Ingrid M Parker

• PhD
• Professor (Full) at University of California, Santa Cruz

Global environmental change will affect non-native plant invasions, with profound potential impacts on native plant populations, communities and ecosystems. In this context, we review plant functional traits, particularly those that drive invader abundance (invasiveness) and impacts, as well as the integration of these traits across multiple ecolog...

Plants interact with numerous enemies and mutualists simultaneously and sequentially. Such multispecies interactions can give rise to trait-mediated indirect effects that are likely to be common in nature but which are also inherently difficult to predict. Understanding multispecies interactions is also important in the use of biological control ag...

An important question in the study of biological invasions is the degree to which successful invasion can be explained by release from control by natural enemies. Natural enemies dominate explanations of two alternate phenomena: that most introduced plants fail to establish viable populations (biotic resistance hypothesis) and that some introduced...

The ability to reproduce via multiple strategies is crucial for the invasion success of alien plant species. Here, we use Carpobrotus taxa (species and hybrids) to explore how trade-offs between and within these strategies may influence plant invasion dynamics. Native to South Africa, Carpobrotus plants are globally prominent in coastal ecosystems,...

Large‐scale restoration projects are an exciting and often untapped opportunity to use an experimental approach to inform ecosystem management and test ecological theory. In our $10M tidal marsh restoration project, we installed over 17,000 high marsh plants to increase cover and diversity, using these plantings in a large‐scale experiment to test...

Invasive plants along transportation corridors can significantly threaten ecosystems and biodiversity if they spread beyond anthropogenic environments. Rapid evolution may increase the ability of invading plant populations to establish in resident plant communities over time, posing a challenge to invasion risk assessment. We tested for adaptive di...

Range expansions, whether they are biological invasions or climate change-mediated range shifts, may have profound ecological and evolutionary consequences for plant-soil interactions. Range-expanding plants encounter soil biota with which they have a limited coevolutionary history, especially when introduced to a new continent. Past studies have f...

Invasions by multiple non‐native plant species are common, but management programs often prioritize control of individual species that are expected to have the highest impacts. Multi‐species invasions could have larger or smaller impacts than single‐species invasions depending on how multiple co‐occurring invaders interact to alter their abundance...

Dittrichia graveolens (L.) Greuter, or stinkwort, is a weedy annual plant within the family Asteraceae. The species is recognized for the rapid expansion of both its native and introduced ranges: in Europe, it has expanded its native distribution northward from the Mediterranean basin by nearly 7 degrees latitude since the mid-20th century, while i...

Invasive C4 grasses can inhibit the natural regeneration of secondary forest in tropical landscapes after the cessation of intensive use for grazing and agriculture. In Panama, invasive Saccharum spontaneum forms dense stands that require active management to re-establish forest successional processes. In this region, restoration strategies typical...

Understanding the symbiosis between plants and pathogenic microbes is at the core of effective disease management for crops and managed forests. At the same time, plant–pathogen interactions comprise a wonderfully diverse set of ecological relationships that are powerful and yet so commonplace that they often go unnoticed. Ecologists and evolutiona...

Plants are primary producers, converting atmospheric carbon dioxide into sugars through photosynthesis. Plant pathogens take advantage of this energy source, and because the plant immune system is not comprised of specialized cells or organs, every plant cell must defend itself. The plant vascular system moves water and mineral nutrients through xy...

Plant pathogens affect their hosts in diverse ways. Some deprive the host of carbon by parasitizing it or by reducing photosynthetic tissue, and some restrict access to water by disrupting the vascular system; either can slow the growth of the plant and reduce host fecundity. Other pathogens directly kill parts or all of the plant, and still other...

Fungi are the most abundant and diverse of plant pathogens. Filamentous fungi grow as long tubes called hyphae that form mycelial networks. They obtain nutrition as osmotrophic heterotrophs, secreting enzymes into the substrate that surrounds them, then absorbing simpler compounds rich in carbon and nutrients. Fungi reproduce asexually and sexually...

Evolutionary biology includes microevolution, which incorporates genetics into the study of traits, and macroevolution, which focuses on patterns of traits across the history of life. Evolution proceeds via both random changes in allele frequency through genetic drift and non-random changes through natural selection. Genetic drift is important in s...

Plants lack antibody-based immune systems, but they do have a robust system of defenses against pathogens. Constitutive defenses are a broad array of constitutively-produced physical structures and chemical compounds that protect most plants from infection by most pathogens. The three major groups of plant chemical defenses are phenolics, terpenoid...

Viruses are non-cellular pathogens. Plant viruses are obligate parasites of plant host cells that rely on their host for transcription and replication. Viruses disrupt the growth of plants by dominating host resources for transcription and translation, and sometimes by manipulating host cellular processes. There are six groups of plant viruses, cla...

Population ecology concerns the structure and numerical dynamics of populations; it uses mathematical models to understand patterns in groups of organisms and their interactions. In plant populations, the spread of disease through time generally falls into two types: monocyclic and polycyclic. For monocyclic diseases, plants are infected from prima...

Oomycetes are in the Stramenopiles group of protists and many are aggressive plant pathogens. Oomycetes grow as coenocytic hyphae creating mycelial networks. They can reproduce through long-lasting sexual oospores or asexual chlamydospores. Sometimes called water molds, when provided with abundant moisture they can produce sporangia that release mo...

Plant-associated bacteria are heterotrophic prokaryotes, forming a diversity of types of symbioses with plants. Bacteria reproduce through binary fission, and they achieve large population sizes very rapidly through exponential growth. Bacteria often grow in biofilms on plants or in soil, incorporating extracellular polysaccharides as structure. Qu...

The assemblage of microbes that inhabit the plant as symbionts comprise the plant microbiome. The activities of plant roots have a dramatic effect on the density and composition of bacteria and fungi growing around them, known as the rhizosphere effect. Plant-microbe and microbe-microbe interactions in the rhizosphere have large impacts on plant he...

Accelerating patterns of land-use change, air pollution, global trade, and climate change all contribute to changes in plant-pathogen interactions and the emergence of novel infectious plant diseases. Land conversion to agriculture has led to new encounters between crops and local pathogens, leading to the emergence of novel diseases through spillo...

Management of plant diseases relies on two general strategies: avoidance and control. Avoidance tactics involve evasion of pathogens by not planting susceptible crops in areas where virulent pathogens are present, and exclusion of pathogens through phytosanitary practices. Control tactics rely on planting crop cultivars with genetic and physiologic...

Plant disease ecologists rely on a wide array of technical skills to diagnose and study plant disease. Disease intensity can be measured as the prevalence of disease across a host population or the severity of disease in individual plants. Sampling plans must consider both precision and accuracy. Plant diseases are diagnosed through the combination...

Community ecology is the study of interactions among species and the resulting diversity, composition, and structure of communities of organisms. Diversity is comprised of the number, types and relative abundances of species in the community. Most communities have a few common species and many rare ones. Within-community diversity is called alpha d...

Spatial ecology is the study of spatial structure in populations and communities and the processes that create that structure. Disease spreads through plant populations when propagules of pathogens disperse from one plant to another. Propagules often disperse passively, moving via currents of air or water. However, some motile pathogens disperse ac...

Two groups of larger organisms cause disease on plants: plants and nematodes. Parasitic plants may be holoparasites that depend on their host plants for water, nutrients, and sugars, while hemiparasites tap into xylem and exploit their hosts for water only. Mistletoes, dodder, and witchweeds are well-known examples. Parasitic plants evolved indepen...

Plant disease is the outcome of antagonistic symbiotic interactions between pathogenic microorganisms and susceptible hosts, contingent on environmental conditions that are favorable for infection and symptom development. Plant-microbe symbioses can range from mutualistic to parasitic. The ecological outcomes of plant-microbe interactions are the p...

Understanding the symbiosis between plants and pathogenic microbes is at the core of effective disease management for crops and managed forests. At the same time, plant–pathogen interactions comprise a wonderfully diverse set of ecological relationships that are powerful and yet so commonplace that they often go unnoticed. Ecologists and evolutiona...

Understanding the symbiosis between plants and pathogenic microbes is at the core of effective disease management for crops and managed forests. At the same time, plant–pathogen interactions comprise a wonderfully diverse set of ecological relationships that are powerful and yet so commonplace that they often go unnoticed. Ecologists and evolutiona...

Understanding the symbiosis between plants and pathogenic microbes is at the core of effective disease management for crops and managed forests. At the same time, plant–pathogen interactions comprise a wonderfully diverse set of ecological relationships that are powerful and yet so commonplace that they often go unnoticed. Ecologists and evolutiona...

Understanding the symbiosis between plants and pathogenic microbes is at the core of effective disease management for crops and managed forests. At the same time, plant–pathogen interactions comprise a wonderfully diverse set of ecological relationships that are powerful and yet so commonplace that they often go unnoticed. Ecologists and evolutiona...

A major aim in invasion ecology is to understand the role of exotic species in plant communities. Whereas most studies have explored the traits of exotic species in the context of the introduced community, functional comparisons of entire assemblages of species in their native and introduced communities have rarely been analysed. Taking advantage o...

Plant pathogens are often hypothesized to promote species coexistence by generating conspecific negative density dependence (CNDD). However, the relative importance of fungal versus oomycete pathogens in maintaining plant species coexistence and community composition remains unresolved, despite their recognized effects on plant performance. Here, w...

The phylogenetic distance between species often predicts differences in ecologically important traits. The phylogenetic diversity and structure of biological communities can inform our understanding of the processes that shape those communities, and there is a well-developed framework for comparing phylogenetic structures of communities. However, p...

The Stress Gradient Hypothesis (SGH) predicts facilitation will become more important than competition where abiotic stress is high, and the framework successfully predicts positive interactions between species in many systems. Fewer studies have focused on intraspecific facilitation, and to our knowledge none examine intraspecific interactions in...

Aim Although ecological niche models have been instrumental in understanding the widespread species distribution shifts under global change, rapid niche shifts limit model transferability to novel locations or time periods. Niche shifts during range expansion have been studied extensively in invasive species, but may also occur in native population...

Racial and ethnic discrimination persist in science, technology, engineering and mathematics fields, including ecology, evolution and conservation biology (EECB) and related disciplines. Marginalization and oppression as a result of institutional and structural racism continue to create barriers to inclusion for Black people, Indigenous people and...

Aim Although ecological niche models have been instrumental in understanding the widespread species distribution shifts under global change, rapid niche shifts limit model transferability to novel locations or time periods. Niche shifts during range expansion have been studied extensively in invasive species, but may also occur in native population...

Political and economic initiatives intended to increase energy production while reducing carbon emissions are driving demand for solar energy. Consequently, desert regions are now targeted for development of large‐scale photovoltaic solar energy facilities. Where vegetation communities are left intact or restored within facilities, ground‐mounted i...

Background and aims Plant-soil feedbacks may determine the long-term success of introduced species. Here we examined plant-soil feedbacks of a globally invasive shrub, Cytisus scoparius (hereafter Cytisus), which associates with multiple guilds of microbial mutualists and dominates harvested Douglas-fir forests in the Pacific Northwest. Methods We...

Seed bank survival underpins plant population persistence but studies on seed bank trait-environment interactions are few. Changes in environmental conditions relevant to seed banks occur in desert ecosystems owing to solar energy development. We developed a conceptual model of seed bank survival to complement methodologies using in-situ seed bank...

Invasion ecology has grown to include scientists with diverse skill sets who focus on a range of taxa and biomes. These researchers have the capacity to contribute to practical management solutions while also answering fundamental biological questions; however, scientific endeavors often fail to meet the perceived needs of practitioners involved in...

Seed bank survival underpins plant population persistence but studies on seed bank trait-environment interactions are few. Changes in environmental conditions relevant to seed banks occur in desert ecosystems owing to solar energy development. We developed a conceptual model of seed bank survival to complement methodologies using in-situ seed bank...

Predicting how communities re-arrange in response to changes in species composition remains a key challenge in ecology. Migratory species, which enter and leave communities across latitudinal gradients, offer us a unique opportunity to evaluate community- and species-level responses to a shift in community composition. We focused on a migratory hum...

The introduction of exotic species to new regions offers opportunities to test fundamental questions in ecology, such as the context-dependency of community structure and assembly. Annual grasslands provide a model system of a major unidirectional introduction of plant species from Europe to North America. We compared the community structure of gra...

Solar energy development is a significant driver of land-use change worldwide, and desert ecosystems are particularly well suited to energy production because of their high insolation rates. Deserts are also characterized by uncertain rainfall, high species endemism, and distinct landforms that vary in geo-physical properties. Weather and physical...

We conducted a large-scale, multiple-year study in harvested areas of Douglas-fir forests in western Washington, examining the effectiveness of control methods on the widespread invasive shrub Scotch broom [ Cytisus scoparius (L.) Link]. We tested both chemical and physical control methods, using three different approaches that are management-relev...

The relationship between plant diversity and productivity and the mechanisms underpinning that relationship remain poorly resolved in species-rich forests. We combined extensive field observations and experimental manipulations in a subtropical forest to test how species richness (SR) and phylogenetic diversity (PD) interact with putative root-asso...

Non-native tree (NNT) species have been transported worldwide to create or enhance services that are fundamental for human well-being, such as timber provision, erosion control or ornamental value; yet NNTs can also produce undesired effects, such as fire proneness or pollen allergenicity. Despite the variety of effects that NNTs have on multiple e...

Reforestation is challenging when timber harvested areas have been degraded, invaded by nonnative species, or are of marginal suitability to begin with. Conifers form mutualistic partnerships with ectomycorrhizal fungi (EMF) to obtain greater access to soil resources, and these partnerships may be especially important in degraded areas. However, ti...

Plant pathogens reduce the performance of their hosts and therefore may contribute to ecological mechanisms of coexistence. In Chesson’s framework, pathogens contribute to stabilizing mechanisms when they intensify negative intraspecific interactions, such as density‐dependent disease. Additionally, pathogens contribute to equalizing mechanisms whe...

Erect veldtgrass ( Ehrharta erecta Lam.) is an invasive grass actively spreading in California that is capable of invading multiple habitats. Our objective is to contribute to a better understanding of the ecology, impacts, and potential for control of E. erecta in order to guide management practices. In a mixed-evergreen forest in Santa Cruz Count...

Social factors play a critical role in almost every conservation problem. There is a pressing need for conservation researchers and practitioners to understand both the ecological and human dimensions of their systems in order for projects to be successful. At the same time, many conservation professionals come from a natural science background wit...

An increasingly recognized impact of plant invaders is the disruption of positive interactions between native plants and their belowground mutualistic mycorrhizal fungi. We reviewed 112 studies from 61 publications that report invader impacts on mycorrhizal fungi. We describe emerging patterns on the frequency of negative, neutral and positive inva...

Invasive plants often occupy large ranges in the introduced region and consequently, local population dynamics vary in ways that affect the potential for biological control. We used matrix models to describe how density and population growth rate of Centaurea solstitialis varies in time and space. Matrix models were parameterized with data collecte...

Impacts of invasive species may change in magnitude and even direction with invasion age. Impacts could increase as the population increases, individuals grow in size and ecological changes accumulate. We used a chronosequence approach to characterize the development of soil impacts over time following the invasion of Cytisus scoparius , a widespre...

Premise of the study: Self incompatibility (SI) in rare plants presents a unique challenge-SI protects plants from inbreeding depression, but requires a sufficient number of mates and xenogamous pollination. Does SI persist in an endangered polyploid? Is pollinator visitation sufficient to ensure reproductive success? Is there evidence of inbreedi...

Through competition for pollinators, invasive plants may suppress native flora. Community-level studies provide an integrative assessment of invasion impacts and insights into factors that influence the vulnerability of different native species. We investigated effects of the non-native herb Lythrum salicaria on pollination of native species in 14...

Species introductions are a dominant component of biodiversity change but are not explicitly included in most discussions of biodiversity-disease relationships. This is a major oversight given the multitude of effects that introduced species have on both parasitism and native hosts. Drawing on both animal and plant systems, we review the competing...

An explicit phylogenetic perspective provides useful tools for phytopathology and plant disease ecology because the traits of both plants and microbes are shaped by their evolutionary histories. We present brief primers on phylogenetic signal and the analytical tools of phylogenetic ecology. We review the literature and find abundant evidence of ph...

Models are simplified representations of more complex systems that help scientists structure the knowledge they acquire. As such, they are ubiquitous and invaluable in scientific research and communication. Because science education strives to make classroom activities more closely reflect science in practice, models have become integral teaching a...

Aims To assess the impacts of Ailanthus altissima and Robinia pseudoacacia on the whole litterfall process and on soil properties of riparian ecosystems of Central Spain by comparing invaded and non-invaded forests. Methods We selected 3–4 plots of four different types of forests: invaded by A. altissima or R. pseudoacacia, or dominated by the nati...

Vast effort and resources are spent to control invasive plants. Often with the assumption that once these resources are spent and the invader is successfully removed, the impact of that species on the community is also eliminated. However, invasive species may change the environment in ways that persist, as legacy effects, after the species itself...

Pathogens play an important part in shaping the structure and dynamics of natural communities, because species are not affected by them equally. A shared goal of ecology and epidemiology is to predict when a species is most vulnerable to disease. A leading hypothesis asserts that the impact of disease should increase with host abundance, producing...

Summary Schedules of survival, growth and reproduction are key life-history traits. Data on how these traits vary among species and populations are fundamental to our understanding of the ecological conditions that have shaped plant evolution. Because these demographic schedules determine population growth or decline, such data help us understand h...

An age-old conflict around a seemingly simple question has resurfaced: why do we conserve nature? Contention around this issue has come and gone many times, but in the past several years we believe that it has reappeared as an increasingly acrimonious debate between, in essence, those who argue that nature should be protected for its own sake (intr...

Background/Question/Methods Islands and island-like habitats are biodiversity hotspots. The insular nature of these environments limits gene flow and facilitates local adaptation. The Zayante sandhills of Santa Cruz County, California, contain many plants and animals restricted to these exceptionally xeric soils surrounded by mesic forests. Erysi...

Background/Question/Methods Rare host species are expected to suffer less damage from pathogens and pests than common hosts. This rare-species advantage is a key feature of hypotheses that explain how pathogens can help maintain diversity (e.g., Janzen-Connell hypothesis) or regulate invasions (e.g., Escape from Natural Enemies hypothesis). Howev...

Background/Question/Methods Ehrharta erecta is a highly invasive perennial grass actively spreading in forest understory habitats across coastal California. Despite the attention placed on this species as a wildland weed, there is little published information on its impacts or control. We quantified the impacts of E. erecta on native plant physio...

Background/Question/Methods Invasive plants compete with native plants for pollination when pollinators preferentially visit the flowers of the invader. Over a broader scale, invaders may facilitate native plant pollination by attracting visitors to the invaded site or by increasing population sizes of pollinators at the site. Reviews of studies...

Background/Question/Methods It is typically assumed that once an invasive species is successfully removed, the impact of that species on the community is also eliminated. However, invasive species may change the environment in ways that persist, as legacy effects, long after the species itself is gone. To evaluate the persistence of soil legacy ef...

Establishing new populations is essential for preventing the extinction of critically endangered plant species. However, defining the range of environmental conditions suitable for the most severely endangered species is challenging, since few wild populations remain for study. Experimental reintroductions of these species can achieve multiple cons...

To identify the geographic origin of nodule bacteria associated with invasion of the European legume Cytisus scoparius in the United States, isolates from 15 sites in six states were compared to >200 Bradyrhizobium strains from indigenous legumes in the U.S., Mexico, Europe (six countries), Morocco and Australia. Portions of five housekeeping loci...

Species in the early stages of domestication, in which wild and cultivated forms co-occur, provide important opportunities to develop and test hypotheses about the origins of crop species. Chrysophyllum cainito (Sapotaceae), the star apple or caimito, is a semidomesticated tree widely cultivated for its edible fruits; it is known to be native to th...

• Premise of the study: We developed microsatellite primers for the tropical tree Chrysophyllum cainito (Sapotaceae) to determine the native range of the species, investigate the origin of cultivated populations, and examine the partitioning of genetic diversity in wild and cultivated populations. • Methods and Results: We developed 10 polymorphic...

Background/Question/Methods Even after the removal of the invasive shrub Cytisus scoparius, standard reforestation efforts in previously invaded areas often fail. In our previous work, we found that soils invaded by Cytisus harbored fewer ectomycorrhizal fungi than uninvaded forest soils, and that growth of Douglas-fir seedlings was linked to the...

Background and aim: Exotic plant species can alter the nitrogen cycle in invaded ecosystems. We assess the differences in nitrogen use strategies and litter production and dynamics among three native riparian trees (Fraxinus angustifolia, Populus alba and Ulmus minor) and three co-occurring exotics (Ailanthus altissima, Robinia pseudoacacia and Ulm...

Herbivores, seed predators, and pollinators can exert strong impacts on their host plants. They can also affect the strength of each other's impact by modifying traits in their shared host, producing super- or sub-additive outcomes. This phenomenon is especially relevant to biological control of invasive plants because most invaders are attacked by...

Forest restoration uses active management to re-establish natural forest habitat after disturbance. However, competition from early successional species, often aggressively invasive exotic plant species, can inhibit tree establishment and forest regeneration. Ideally, restoration ecologists can plant native tree species that not only establish and...

Invasive species may leave behind legacies that persist even after removal, inhibiting subsequent restoration efforts. We examined the soil legacy of Cytisus scoparius, a nitrogen-fixing, putatively allelopathic shrub invading the western US. We tested the hypothesis that allelopathy plays a critical role in the depressive effect of Cytisus on the...

Background/Question/Methods Invasive species offer excellent opportunities to test evolutionary hypothesis and to study basic processes in population biology. In particular, invasive species represent attractive study models to test the predictions of life history theory, since the selective pressures in the native and introduced habitats can be...

Background/Question/Methods Even after the removal of the invasive shrub Cytisus scoparius, standard reforestation efforts in previously invaded areas often fail. In our previous work, we have found that soils invaded by Cytisus harbor less ectomycorrhizal fungi, and that growth of Douglas-fir seedlings is linked to the abundance of these fungi....

Background/Question/Methods Studying the differences in the nitrogen use strategy between native and exotic plant species can help to explain invasion success and to predict potential impacts on the nitrogen cycle of invaded communities. Plants adapted to nitrogen-rich ecosystems usually show leaf traits related to non-conservative nitrogen use s...

Background/Question/Methods Forest restoration is the re-introduction of native species to naturally or anthropogenically disturbed areas to re-establish the natural habitat. Early successional species, especially invasive exotic species, can inhibit or delay succession to the desired restoration endpoint. Restoration of areas occupied by undesir...

Premise of the study: Understanding patterns and processes associated with domestication has implications for crop development and agricultural biodiversity conservation. Semi-domesticated crops provide excellent opportunities to examine the interplay of natural and anthropogenic influences on plant evolution. The domestication process has not bee...