge but instead of a decrease there was an increase in genetic diversity suggesting that extinction and recolonization had not reduced diversity and that this may be evidence of a process of shifting genetic baselines. Continue reading

Climate Change Forces Species to Shift Niches

 

by Cameron Lukos

In order for species to survive environmental change and avoid extinction, they have to be able to either track suitable environmental conditions or adapt to the changed environment.  Whether and how species adapt to environmental change is largely unknown.  Wasof et al. (2013) examined specifically the realized niche width (ecological amplitude), and the realized niche position (ecological optimum).  A realized niche is the actual space that a species inhabits and the resources it can access as a result of limiting biotic factors present in the habitat.  They created the niche width from a beta diversity metric, which increases if the focus species co occurs with other species.  Wasof et al. used a detrended correspondence analysis (DCA) to represent the locations of the niche positions and then developed their own approach to run species specific DCAs to allow the focal species to shift its realized niche while others stayed put.  Wasof et al. concluded that none of the 26 species maintained their realized niche width and position along the latitudinal gradient.  A few species shifted their realized niche width but all of the species shifted their position.  Most of the species that shifted their position shifted their realized niche for areas where soil nutrients and pH were poorer and more acidic.  The results suggest that these plants are locally adapting or have plasticity.  The pattern Continue reading

Antarctic Sea Ice Changes Affect Krill, the Marine Food Base

by Cameron Lukos

Flores et al. 2013, hoped to create a synoptic investigation that showed seasonal changes in depth distribution of macrozooplankton and micronekton and their relationship to environment. They used data from three different expeditions that were part of a larger multi-year experiment that sailed the Lazzarev Sea collecting data on Antarctic krill in the Lazzarev Sea, creating an inventory of the pelagic macrozooplankton and micronekton from the surface down to 3000 meters, and exploring the seasonal changes in depth distribution and the relationship between communities and environmental drivers. The samples were collected via trawl nets at varying depths up to 3000 m and were done at different times of the year in order to run statistical analysis. Flores et al. found that the majority of the species sampled were found in the deep layer at depths that have not previously been studied, but there also was a higher number of species in the epipelagic layer than has been previously recorded. The higher richness in the epipelagic layer may confirm that the differences in species composition were caused by higher sampling effort or by species avoiding the surface layer. When the authors compared seasons with depth layer there were significant differences. In one instance there was a large dissimilarity between the surface layer and the overlapping epipelagic layer in each season.

Flores H., Hunt B., Kruse S., Pakhomov E., Siegel V., van Franeker J., Strass., Van de Putte A., Meesters E., Bathmann U., 2014. Seasonal Changes in the Vertical Distribution and Community Structure of Antarctic Macrozooplankton and Micronekton. Deep- Sea Research 1 84, 127–141. http://goo.gl/DB72rX

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Population Growth in a Wild Bird is Buffered Against Phenological Mismatch

It is well understood that global climate change is having effects on various species, but there are few studies that have quantified the costs of sustained directional selection in response to global climate change.  Reed et al. conducted a study to test whether the population growth of Parus major (great tit) was negatively affected by climate change.  Specifically, to see if climate change induced a phenological mismatch.  They took four decades of individual level life history data from a population of great tits in the Netherlands whose breeding season is closely tied with the development of caterpillars as a food source to feed the young birds.  Caterpillar growth is closely linked to warm temperatures which are critical to the breeding success of the great tit.  Due to warmer springs there has been a mismatch of the breeding time and the food peak creating an intensification of direction selection to earlier laying dates.  This mismatch has not affected the population growth.  Reed et al. demonstrate a mechanism that contributes to the decoupling; that fitness losses due to the mismatch are countered by fitness gains due to less competition.  It implies that populations may be able to tolerate maladaptation from climate without immediately declining. Cameron Lukos

Reed, T.E., Grøtan, V., Jenouvrier, S., Sæther, B.-E., Visser, M.E., 2013. Population Growth in a Wild Bird Is Buffered Against Phenological Mismatch. Science 340, 488-491.

                  To conduct their study, Reed et al. studied a population of Parus major in relation to a food source of caterpillars.  The focus area has experienced spring warming in recent decades due to climate change.  The birds rely on caterpillars as a food source for the fledglings and so match their breeding patterns with the seasonal peak of caterpillars.  The experimenters ran a statistical analysis to test how strong their connection is with the mismatch affecting population growth.  When their results showed no statistical significance, the experimenters created a fitness variable to further understand the decoupling of population growth. 
                  Their results show that warmer temperatures create a larger mismatch between caterpillars and the tits.  But there was no statistical significance with either analysis.  The mismatch had no statistically significant connection between the population growth and directional selection.  The addition of fitness also did not yield any statistical significance.  The lack of statistical significance reveals that there is something further that has not been accounted for.  The question becomes why is population growth not lower in years with a large fraction of females lay too late?  Reed et al. discuss two reasons for this.  One is that the food peak is much narrower than the distribution of breeding dates and so reproductive fitness cannot be high for all females every year.  The experimenters show that in an early reproductive year relative to food peaks, females who start early produced fewer fledglings than females that started later.  Those females that started in the middle had the highest reproductive output.  In a relatively late reproductive year late females had lower reproductive output than intermediates.  The ones who do the best in this situation are those that reproduce early.  This pattern is most likely due to the fact that some pay a higher energetic costs when feeding their broods.  The second reason is that fledgling production is counterbalanced by improved independent survival of offspring due to relaxed competition.

http://www.sciencemag.org/content/340/6131/488.short

Evolutionary Rescue from Extinction is Contingent on a Lower Rate of Environmental Change

Natural selection is defined as the method that allows species to persist and survive in an ever changing world.  But natural selection is a very long and slow process, so rapidly changing environments will hinder the ability of natural selection to keep species alive.  Lindseyet al. 2013 used the bacteria Escherichia coli to prove that rapid climate change will hinder the process of natural selection and may therefore cause extinction.  Although some experiments have shown that slower rates of environmental change have led to more adapted populations or fewer extinctions.  Lindsey et al. used different concentrations of the antibiotic, rifampicin with E. coli over different time periods to simulate slow, intermediate and rapid environmental change.  They then genetically created all possible combinations of mutations that can result from slow rates of environmental change.  The assessment of the engineered strains show that certain genotypes are evolutionarily inaccessible under rapid environmental change, and that rapid change could eliminate entire sets of mutations as options.  They further speculated that intermediate levels of change might enhance expressions of genes, then there could be more endpoints as a result.  This could have an effect on rates of adaptation that could among other things, increase rate of development of antibiotic resistance. —Cameron Lukos

Lindsey, H.A., Gallie, J., Taylor, S., Kerr, B., 2013. Evolutionary rescue from extinction is contingent on a lower rate of environmental change. Nature 494, 463–467.

                  The experiment was carried out by propagating 1,255 populations of E. coli.  The experimenters also created mutants to add the secondary factor of selective accessibility.  These populations were then placed under increasing amounts of the antibiotic rifampicin.  The treatments had different rates of change, ranging from sudden to gradual.  The populations all started in an antibiotic free environment and ended at a maximum concentration of 190µg/ml.  The populations that were subject to rapid change were exposed to the maximum rifampicin concentration after the first transfer and remained at that level for the rest of the experiment.  Populations exposed to moderate change received the maximum amount of rifampicin halfway through the experiment and the populations exposed to gradual changed experienced the full amount of rifampicin on the last transfer of the experiment.
                  The results indicate that as the rate of environmental change increased the number of populations that survived the whole experiment decreased.  Populations exposed to gradual change were able to become resistant to the antibiotic because there was more time for mutations to occur and spread.  They also found that there were significant differences in growth rates of the populations exposed to gradual and sudden change, indicating that different mutations occurred in different treatments.  For instance, in the case of the sudden populations only one mutation was detected, while in the moderate and gradual populations many different mutations were discovered.  Lindsey et al. found a clear historical contingency for mutations that occurred in the intermediate environments.  It suggests that the mutations allow for the lineage to gain other mutations, a historical contingency.  From this, the results suggest the high rates of climate change will cause problems for species resulting in higher extinction rates.  Not only will it wipe out genetic diversity but it may also result in the loss of potential mutations that could occur under less extreme conditions.
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Climate Events Synchronize the Dynamics of a Resident Vertebrate Community in the High Arctic

In studying climate, scientists have been furthering their understanding of how climate events have been affecting a particular species.  But it is unclear how climate will affect communities of species as a whole.  Using the high Arctic as a case study, Hansen et al. (2013) describe changes in the weather patterns of Svalbard and how these events synchronize population fluctuations across the entire vertebrate community and cause a lagged effect on a secondary consumer, the arctic fox.  The synchronization of populations is theorized to occur when winter rains turn to ice, causing the vegetation to be encased in ice and therefore unavailable by herbivores.  This indirect bottom up forcing drives population dynamics across the vertebrates in Svalbard.  With global warming, such icing is expected to become more frequent in the Arctic and therefore strongly affect terrestrial ecosystems.  Hansen et al used statistical data based on population fluctuations and weather to demonstrate the effects of severe weather events on mixed populations. —Cameron Lukos

Hansen, B.B., Grøtan, V., Aanes, R., Sæther, B.-E., Stien, A., Fuglei, E., Ims, R.A., Yoccoz, N.G., Pedersen, Å.Ø., 2013. Climate events synchronize the dynamics of a resident vertebrate community in the high arctic. Science 339, 313—315.  

                  The community Hansen analyzed was the island of Svalbard.  The ecological community consisted of three herbivore species: Svalbard reindeer, Svalbard ptarmagin, vole and the secondary consumer the Arctic fox.  Hansen et al. found correlated population fluctuations of all four species.  The Arctic fox data were advanced one year due to a delayed population reaction to the change in herbivores.  Based on these data, Hansen et al. hypothesized that the climate events were affecting the plant species which limited the amount of forgeable food for herbivores.  This creates a bottom up effect which then causes dips in the arctic fox population.  In order to test this hypothesis, Hansen et al. ran linear regressions that modeled population growth rates as a function of population size and precipitation events.

                  The authors determined that after factoring in density dependence, number of rainy days in the winter months was the best predictor of annual population growth rates across species.  Winter rains caused a negative effect on all species.  Hansen et al. also found that summer temperatures had a positive effect on species growth rates.  This confirmed their hypothesis that climate events do enforce synchrony among herbivores and causes the lag response of artic foxes.  Increased summer temperatures increase green foliage which in turn supplies more food for herbivores and thus an increase in the number of secondary consumers.  Winter rains reduce food supply due to freezing vegetation and the soils.  This then causes increased mortality rates of old sick and very young individuals.  The changing mortality rates cause a decline in population followed by an increase due to less competition and in the case of ptarmagins and voles a drop in predation.