Research Interests

We are ecologists and evolutionary biologists who aim to better understand how the natural world works.  Curiosity and unsolved real-world problems motivate us to characterize patterns in nature and to advance or evaluate scientific hypotheses for the consilient processes (i.e., mutually compatible mechanisms) that cause, create, maintain, or modify those patterns.  In these evidence-based pursuits, our attention is especially drawn toward the hierarchical levels of biological organization that range from organisms – through populations and communities – to ecosystems, including the global biosphere.  We primarily study phenomena that intrigue us as naturalists and natural historians, or that concern us as conservation biologists, environmentalists, and engaged global citizens who strive for conservation of biodiversity, social and environmental justice, and planet-wide sustainability.

 

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Groundcover Diversity & Dynamics in Longleaf Pine Ecosystems
of the Subtropical Southeastern United States of America

Remnant and restored longleaf pine (Pinus palustris [Pinaceae]) ecosystems (savannas, flatwoods, sandhills, etc.) of the southeastern United States often support extreme levels of groundcover – mostly herbaceous – biodiversity.  We have contributed toward the overall mechanistic understanding of these extraordinary communities through observations and experiments on private and public lands in Florida (e.g., Eglin Air Force Base) and Louisiana (e.g., Camp Whispering Pines Girl Scout Camp and two of The Nature Conservancy's protected areas:  Abita Creek Flatwoods Preserve & Lake Ramsay Preserve).  To facilitate broader geographic comparisons, Bret Elderd, Jennie Kluse, and I shared our Lake Ramsay observational dataset – cover values per species for thirty 1-m² quadrats – with the globally distributed grassland project NutNet (our NutNet site name = "TNC Lake Ramsay Preserve"; our NutNet site code = "ramsay.us").

Our basic-science research on community assembly helps contextualize and quantify the roles of dispersal limitation, frequent fire, and species interactions in the high-diversity groundcover (e.g., Gagnon et al. 2012; Harms et al. 2017; Myers & Harms 2009, 2011).  In addition, we found that the few bunchgrass species that physically dominate the groundcover – as a guild of foundation species – tend to be over-dispersed (Hovanes et al. 2018).  This spatial-patterning phenomeonon is a key to understanding these high-diversity communities.  Specifically, since the dominant bunchgrasses do not form continuous lawns, diverse smaller-stature forbs and grasses establish and persist in the interstices among the dominant-grass tussocks, yet with limited opportunities to outcompete one another.

Our fire-ecology research implicates soil heating as a principal driver of groundcover assembly (Gagnon et al. 2015).  In addition, extreme flammability of above-ground organs in many plants from fire-prone ecosystems may provide adaptive protection to underground regenerative tissue from lethal heating during fires (Gagnon et al. 2010).  We proposed through our pyrogenicity-as-protection adaptive hypothesis (a.k.a. save-thyself hypothesis) that highly flammable plants burn quickly, which reduces the duration of soil heating, by which plants protect their underground perennating organs or offspring as seeds in the soil seedbank.  Our idea is a mutually compatible alternative to the kill-thy-neighbor hypothesis (Bond & Midgley, 1995, Oikos).  In other words – one, or the other, or both – could favor the evolution of highly flammable plants.

We also capitalize on opportunities to apply and translate our science toward conservation and restoration in longleaf pine ecosystems, especially through educational and management-based outreach.  For example, see my essays in The Longleaf Alliance's quarterly magazine, The Longleaf Leader (Harms 2019, re the ecological importance of native bunchgrasses; Harms 2023, re the old-growth concept applied to southeastern U.S. grasslands).  Also see our workshop report (Harms et al. 2015) with recommendations to the Partnership Council of America's Longleaf Restoration Initiative.

A concept that emerged from our work in longleaf ecosystems and which we think has broad global applicability is the idea that Species of Unusual Effect (SUEs) deserve special attention in conservation and restoration (Harms 2022).  SUEs comprise keystone species, ecosystem engineers, foundation species (such as little bluestem and wiregrass in longleaf pine savannas), and any other species that play outsized roles in either community assembly or ecosystem functions (e.g., productivity, nutrient cycling, etc.).

We thank Eglin Air Force Base (specifically Jackson Guard), the Girl Scouts of America, the National Science Foundation (grants DEB #0516175, DEB #114408), and The Nature Conservancy for supporting our projects.

 

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Rainforest Diversity & Dynamics in Queensland, Australia

During a more than half-century-long, highly productive career, our inspirational mentor and friend, Joe Connell (1923-2020; see Sousa et al. 2021), established long-term research projects in Australian rainforests (e.g., Connell et al. 2005) and on the Great Barrier Reef (e.g., Connell et al. 2004), among others.  Joe initiated his forest dynamics project at sites in tropical (Davies Creek & Dinden National Parks) and subtropical (Lamington National Park) Queensland, Australia in 1963.  Pete Green (La Trobe University, Australia) inherited and currently oversees the rainforests project.  In 2013, we conducted the 50^th anniversary census of the trees in Connell's plots (Harms & Green 2014); in 2023, we conducted the 60^th anniversary census (see my third place winning entry entitled "Rosa's Tree Hug" – taken during the census – on the website for the 2024 joint photo contest of the Association for Tropical Biology & Conservation and Society for Tropical Ecology). 

Using the Davies Creek (Queensland Wet Tropics) demographic data, we found empirical support for the long-standing idea in forest ecology that early-stage (e.g., seed and seedling) dynamics are especially consequential to forest composition and diversity (Green, Harms & Connell 2014).  These observations motivated us to develop conceptual models and mechanistic hypotheses concerning disproportionate non-random mortality among life-cycle stages in all types of communities (Green & Harms 2018).

In a first step toward better understanding the microbial influence on recruitment at Davies Creek, Jen Wood selectively sampled microbial assemblages in Connell's plot, and found compositional structure associated with non-random, diversifying seedling dynamics (Wood et al. 2020).

 

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Global Patterns of Neighborhood-Dependent Demographic Performance:  Influences of Neighbor Density, Distance & Phylogenetic Relatedness on Individual Trees & Lianas

Stemming from their stay-at-home lifestyles, plants tend to interact primarily with their near neighbors.  Accordingly, neighborhood interactions have the potential to shape community assembly (e.g., maintain diversity, organize patterns of alpha- and beta-diversity, etc.).  Our analyses of spatially detailed demographic records – especially for woody species in mapped forests – clearly indicate that non-random, neighborhood-scale, inter-individual interactions influence individual-level performance (growth, mortality, recruitment) – often in ways that could foster coexistence, as well as contribute toward the origins and maintenance of biodiversity. 

Among other patterns, we have found: 

(1) Negative conspecific density-dependent seed-to-seedling transitions among common species of trees and lianas in the Center for Tropical Forest Science (CTFS – a research branch of the Smithsonian Tropical Research Institute [STRI]; now ForestGEO) 50-ha Hubbell-Foster Forest Dynamics Plot (FDP) on Barro Colorado Island (BCI), Republic of Panama.  This pattern is consistent with the Janzen-Connell hypothesis for the maintenance of diversity in high-diversity plant communities (Harms et al. 2000).

(2) Density- and distance-dependent survival of seedlings and small saplings of a common canopy tree species on BCI (Gilbert et al. 2001); this pattern is also consistent with the Janzen-Connell hypothesis.

(3) Between-seedling distances too large for competition among conspecific seedlings to play a substantial role in early-stage, non-random seedling mortality at Cocha Cashu Biological Station, Peru (Paine et al. 2008).

(4) Reduced survival among established trees in conspecific-rich neighborhoods (with relatively consistent patterns among 5 CTFS FDPs in Asia and 2 in the Neotropics; Wills et al. 2006).

(5) Neighborhood influences on individual performance of saplings and established trees that generally – albeit idiosyncratically – taper off with phylogenetic distance separating the focal stem from its neighbors (Wills et al. 2016; Wills et al. 2021), based on our novel Equal-Area Annulus (EAA) point-pattern statistical method, which employs a stems'-traits-swapping randomization or null model, and which we have applied to several CTFS FDPs.

Several other research groups are improving our understanding of these neighborhood spatiotemporal phenomena with detailed work on the mechanisms (e.g., fungal pathogen infection, herbivory, vertebrate seed predation) that cause the patterns.  (See also the previous section on this webpage regarding Jen Wood's work on microbial assemblages associated with the early life-cycle stage distance- and density-dependence that we had previously quantified in Connell's Davies Creek forest dynamics plot in Queensland, Australia.)  My own observations in Panama suggest that a key culprit causing non-random (possibly both density- and distance-dependent) early-stage mortality in Tetragastris panamensis (Burseraceae) – one of the most common canopy trees on the BCI FDP – is a somewhat host-specific pit-galling homopteran that appears to "rain" down from conspecific adult canopies; this is one of the key mechanisms Janzen imagined when he proposed his version of the Janzen-Connell hypothesis.

 

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Sodium in Phytocationic Landscapes and
as a Keystone Element for Community Ecology

Adriana Bravo's experiments and observations at the Los Amigos Biological Station in lowland Peru supported our hypothesis that frugivorous stenodermatine bats (a subfamily of leaf-nosed bats) visit collpas (clay licks) to obtain sodium that is otherwise in short supply in their diets (Bravo et al. 2008, 2010a, 2010b, 2012).  

Adriana's bat project expanded into an investigation of the biogeography of sodium availability in keystone resources (fig [Ficus] fruits) throughout the Neotropics.  For the project, Adriana obtained dried fruit specimens from herbaria, curated from collections across Central and South America (Bravo & Harms 2017).  Our observations concerning orders-of-magnitude differences among sites in sodium availability to frugivores, as well as the widespread geographic patterning of extremely low-sodium fruits, cause me to think of sodium as a "keystone element" in community ecology:  it is disproportionately important to consumers – far beyond its often meager availability to them. 

Luis Santiago-Rosario's systematic literature review and analysis of 107 plant populations (67 species in 20 plant families) grown under controlled laboratory and greenhouse conditions, demonstrated that even though plants vary in their growth responses to substrate-sodium concentrations, plant tissues generally become monotonically saltier as substrate saltiness increases (Santiago-Rosario et al. 2021).  This observation gave rise to our no-escape-from-sodium statistical hypothesis, by which we predicted that on average plants in saltier soils in nature have saltier tissues.  To test the prediction and to better understand the consequences for organisms at higher trophic levels, Luis's project expanded into an investigation of phytocationic landscapes (e.g., Santiago-Rosario et al. 2022; this is Mark Hunter's phytochemical landscape concept applied to cations).

In addition to his aforementioned work on the sodium-relationships between plants and their substrates, Luis also studied several aspects of the sodium-relationships between plants and their herbivores.  For example, he designed hydroponic methods to relatively precisely produce sunflower host plants of varying levels of saltiness and then asked how the bordered patch butterfly (Chlosyne lacinia [Nymphalidae]) responded (for an overview of the natural history of this extraordinary species, see Phelps et al. 2023).  One dramatic consequence of low-sodium diets was sibling cannibalism among these otherwise herbivorous caterpillars (Santiago-Rosario et al. 2023).

 

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Soil-Borne Plant Resources Shape Diversity, Dynamics & Structure of Forests Worldwide

Plant distribution patterns are often biased with respect to environmental variables (e.g., soil chemistry, moisture) or landscape features (e.g., topography).  The nature of the biases, especially the extent to which they differ among species and their underlying causes, helps sort among alternative mechanisms for the maintenance of species diversity and other emergent properties of community assembly. 

Collaborators and I have found distributional biases in several of the Center for Tropical Forect Science (CTFS – a research branch of the Smithsonian Tropical Research Institute [STRI]; now ForestGEO) Forest Dynamics Plots (FDPs).  To assess patterns of association between mapped stems and delineated habitats, I developed the novel Torus-Translation Test – a point-pattern statistical method that employs a toroidal randomization or null model.  We introduced the Torus-Translation Test using data from the Barro Colorado Island (BCI), Republic of Panama FDP (Harms et al. 2001).  Collaborators and I also found distributional biases with respect to topography in the Korup, Cameroon FDP (Chuyong et al. 2011) and the Sinharaja, Sri Lanka FDP (Gunatilleke et al. 2006).  In similar studies, we found biased distributions with respect to soil types among lianas in Sabah, Malaysia (DeWalt et al. 2006) and with respect to soil and topographic variables among trees in the Brazilian Amazon (Laurance et al. 2010). 

To better understand the underlying processes that generate spatial patterns of tropical tree and liana distribution, diversity, and dynamics, Jim Dalling (University of Illinois), Robert John-Chandran (Indian Institute of Science Education & Research), Joe Yavitt (Cornell University), Bob Stallard (U. S. Geological Survey), and I systematically characterized soil properties and hydrology of selected CTFS FDPs.  Our soil project stimulated similar assessments by other research groups in many of the temperate and tropical CTFS FDPs.  Soil-chemical and hydrologic spatial patterns help explain many individual species' distributional patterns and assemblage-level compositional patterns in forests throughout the world (e.g., Baldeck et al. 2013a, b, c, 2016 [trees at BCI and 7 other African, Asian & Neotropical FDPs]; Dalling et al. 2012 [lianas at BCI]; John et al. 2007 [trees at BCI and 2 other Neotropical FDPs]). 

We thank the National Science Foundation (grants DEB #0211004, OISE #0314581) and the Smithsonian Tropical Research Institute for supporting our initial soil and hydrology collaborative effort, including our soil-sampling, soil-analysis, and data-analysis training workshops in Panama, which expanded sampling and assessments to additional sites within the CTFS network and beyond.

 

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Nutrient Cycling & Limitation in a Lowland Old-Growth
Tropical Forest on the Isthmus of Panama

To test a variety of predictions concerning nutrient cycling and limitation of lowland tropical forests, since 1998 we have been adding nutrients to 40x40-m plots of relatively old-growth forest on the Gigante Peninsula of the Barro Colorado Nature Monument of the Smithsonian Tropical Research Institute (STRI), Republic of Panama (Santiago et al. 2012; Sayer et al. 2012; Woods et al. 2018; Wright et al. 2011; Yavitt et al. 2009, 2011).  We have four replicates of an NPK-factorial design, plus separate micronutrient plots.

Key results from the experiment support the growing awareness of multi-nutrient limitation of ecosystem processes (e.g., decomposition, Kaspari et al. 2008; productivity) and the limited responsiveness of old-growth forests to anthropogenic nutrient additions (at least over several years to a few decades, i.e., short time scales relative to tree lifetimes; Wright et al. 2018).

Joe Wright (STRI), Joe Yavitt (Cornell University), and I conceived the idea and designed the project; then together with Milton García we initiated fieldwork in 1997 (to determine baseline conditions prior to nutrient amendments).  As Joe Wright has maintained the project from his base at STRI, several ecologists, ecophysiologists, and biogeochemists have used our experiment as a springboard from which to further advance our understanding of nutrient cycling and limitation in tropical forests, including:  Mike Kaspari (University of Oklahoma), Jennifer Powers (University of Minnesota), and Lou Santiago (University of California at Riverside), among others. 

We thank the Smithsonian Institution and the Smithsonian Tropical Research Institute for supporting this project.

 

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Diversity & Dynamics in Intact & Fragmented Tropical Forests
of Central Amazonian Brazil

As the project's original Principal Investigators (PIs), Alexandre "Ale" Adalardo de Oliveira (Universidade de São Paulo, Brazil) and I spear-headed an effort to better understand forest diversity and dynamics in intact forests of the central Amazon Basin by adding a new node to the network of Forest Dynamics Plots (FDPs) coordinated by the Center for Tropical Forest Science (CTFS – a research branch of the Smithsonian Tropical Research Institute [STRI]; now ForestGEO).  With abundant help from Liz Losos (who was then the Director of CTFS), Rita Mesquita (who was then the Scientific Director of the Biological Dynamics of Forest Fragments Project), and many others, we created a square, 49-ha (700x700-m) FDP within the continuous, old-growth forest north of Manaus, Brazil.  Within the central, innermost 25-ha (500x500-m) square, all free-standing woody stems ≥1-cm diameter have since been mapped, measured, identified to species , and uniquely tagged for future re-measurements.  Our FDP contains >1200 species – more than any other large-scale plot in the network.

Ale and Alberto "Beto" Vicentini (Instituto Nacional de Pesquisas da Amazônia) now manage the project as its current PIs.  Stand data from our Manaus FDP are being used in a variety of global comparisons among forests (e.g., Réjou-Méchain et al. 2014).  Visit the Smithsonian Institution's Forest Global Earth Observatories (ForestGEO) web page of our Manaus FDP for a few additional details about the project.  Also, keep abreast of ForestGEO developments through the ForestGEO blog and via the ForestGEO photostream at Flickr.  We thank the Brazilian Government, CTFS, ForestGEO, the Louisiana Board of Regents, and the Richard & Rhoda Goldman Fund for supporting our project.

In a separate, but coordinated endeavor, I collaborated with Bill & Sue Laurance (James Cook University, Cairns, Australia) and the Biological Dynamics of Forest Fragments Project (BDFFP) in Brazil to better understand changes that occur in Amazonian forests when they are anthropogenically fragmented (e.g., Laurance et al. 2006).  With funding from the National Science Foundation (grant DEB #0614044), we conducted the first comprehensive census of sapling recruits (1 to 10-cm diameter) in subplots within the 1-ha phytodemographics plots that are strategically located in fragments and associated continuous forests across the BDFFP landscape.

 

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Adaptive & Aesthetic Evolution of Plant Traits,
Especially Owing to Their Interactions with Other Species
(Herbivores, Pollinators, Seed Dispersers, etc.)

Unusual organismal traits beg for ultimate explanations, i.e., why (in an evolutionary sense) do they exist?  Such explanations require understanding the ecological consequences of the traits for the organisms that possess them.  In the first section on this webpage, I gave the example of plants with highly flammable tissues that thrive in fire-frequented ecosystems.  In subsequent sections, I give two further examples:  "trash basket" architecture for nutrient acquisition in a tropical montane treelet and water calyces for floral defense in a tropical lowland herbaceous plant.

My earliest contributions – with Jim Dalling (University of Illinois) – toward better understanding adaptive traits in plants concerned the importance of resprouting to the recruitment ecology and life-history evolution of large-seeded trees and lianas (e.g., Dalling et al. 1997; Dalling & Harms 1999; Harms et al. 1997; Harms & Dalling 1997). 

In the course of working with big seeds, I discovered a new species of clearwing moth (Carmenta foraseminis [Sesiidae]), whose larvae tunnel through the large seeds of Gustavia superba (Lecythidaceae; Harms & Aiello 1995). 

Many adaptive or aesthetic plant traits influence the animals with which they interact.  Seed dispersal, herbivory, pollination, etc. are all shaped by evolution, sometimes co-evolution (reciprocal evolution of each partner in response to the other), as well as learning and cultural transmission among the animal interactors.  In this context, I am interested in the extent to which contrasting pollen on petals in some plants might influence the behavior of potential pollinators (Harms 2020).

Australia's showy mistletoes (Loranthaceae) express a variety of interesting traits.  For example, some of these parasitic species develop flashy floral displays, yet are otherwise rather cryptic, i.e., they resemble their hosts (e.g., their leaves are shaped like their hosts' leaves; Harms et al. 2023).  In addition, some have higher-quality, faster-turnover leaves than their hosts and appear to ramp-up local nutrient cycling in the immediate vicinity of the host.  Together with Sarah Mathews (LSU), Luis Santiago-Rosario (University of Minnesota), Arthur Porto (University of Florida), and Dave Watson (Charles Sturt University, Australia), we are contributing toward better understanding these plants' traits and their interactions with other organisms.

Collaborators and I have also explored several relationships among the functional, morphological, and physiological traits of plants, as well as their demographic characteristics (e.g., Poorter et al. 2008; I. J. Wright et al. 2007; S. J. Wright et al. 2010).

 

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"Trash Basket" Trade-off:  Light- vs. Nutrient-Capture
in Quadrella antonensis (Capparaceae)

Quadrella antonensis (formerly Capparis antonensis [Capparaceae]) is an unusual montane cloudforest treelet, endemic to the Republic of Panama.  At our study site in Altos de Campana National Park, individuals sacrifice light-capture efficiency to obtain nutrients through aboveground adventitious roots that access decomposing leaf litter held in the "trash baskets" formed from the plant's own closely-spaced leaves (Harms, Dalling & Sánchez de Stapf 2020 – a Flora Obscura contribution to The New Phytologist Trust's Plants, People, Planet; enjoy the brief YouTube video summary).  In our article we compare and contrast litter trapping with botanical carnivory and certain types of myrmecophily as alternative nutrient-acquisition strategies.  Jim Dalling (University of Illinois) and I worked on the basic litter-trapping biology; María Sánchez de Stapf (Universidad de Panamá) collaborated with us and completed a master's thesis by conducting a litter-removal experiment (which empirically demonstrated the performance advantage to these plants of trapping litter); and Bob Pearcy (University of California at Davis) contributed toward understanding the plant's nutrient uptake and self-shading.  We thank the Smithsonian Tropical Research Institute for supporting this project.

 

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Water Calyces Dissuade Specialist Floral Enemies
in Chrysothemis friedrichsthaliana (Gesneriaceae)

Chrysothemis friedrichsthaliana (Gesneriaceae) develops water calyces, i.e., upright calyces that fill with water which covers the additional floral structures during their early development.  Jane Carlson's experiments on the Osa Peninsula of Costa Rica demonstrated that flowers with experimentally drained calyces suffered higher rates of attack by a microlepidopteran floral herbivore (Alucita sp. cf. flavicincta [Alucitidae]), supporting the adaptive hypothesis that water calyces dissuade specialist floral enemies (Carlson & Harms 2007).

 

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Behavioral Ecology & Evolution

Even though most of my current research has a plant-ecology focus, I have an abiding interest in behavioral ecology.  Natural history has aroused my curiosity and sense of wonder for as long as I can remember, but as an undergraduate I was especially intrigued by animal behavior.  For example, I was a field assistant to Bill Franklin and Warren Johnson (who were then professor and Ph.D. student, respectively, at Iowa State University) for 7 months in Torres del Paine National Park, Chile – where I helped study the foraging and social behavior, as well as inter-specific interactions, of some of the park's carnivores (puma [Puma concolor; see Bill Franklin's National Geographic article – I am the "student assistant" on pg. 109]; two species of fox [Lycalopex culpaeus; L. griseus]; Geoffroy's cat [Leopardus geoffroyi]; and Patagonian hog-nosed skunk [Conepatus humboldtii]).  I also completed an undergraduate honors thesis from my investigation of sex-biased juvenile dispersal in guanacos (Lama guanicoe). 

Just prior to graduate school, I was a field assistant to Gordon Orians and Les Beletsky (who were then professor and post-doc, respectively, at the University of Washington) on a long-term study of the courtship, mating, nesting, and parental behavior of three species of icterid blackbirds (red-winged blackbird [Agelaius phoeniceus]; Brewer's blackbird [Euphagus cyanocephalus]; and yellow-headed blackbird [Xanthocephalus xanthocephalus]) in eastern Washington (Harms et al. 1991).

In graduate school and beyond, I have enjoyed tagging along on some of Jessica Eberhard's research trips.  During one of those trips, we documented the communal roosting behavior of parrots, doves, and pigeons on Aruba, Bonaire, Curaçao, and Isla Margarita, Venezuela (Harms & Eberhard 2003). 

Sandra Galeano's experiments and observations in the Bocas del Toro Archipelago, Republic of Panama supported our prediction that males from aposematic, brightly-colored populations of the highly polymorphic / polytypic frog, Oophaga pumilio, would be more aggressive toward both conspecific and heterospecific males than would be individuals from cryptic populations (Galeano & Harms 2016).  Sandra's project helps link the evolution of behavioral and morphological traits in O. pumilio via natural and sexual selection to their community-level contexts and consequences.

I am grateful to my many collaborators (students, post-docs, professors, and other friends) who have helped me nurture a wide range of interests during my thoroughly enjoyable research career!