Wake Of Invasion Research Articles

Population dynamics of ash across the eastern USA following invasion by emerald ash borer

Non-native insects and pathogens can alter the composition and successional trajectories of forests and, in exceptional cases, drive their host trees functionally extinct. Emerald ash borer has killed millions of ash trees in its invaded range across eastern North America. Predicting the future ecological role of ash requires information on the extent of ash regeneration and recruitment in the wake of invasion. Variable levels of ash regeneration have been observed in stands invaded by emerald ash borer, although recruitment rates of young ash trees into the overstory remain unclear. Here, we used forest inventory data to quantify ash recruitment and regeneration across the eastern United States, and we linked these observed patterns to emerald ash borer invasion history. Inventory data from 2013-2018 indicate there has been extensive ash regeneration in invaded regions, totaling > 1,200 seedlings per ha in counties invaded in 2002–2006. Plots in counties with the longest invasion histories contained the highest densities of ash seedlings and saplings, likely due to the high densities of overstory ash in these areas prior to invasion by emerald ash borer. Seedling densities also remained generally unchanged between inventory periods ending in 2007 and 2018 irrespective of invasion history. Despite this widespread regeneration, ash trees in the smallest overstory class died at faster rates than they were recruited from seedlings or saplings, resulting in negative population trajectories on plots that have been invaded for more than ~ 10 years. This trend suggests that ash will continue to decline in abundance and may become functionally extinct across the invaded range of emerald ash borer. However, the future ecological role of ash will ultimately be determined by the iterative production and survival of ash seeds to reproductive ages in the presence of emerald ash borer populations, along with effective management practices.

Campaigns on the Home Front: Norwegian-American Farmers and Workers Mobilized for War

52 Campaigns on the Home Front N O RW EG I AN -­AMERICA N FA RMERS A ND WO R K ER S MOB ILIZED FOR WA R Ann Marie Legreid “ But there is one front and one battle where everyone in the United States, every man, woman, and child . . . is in action. That front is right here at home.”1 —­ president franklin d. roosevelt, 1942 Norwegians and Norwegian Americans were united as never before by the ideals of liberty in the wake of the Nazi invasion of Norway on April 9, 1940. The free world and its basic human freedoms were at stake. The citizens of Stoughton, Wisconsin, were “outraged” at the “ruthless invasion of Norway” which had “all the earmarks of piracy.”2 Sunday, April 21, 1940, was declared a day of prayer for the people of Norway and their royal family by Norwegian Lutheran congregations across America. Norwegian Americans incorporated American Relief for Norway within ten days of the Nazi invasion. The Nazi occupation (1940–­ 1945) generated 53 campaigns on the home front both sympathy and support for the Norwegian people among Norwegian Americans . Norwegian Americans were intimately and passionately involved in wartime efforts on the home front and on the frontlines, revealing strong and enduring ties to a beloved motherland. From confusion and despair, a united and determined people emerged with the common cause of liberty. King Haakon, speaking to the Norwegian people in 1940 via radio from Northern Norway on the Norwegian national holiday, the Seventeenth of May, said: “For more than a hundred years this day has united the people of Norway in the idea of liberty and the work of liberty accomplished at Eidsvold, where we all promised one another to defend this country.” The King’s monogram H7 became the symbol of liberty. C. J. Hambro, president of the Norwegian parliament , wrote in the wake of the invasion: “And so the Government urges the whole nation to safeguard the inheritance of freedom, faithful to the great ideas which have carried Norway through the centuries. Long live the fatherland! Long live a free Norway!”3 In 1940 Norwegians in America were heavily concentrated in urban areas and farming communities in the Upper Midwest. Minneapolis and Chicago were the undisputed centers for Norwegian-­ American organizational life. The earliest settlements were planted in northern Illinois and southern Wisconsin in the mid-­ nineteenth century. Eventually, colonies emerged across the United States and Canada, in Minnesota, Iowa, Nebraska, Kansas, Michigan, the Dakotas , the Canadian prairies, Texas, Washington, California, Vancouver, and New York. The great transatlantic migrations brought more than 900,000 Norwegians to the United States from 1825 to the present day, with 87 percent of them migrating between 1865 and 1930. Thus, connections to the motherland were vibrant and meaningful when war came to Norway in 1940.4 Wartime stresses and strains brought solidarity to Norwegian Americans from all walks of life, heightened their patriotic spirit as Americans, and provided new opportunities for them in areas such as business, industry, and agricultural production. Home-­front campaigns were organized across America by innumerable ethnic, charitable, and community groups. Norwegian Americans, like their ethnic neighbors, joined the home-­ front campaigns in very personal and generous ways. 54 articles Norwegian Americans served alongside their fellow Americans on the battlefield as well. In doing so, they brought heightened visibility in the United States to the plight of the people in occupied Norway.5 In September 1942 President Roosevelt noted the resilience and resistance of the Norwegian people in his famous words to the free world delivered in Washington, D.C., from his open car, with Princess Märtha at his side, “Look to Norway!”6 Roosevelt’s Four Freedoms speech posited moral obligations that transcended national and ethnic boundaries : freedom from fear, freedom from want, freedom of speech, and freedom of worship. The Four Freedoms were the subject of iconic paintings by Norman Rockwell replicated on calendars and posters and displayed ubiquitously in homes and public places across America. Throughout the war these hung as important visual reminders of the basic freedoms at stake.7 Americans engaged in the war effort fought for the universal values of life, liberty, and...

Correction: In the Wake of Invasion: Tracing the Historical Biogeography of the South American Cricetid Radiation (Rodentia, Sigmodontinae)

Correction: In the Wake of Invasion: Tracing the Historical Biogeography of the South American Cricetid Radiation (Rodentia, Sigmodontinae)

In the wake of invasion: tracing the historical biogeography of the South American cricetid radiation (Rodentia, Sigmodontinae).

The Great American Biotic Interchange (GABI) was greatly influenced by the completion of the Isthmus of Panama and impacted the composition of modern faunal assemblages in the Americas. However, the contribution of preceding events has been comparatively less explored, even though early immigrants in the fossil records are evidence for waif dispersals. The cricetid rodents of the subfamily Sigmodontinae are a classic example of a species-rich South American radiation resulting from an early episode of North American invasion. Here, we provide a temporal and spatial framework to address key aspects of the historical biogeography and diversification of this diverse mammal group by using mitochondrial and nuclear DNA datasets coupled with methods of divergence time estimation, ancestral area reconstruction and comparative phylogenetics. Relaxed-clock time estimates indicate that divergence of the Sigmodontinae began in the middle–late Miocene (ca. 12–9 Ma). Dispersal-vicariance analyses point to the arrival of a single lineage of northern invaders with a widespread ancestral distribution and imply that the initial differentiation between Central and South America gave rise to the most basal groups within the subfamily. These two major clades diversified in the late Miocene followed by the radiation of main tribes until the early Pliocene. Within the Oryzomyalia, tribes diverged initially in eastern South America whereas multiple dispersals into the Andes promoted further diversification of the majority of modern genera. A comparatively uniform background tempo of diversification explains the species richness of sigmodontines across most nodes, except for two akodontine genera with recent increases in diversification rates. The bridging of the Central American seaway and episodes of low sea levels likely facilitated the invasion of South America long before the onset of the post-Isthmian phase of the GABI.

Democracy: The Case for Opportunistic Idealism

George W. Bush’s second inaugural address on January 20, 2005 was clearly written with the history books in mind. In ringing terms, the president proclaimed, ‘‘The survival of liberty in our land increasingly depends on the success of liberty in other lands. The best hope for peace in our world is the expansion of freedom in all the world.’’ 1 The pro-democracy rhetoric of the Bush era, however, already looks hubristic, and even somewhat hypocritical, as a new president prepares to take office in the United States. The sweeping universalism of the language employed by Bush was always vulnerable to qualification, when principle encountered local realities. Certainly in some of the United States’ closest democratic allies, such as India, Israel, and the United Kingdom, there is an increasingly open skepticism about the idea of placing democracy promotion at the heart of foreign policy. The inconsistencies in the foreign policy of the Bush administration have ensured that this skepticism has now entered the domestic debate in the United States as well, making the very idea of democracy promotion overseas controversial. So should a new administration ditch the entire policy? Or are there other, better, ways of pursuing the same goal? Bush’s Inconsistent Freedom Agenda In the United Kingdom, it is a common belief that the attempt to export democracy to Afghanistan and Iraq in the wake of invasions was a mistake. David Cameron, the leader of UK’s Conservative Party, argued on a recent trip to Pakistan that ‘‘we should accept that we cannot impose democracy at the barrel of a gun. We cannot drop democracy from 10,000 feet and we should not

On the persistence of spatiotemporal oscillations generated by invasion

Many systems in biology and chemistry are oscillatory, with a stable, spatially homogeneous steady state which consists of periodic temporal oscillations in the interacting species, and such systems have been extensively studied on infinite or semi-infinite spatial domains. We consider the effect of a finite domain, with zero-flux boundary conditions, on the behaviour of solutions to oscillatory reaction-diffusion equations after invasion. We begin by considering numerical simulations of various oscillatory predator-prey systems. We conclude that when regular spatiotemporal oscillations are left in the wake of invasion, these die out, beginning with a decrease in the spatial frequency of the oscillations at one boundary, which then propagates across the domain. The long-time solution in this case is purely temporal oscillations, corresponding to the limit cycle of the kinetics. Contrastingly, when irregular spatiotemporal oscillations are left in the wake of invasion, they persist, even in very long time simulations. To study this phenomenon in more detail, we consider the λ-ω class of reaction-diffusion systems. Numerical simulations show that these systems also exhibit die-out of regular spatiotemporal oscillations and persistence of irregular spatiotemporal oscillations. Exploiting the mathematical simplicity of the λ-ω form, we derive analytically an approximation to the transition fronts in r and θ x which occur during the die-out of the regular oscillations. We then use this approximation to describe how the die-out occurs, and to derive a measure of its rate, as a function of parameter values. We discuss aplications of our results to ecology, calcium signalling and chemistry.

Periodic travelling waves in a family of deterministic cellular automata

Abstract Reaction-diffusion equations whose kinetics contain a stable limit cycle are an established class of models for a range of biological and chemical systems. In this paper I construct a family of deterministic cellular automata, with nine states, which are qualitatively similar to oscillatory reaction-diffusion equations, in that their rules reflect both local oscillations and spatial diffusion. The automata can be crudely interpreted as models of predator-prey interactions, and I show that the behaviour following local perturbation of the prey-only state in one space dimension is very similar in the automata and in standard reaction-diffusion models for predator-prey systems. In particular, in many cases, invasion of prey by predators leaves behind periodic travelling waves in the wake of invasion. I study in detail these periodic plane waves in the automaton, by explicitly investigating periodic solutions of the difference equation governing travelling waves. I show that the automaton has many different periodic wave solutions, and I compare their properties with those of periodic wave solutions of reaction-diffusion systems. The basic conclusion is that included amongst the periodic waves in the automaton are a family of solutions which mimic quite closely the properties of reaction-diffusion periodic waves.