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Papers by Mark Davis

1 The invasion of habitats by non-native plant and animal species is a global phe-nomenon with po... more 1 The invasion of habitats by non-native plant and animal species is a global phe-nomenon with potentially grave consequences for ecological, economic, and social systems. Unfortunately, to date, the study of invasions has been primarily anecdo-tal and resistant to generalization. 2 Here, we use insights from experiments and from long-term monitoring studies of vegetation to propose a new theory in which fluctuation in resource availability is identified as the key factor controlling invasibility, the susceptibility of an envir-onment to invasion by non-resident species. The theory is mechanistic and quanti-tative in nature leading to a variety of testable predictions. 3 We conclude that the elusive nature of the invasion process arises from the fact that it depends upon conditions of resource enrichment or release that have a vari-ety of causes but which occur only intermittently and, to result in invasion, must coincide with availability of invading propagules. Key-words: plant in...

Charles S. Elton and the dissociation of invasion ecology from the rest of ecology

Ecosphere, 2021

Due to decades of fire suppression, much of the Upper Midwest savanna habitat has converted to oa... more Due to decades of fire suppression, much of the Upper Midwest savanna habitat has converted to oak woodland. In efforts to restore oak savanna habitat, fire has been re‐introduced in many of these woodlands. A primary purpose of these burns is to kill the fire‐sensitive mesophytic tree species, which had established themselves during the decades of fire suppression, reduce the number of understory trees, and preserve the larger more widely spaced oaks. It is clear from ongoing efforts that restoring oak savannas will require frequent fires over decades, but frequent fires over the long term can also threaten the desirable oaks. Long‐term demographic studies at savanna restoration sites experiencing frequent fires are necessary to determine the extent to the frequent burns are supporting and/or confounding restoration goals. Results presented here are from a twenty‐five‐year demographic study of an Upper Midwest bur oak (Quercus macrocarpa) savanna/woodland experiencing frequent fire...

Science, 2000

's News Focus article about the restoration of North America's forests (28 Jan., p. 573) suggests... more 's News Focus article about the restoration of North America's forests (28 Jan., p. 573) suggests to me that it might be time to retire the word "restoration." There are at least three problems with the field of restoration ecology. First is the arbitrariness of determining which time period in the past should be the target of restoration efforts. In the United States, this has typically been assumed to be before settlement by Europeans. But why should that be the target any more than the time before the native Americans settled the region? Perhaps the most common environment in the past 15,000 years should be the target. In Minnesota, this would mean that much of the landscape would be restored to several hundred meters of ice. The second problem is that there is an implication of stasis with the word "restored." Not only do we try to replicate some past environment, but then we try to maintain it in that form through management. Yet nature is not static. The third problem is that true restoration is simply impossible. The climate is no longer the same, and keystone species are absent or new species are present that make it impossible to truly restore the habitat to any prior state. The goals of restoration ecology are certainly worthy ones and have captured the imagination of many of our students who have gone on in careers in the field. What seems to have become outdated is not the passion to better our environment, but the word "restoration" itself. Some students initially attracted to the field end up disenchanted as they come to realize that restoration ecology is at best a fiction and at worst motivated by a particular dominant cultural perspective. "Ecological enhancement" or "ecological enrichment" more accurately describes what we are really doing when we say we are "restoring" a site, and these terms avoid at least some of the assumptions and pretenses inherent in the word "restoration." As a formal discipline, perhaps restoration ecology should become a subdiscipline of landscape architecture and referred to as "ecological architecture." Of course, the goals and methods will still be arbitrary, developed by the various stakeholders, because nature itself provides no specific prescription for human intervention. But "ecological architecture" more aptly describes what we have been doing all along-conceiving and then trying to realize a new vision for a natural landscape.

Frontiers in Ecology and the Environment, 2004

The Society for Ecological Restoration's Science & Policy Working Group define ecological restora... more The Society for Ecological Restoration's Science & Policy Working Group define ecological restoration as the process of assisting the recovery of damaged, degraded, or destroyed ecosys? tems (SER 2002). While ecological restoration involves restoring ecosystems at specific project sites, restoration ecology is the science on which the practice is based, and should ideally provide clear concepts, models, methodologies, and tools to support it. Restoration ecology is still an emerging science, with its roots in practical restoration projects around the world. Research generally focuses on improving the conceptual, technical, and socioeconomic bases for conducting effective ecological restoration. In recent years, there has been a move away from site-and situation-specific studies of particular restoration projects to a broader consideration of the conceptual basis for restoration ecology and the publication of synthetic treatments of the subject (Hobbs and Norton 1996; Whisenant 1999; Hobbs and Harris 2001; Perrow and Davy 2002; Temperton et al. in press). To restore an ecosystem, we need to understand how it worked before it was modified or degraded, and then use this understanding to reassemble it and reinstate essential processes. There is an increasing recognition that ecosystem dynamics can be complex, non-linear, and often unpredictable. The importance of broadscale processes and interactions between adjoining ecosystems adds further complexity, since impacts in one place may be the result of events or management decisions elsewhere. This makes it difficult to correctly diagnose the problems leading to ecosystem degrada? tion or preventing recovery, and to initiate effective corrective or restorative management. The type of intervention required in restoration depends heavily on the type and extent of damage to the ecosystem. In some cases, relatively small changes in the management or manipulation of the species composition are required, as in the removal of harmful invasive species or the replacement of missing species. In other cases, a substantial alteration of the physical cases, and at what cost, is required. In most cases, there will be a range of options that vary in expected outcome and relative cost, and there needs to be a clear ? The Ecological Society of America www.frontierfcinecoiogy.org This content downloaded on Fri, 4 Jan 2013 14:13:00 PM All use subject to JSTOR Terms and Conditions 1996). ? References Bradshaw AD. 1983. The reconstruction of ecosystems. J Appl Ecol 20: 1-17. www.frontiersinecology.org ? The Ecological Society of America This content downloaded on Fri, 4 Jan 2013 14:13:00 PM All use subject to JSTOR Terms and Conditions Forum Restoration ecology: the challenge of social values and expectations Bradshaw AD and Chadwick MJ. 1980. The restoration of land. Oxford, UK: Blackwell Publishing.

Mètode Revista de difusió de la investigació, 2018

In the 1980s, three sub-disciplines of ecology emerged – restoration ecology, conservation biolog... more In the 1980s, three sub-disciplines of ecology emerged – restoration ecology, conservation biology, and invasion biology – and all three embraced the nativism paradigm. By the early 2000s, historians, sociologists, and philosophers interested in the development of science began to examine the growing field of invasion biology and usually were critical of it. In the past few years, a new perspective has been taking hold in the field of ecology. Referred to as ecological novelty it emphasizes that many factors are producing ecologically novel environments. A much more simply descriptive concept, it is currently competing with the nativism paradigm to define nature. Whether the nativism or ecological novelty paradigm emerges as the dominant perspective going forward will determine how nature and biodiversity are managed.

BioScience, 2004

Books foot-tall spruce to see life from a treetop perspective. Swallows migrated to the moon, ass... more Books foot-tall spruce to see life from a treetop perspective. Swallows migrated to the moon, asserted naturalist John Morton in the late 18th century. Heinrich's splendid book gives us a more informed view of animals' adaptations, in this case, the adaptations that enable survival in winter. It is the rare book that teaches us to see more clearly even as it delights us. Winter World will impel you to take a walk in the winter woods.

Oecologia, 1981

The reproductive success and energy budgets of single and multiflowered plants of Trillium erectu... more The reproductive success and energy budgets of single and multiflowered plants of Trillium erectum L. (Liliaceae) were assessed over a period of 4 years. Plants with more than one flower were found to attract more pollinators, to be less vulnerable to predation by Tortricid moths, and to produce more seeds than single flowered plants. Despite the reproductive superiority exhibited by multiflowered plants, most plants (85%) in the population studied were single flowered. It is shown that even though the insect interactions make it advantageous to produce more than one flower, most plants lack the energy to do so. The optimality approach which has guided previous studies of this kind is criticzied.

Oecologia, 1991

The effects of fire and pocket gophers, Geomys bursarius, on the survivorship of Penstemon 9randi... more The effects of fire and pocket gophers, Geomys bursarius, on the survivorship of Penstemon 9randiflorus growing in an oak woodland in Minnesota were studied from 1986 to 1990. Plants growing in sparse vegetation experienced mortality rates twice that of plants growing in dense vegetation. This difference was due partly to pocket gophers whose earth moving activities reduce the density of vegetation and bury and kill individual Pen~ stemon plants. Laboratory feeding trials showed that gophers readily eat Penstemon, particularly the fleshy roots. An experiment involving the removal of 25-75% of the root tissue in 90 plants showed that root loss significantly reduced survivorship, suggesting that gopher herbivory might also kill plants. When gophers were experimentally excluded, plants growing in sparse vegetation exhibited significantly lower mortality rates than those growing in dense vegetation. Plants in the smallest size class exhibited reduced survivorship following a late spring burn; however, overall patterns of survivorship of plants in burned areas did not differ markedly from those in the unburned areas. A longitudenal analysis of plants with different reproductive histories revealed no survivorship cost to reproduction. Mortality rates decreased with increasing plant size. Small plants were more likely to be killed by fire and by being buried under gopher mounds. Differences in underground energy reserves of small and large plants can account for most of the survivorship patterns observed in this study. The study shows that within openings of the oak woodland, fire and gophers reduce the survival of individual Penstemon plants. Nevertheless, since both gophers and fire also serve to perpetuate suitable habitat in the woodland, Penstemon is ultimately dependent on both for its long term persistence in the landscape.

Conceptual Ecology and Invasion Biology: Reciprocal Approaches to Nature

Annals of the Entomological Society of America, 1981

The flight capacity of dispersing milkweed beetles, Tetraopes tetraopthalmus (Forster) (Cerambyci... more The flight capacity of dispersing milkweed beetles, Tetraopes tetraopthalmus (Forster) (Cerambycidae), was measured by using a still-air tethering technique and compared with the flight capacity of beetles randomly collected from source populations (milkweed patches). The mean flight duration of the dispersing group was 80 to 325% greater than that for any source population. These data attest to the validity of the tethered flight procedure. The flight capacity of insects is often measured as the flight duration of insects flown on tether in the labora

Bulletin of the Ecological Society of America

Background/Question/Methods Many forested areas that are part of the Mississippi River corridor i... more Background/Question/Methods Many forested areas that are part of the Mississippi River corridor in east-central Minnesota currently lack ground nesting passerines, although records document ground nesting passerines, particularly ovenbirds, in the same forests in the past. In order to determine if high predation rates may be responsible for the absence of these birds in some areas, we placed a quail egg and a clay egg in artificial ground nests in sites with and without ovenbirds in summer 2012 and 2013. The purpose of the clay egg was to reveal clues (e.g., bill, teeth, claw marks) as to the identity of egg predators. In addition, we also used several infrared trail cameras to identify nest predators. Nests were checked every other day for 14 days and two sets of artificial nests were created and tracked, the first set implemented during the first two weeks of June and the second set implemented during the last two weeks in June. Nest survival probability was calculated using the M...

Bulletin of the Ecological Society of America

1 The invasion of habitats by non-native plant and animal species is a global phe-nomenon with po... more 1 The invasion of habitats by non-native plant and animal species is a global phe-nomenon with potentially grave consequences for ecological, economic, and social systems. Unfortunately, to date, the study of invasions has been primarily anecdo-tal and resistant to generalization. 2 Here, we use insights from experiments and from long-term monitoring studies of vegetation to propose a new theory in which fluctuation in resource availability is identified as the key factor controlling invasibility, the susceptibility of an envir-onment to invasion by non-resident species. The theory is mechanistic and quanti-tative in nature leading to a variety of testable predictions. 3 We conclude that the elusive nature of the invasion process arises from the fact that it depends upon conditions of resource enrichment or release that have a vari-ety of causes but which occur only intermittently and, to result in invasion, must coincide with availability of invading propagules. Key-words: plant in...

Charles S. Elton and the dissociation of invasion ecology from the rest of ecology

Ecosphere, 2021

Due to decades of fire suppression, much of the Upper Midwest savanna habitat has converted to oa... more Due to decades of fire suppression, much of the Upper Midwest savanna habitat has converted to oak woodland. In efforts to restore oak savanna habitat, fire has been re‐introduced in many of these woodlands. A primary purpose of these burns is to kill the fire‐sensitive mesophytic tree species, which had established themselves during the decades of fire suppression, reduce the number of understory trees, and preserve the larger more widely spaced oaks. It is clear from ongoing efforts that restoring oak savannas will require frequent fires over decades, but frequent fires over the long term can also threaten the desirable oaks. Long‐term demographic studies at savanna restoration sites experiencing frequent fires are necessary to determine the extent to the frequent burns are supporting and/or confounding restoration goals. Results presented here are from a twenty‐five‐year demographic study of an Upper Midwest bur oak (Quercus macrocarpa) savanna/woodland experiencing frequent fire...

Science, 2000

's News Focus article about the restoration of North America's forests (28 Jan., p. 573) suggests... more 's News Focus article about the restoration of North America's forests (28 Jan., p. 573) suggests to me that it might be time to retire the word "restoration." There are at least three problems with the field of restoration ecology. First is the arbitrariness of determining which time period in the past should be the target of restoration efforts. In the United States, this has typically been assumed to be before settlement by Europeans. But why should that be the target any more than the time before the native Americans settled the region? Perhaps the most common environment in the past 15,000 years should be the target. In Minnesota, this would mean that much of the landscape would be restored to several hundred meters of ice. The second problem is that there is an implication of stasis with the word "restored." Not only do we try to replicate some past environment, but then we try to maintain it in that form through management. Yet nature is not static. The third problem is that true restoration is simply impossible. The climate is no longer the same, and keystone species are absent or new species are present that make it impossible to truly restore the habitat to any prior state. The goals of restoration ecology are certainly worthy ones and have captured the imagination of many of our students who have gone on in careers in the field. What seems to have become outdated is not the passion to better our environment, but the word "restoration" itself. Some students initially attracted to the field end up disenchanted as they come to realize that restoration ecology is at best a fiction and at worst motivated by a particular dominant cultural perspective. "Ecological enhancement" or "ecological enrichment" more accurately describes what we are really doing when we say we are "restoring" a site, and these terms avoid at least some of the assumptions and pretenses inherent in the word "restoration." As a formal discipline, perhaps restoration ecology should become a subdiscipline of landscape architecture and referred to as "ecological architecture." Of course, the goals and methods will still be arbitrary, developed by the various stakeholders, because nature itself provides no specific prescription for human intervention. But "ecological architecture" more aptly describes what we have been doing all along-conceiving and then trying to realize a new vision for a natural landscape.

Frontiers in Ecology and the Environment, 2004

The Society for Ecological Restoration's Science & Policy Working Group define ecological restora... more The Society for Ecological Restoration's Science & Policy Working Group define ecological restoration as the process of assisting the recovery of damaged, degraded, or destroyed ecosys? tems (SER 2002). While ecological restoration involves restoring ecosystems at specific project sites, restoration ecology is the science on which the practice is based, and should ideally provide clear concepts, models, methodologies, and tools to support it. Restoration ecology is still an emerging science, with its roots in practical restoration projects around the world. Research generally focuses on improving the conceptual, technical, and socioeconomic bases for conducting effective ecological restoration. In recent years, there has been a move away from site-and situation-specific studies of particular restoration projects to a broader consideration of the conceptual basis for restoration ecology and the publication of synthetic treatments of the subject (Hobbs and Norton 1996; Whisenant 1999; Hobbs and Harris 2001; Perrow and Davy 2002; Temperton et al. in press). To restore an ecosystem, we need to understand how it worked before it was modified or degraded, and then use this understanding to reassemble it and reinstate essential processes. There is an increasing recognition that ecosystem dynamics can be complex, non-linear, and often unpredictable. The importance of broadscale processes and interactions between adjoining ecosystems adds further complexity, since impacts in one place may be the result of events or management decisions elsewhere. This makes it difficult to correctly diagnose the problems leading to ecosystem degrada? tion or preventing recovery, and to initiate effective corrective or restorative management. The type of intervention required in restoration depends heavily on the type and extent of damage to the ecosystem. In some cases, relatively small changes in the management or manipulation of the species composition are required, as in the removal of harmful invasive species or the replacement of missing species. In other cases, a substantial alteration of the physical cases, and at what cost, is required. In most cases, there will be a range of options that vary in expected outcome and relative cost, and there needs to be a clear ? The Ecological Society of America www.frontierfcinecoiogy.org This content downloaded on Fri, 4 Jan 2013 14:13:00 PM All use subject to JSTOR Terms and Conditions 1996). ? References Bradshaw AD. 1983. The reconstruction of ecosystems. J Appl Ecol 20: 1-17. www.frontiersinecology.org ? The Ecological Society of America This content downloaded on Fri, 4 Jan 2013 14:13:00 PM All use subject to JSTOR Terms and Conditions Forum Restoration ecology: the challenge of social values and expectations Bradshaw AD and Chadwick MJ. 1980. The restoration of land. Oxford, UK: Blackwell Publishing.

Mètode Revista de difusió de la investigació, 2018

In the 1980s, three sub-disciplines of ecology emerged – restoration ecology, conservation biolog... more In the 1980s, three sub-disciplines of ecology emerged – restoration ecology, conservation biology, and invasion biology – and all three embraced the nativism paradigm. By the early 2000s, historians, sociologists, and philosophers interested in the development of science began to examine the growing field of invasion biology and usually were critical of it. In the past few years, a new perspective has been taking hold in the field of ecology. Referred to as ecological novelty it emphasizes that many factors are producing ecologically novel environments. A much more simply descriptive concept, it is currently competing with the nativism paradigm to define nature. Whether the nativism or ecological novelty paradigm emerges as the dominant perspective going forward will determine how nature and biodiversity are managed.

BioScience, 2004

Books foot-tall spruce to see life from a treetop perspective. Swallows migrated to the moon, ass... more Books foot-tall spruce to see life from a treetop perspective. Swallows migrated to the moon, asserted naturalist John Morton in the late 18th century. Heinrich's splendid book gives us a more informed view of animals' adaptations, in this case, the adaptations that enable survival in winter. It is the rare book that teaches us to see more clearly even as it delights us. Winter World will impel you to take a walk in the winter woods.

Oecologia, 1981

The reproductive success and energy budgets of single and multiflowered plants of Trillium erectu... more The reproductive success and energy budgets of single and multiflowered plants of Trillium erectum L. (Liliaceae) were assessed over a period of 4 years. Plants with more than one flower were found to attract more pollinators, to be less vulnerable to predation by Tortricid moths, and to produce more seeds than single flowered plants. Despite the reproductive superiority exhibited by multiflowered plants, most plants (85%) in the population studied were single flowered. It is shown that even though the insect interactions make it advantageous to produce more than one flower, most plants lack the energy to do so. The optimality approach which has guided previous studies of this kind is criticzied.

Oecologia, 1991

The effects of fire and pocket gophers, Geomys bursarius, on the survivorship of Penstemon 9randi... more The effects of fire and pocket gophers, Geomys bursarius, on the survivorship of Penstemon 9randiflorus growing in an oak woodland in Minnesota were studied from 1986 to 1990. Plants growing in sparse vegetation experienced mortality rates twice that of plants growing in dense vegetation. This difference was due partly to pocket gophers whose earth moving activities reduce the density of vegetation and bury and kill individual Pen~ stemon plants. Laboratory feeding trials showed that gophers readily eat Penstemon, particularly the fleshy roots. An experiment involving the removal of 25-75% of the root tissue in 90 plants showed that root loss significantly reduced survivorship, suggesting that gopher herbivory might also kill plants. When gophers were experimentally excluded, plants growing in sparse vegetation exhibited significantly lower mortality rates than those growing in dense vegetation. Plants in the smallest size class exhibited reduced survivorship following a late spring burn; however, overall patterns of survivorship of plants in burned areas did not differ markedly from those in the unburned areas. A longitudenal analysis of plants with different reproductive histories revealed no survivorship cost to reproduction. Mortality rates decreased with increasing plant size. Small plants were more likely to be killed by fire and by being buried under gopher mounds. Differences in underground energy reserves of small and large plants can account for most of the survivorship patterns observed in this study. The study shows that within openings of the oak woodland, fire and gophers reduce the survival of individual Penstemon plants. Nevertheless, since both gophers and fire also serve to perpetuate suitable habitat in the woodland, Penstemon is ultimately dependent on both for its long term persistence in the landscape.

Conceptual Ecology and Invasion Biology: Reciprocal Approaches to Nature

Annals of the Entomological Society of America, 1981

The flight capacity of dispersing milkweed beetles, Tetraopes tetraopthalmus (Forster) (Cerambyci... more The flight capacity of dispersing milkweed beetles, Tetraopes tetraopthalmus (Forster) (Cerambycidae), was measured by using a still-air tethering technique and compared with the flight capacity of beetles randomly collected from source populations (milkweed patches). The mean flight duration of the dispersing group was 80 to 325% greater than that for any source population. These data attest to the validity of the tethered flight procedure. The flight capacity of insects is often measured as the flight duration of insects flown on tether in the labora

Bulletin of the Ecological Society of America

Background/Question/Methods Many forested areas that are part of the Mississippi River corridor i... more Background/Question/Methods Many forested areas that are part of the Mississippi River corridor in east-central Minnesota currently lack ground nesting passerines, although records document ground nesting passerines, particularly ovenbirds, in the same forests in the past. In order to determine if high predation rates may be responsible for the absence of these birds in some areas, we placed a quail egg and a clay egg in artificial ground nests in sites with and without ovenbirds in summer 2012 and 2013. The purpose of the clay egg was to reveal clues (e.g., bill, teeth, claw marks) as to the identity of egg predators. In addition, we also used several infrared trail cameras to identify nest predators. Nests were checked every other day for 14 days and two sets of artificial nests were created and tracked, the first set implemented during the first two weeks of June and the second set implemented during the last two weeks in June. Nest survival probability was calculated using the M...

Bulletin of the Ecological Society of America