Research

Ecological model testing, multispecies coexistence, community assembly, monitoring and eco-evolutionary research at the WEBS Group, UCLA.

Blind Monks Examining an Elephant by Hanabusa Itchō
英一蝶 Hanabusa Itchō, Blind Monks Examining an Elephant, 1888, Library of Congress

Testing ecological models

Which ecological models remain compatible with observations when much of the system is hidden? We develop tests that can reject candidate models without observing every species or driver.

Covariance criteria link observable population gains and losses through necessary conditions for a model. In a selected set of 172 population time series, the classic logistic model passed the covariance test in only 10 cases. Comparing 18 predator–prey series without major rapid evolution with 13 where it was observed revealed deviations from the baseline Lotka–Volterra form in predator dynamics. Under the test’s assumptions, a violated condition rules out the candidate model; passing does not prove it correct. Observation quality and the sampling needed to estimate the quantities remain important.

A complementary preprint on label invariance asks whether predictions change when identical individuals are split into arbitrary groups. Together with our work comparing theoretical frameworks, these projects ask both how to test a model and which scientific job it is built to do.

Key references

9

In the pipeline

4
  • Label invariance: a diagnostic for ecological models. Submitted; public preprint. Gibbs T et al.
  • When does heterogeneity average out in coarse-grained ecological communities?. Submitted. Luo M et al.
  • A trilemma of ecological complexity. In preparation. Metz T et al.
  • Lotka–Volterra at 100: a more honest starting point. In preparation. Song C
Five-Colored Parakeet by Emperor Huizong
宋徽宗 Emperor Huizong of Song, 《五色鸚鵡圖》 (Five-Colored Parakeet), detail, c. 1115, Museum of Fine Arts, Boston

Coexistence of many species

How do many species coexist, and how does environmental change alter their opportunities to persist? We connect multispecies theory with interactions across trophic levels, environmental variation and empirical estimates of species interactions.

Our structural approaches measure the range of model conditions compatible with coexistence. This is a way to assess coexistence opportunities under specified dynamics; it is distinct from directly observing indefinite persistence in a field community. Published studies examine network structure and species abundance, phenology, individual variation, soil microbes and multitrophic interactions.

A submitted manuscript investigates whether finite within-species budgets can support coexistence without between-species trade-offs. A second examines constraints on annual-plant interactions across variable rainfall. Work on fluctuating environments asks how the timing of conditions changes the conclusions drawn from averages.

Key references

16

In the pipeline

4
  • Multispecies coexistence does not require trade-offs between species. Submitted. Max D et al.
  • The standard plant–soil feedback model underpredicts coexistence. Submitted. Max D et al.
  • Species interactions are internally constrained despite large climatic variability. Submitted; public preprint. Picó S et al.
  • Community response and the temporal niche in variable environments. In preparation. Barabás G et al.
Möbius Strip II by M.C. Escher, red ants walking a one-sided loop
M.C. Escher, Moebius-band met rode mieren (Möbius Strip II, Red Ants), 1963

Assembly and priority effects

Does the order in which species arrive determine the community that forms? We use topology, graph theory and information theory to distinguish history-dependent assembly outcomes from outcomes fixed by the system and its conditions.

The possible priority effects multiply super-exponentially with species number, yet our framework reduces them to four basic types. Coexistence holes, gaps among possible communities, make assembly and disassembly discontinuous. Assembly graphs connect assemblages through species introductions and the transitions that follow. These representations help make questions about arrival order explicit and identify which outcomes can be reached.

For experimental use, an introduction sequence and the community it produces define a candidate transition. Repeating sequences can reveal variation in outcomes; the representation must be interpreted alongside the observation timescale and community definition. Our published assembly-graph review connects theoretical approaches with measurable components. Ongoing microbial work examines how antibiotic-resistance evolution affects assembly predictability.

Key references

6

In the pipeline

1
  • Antibiotic resistance evolution and the predictability of bacterial community assembly. In preparation. Hogle SL et al.
D'Arcy Thompson's coordinate transformation of a porcupine fish into a sunfish
D’Arcy Wentworth Thompson, On Growth and Form, figs. 381–382 (porcupine fish transformed into sunfish), 1917, Cambridge University Press

Geometry and physics of communities

What do geometry and physics reveal about community responses to change? We use these tools to pose ecological questions about sustained pressures, temporal dynamics and differences among assemblages.

A submitted manuscript on structural sensitivity studies which directions of sustained environmental change a community amplifies or absorbs. A public preprint on time irreversibility measures how population time series differ when played forward and backward, with applications involving evolution, nutrient supply and temperature.

Our published geometric approach to beta diversity measures assemblage structure from a different perspective than conventional pairwise dissimilarity. The useful choice depends on the ecological question: a complementary measure is not a universal replacement. Related published work connects dynamical and structural indicators of resilience and examines swarming systems.

Key references

4

In the pipeline

2
Alexander von Humboldt and Aimé Bonpland's Naturgemälde der Anden, plants mapped by elevation on Chimborazo
Alexander von Humboldt and Aimé Bonpland, Naturgemälde der Anden (Natural Painting of the Andes), detail, 1807, Zentralbibliothek Zürich

Monitoring and global change

What can partial surveys reliably tell us about persistence, and how are communities responding to invasions, land use and fire? We connect limited observations to specific ecological inferences, rather than treating every kind of missing data as the same problem.

Our published monitoring work uses small interaction subnetworks as probabilistic indicators of larger-network persistence. In the Seychelles pollination-network application, we estimated that monitoring five plant species could reduce combined plant-observation and insect-identification costs by 42%. That estimate depends on the study system and monitoring target. Related work studies what incomplete patch surveys can reveal about metapopulation persistence. Imperfect detection, missing species and missing interactions require attention to the assumptions of each method.

Applied studies examine habitat fragmentation and mutualistic assemblages, and land consolidation, rodent communities and disease transmission. Current manuscripts investigate introduced species in seed-dispersal communities, functional-richness measures and the relationship between fuel-treatment hazard reduction and ecological restoration.

Key references

4

In the pipeline

3
  • Introduced species erode the stability of seed-dispersal communities worldwide. Submitted. Song C et al.
  • A mismatch in hazard reduction and ecological restoration in western US fuel treatments. Submitted. Metz T et al.
  • Using alpha shapes to measure functional richness: a novel methodology. Submitted. Guoli Z et al.
Two red-breasted geese from the Geese of Meidum, tomb of Itet, Egypt
Unknown artist, The Geese of Meidum, tomb of Itet, detail, c. 2600 BCE, Egyptian Museum, Cairo

Ecology meets evolution

How do ecological and evolutionary change shape each other? This newer direction has two connected strands: feedbacks between organisms and communities, and the evolution of trait distributions.

Ecological and evolutionary feedbacks. Published model-testing work examines predator–prey systems with rapid evolution. Submitted manuscripts develop a theory of host–microbiome speciation and investigate predators and antibiotic-resistant microbial strains.

Trait distributions and adaptation. Work in preparation asks how reproductive transmission and selection shape trait distributions, when approximately Gaussian distributions arise, how skewness affects changes in trait variance, and how geometry constrains adaptation in changing environments.

Key references

1

In the pipeline

6
  • A theory of holobiont speciation. Submitted. Yang H et al.
  • Microfaunal predators maintain antibiotic resistant strains in microbial communities. Submitted. Hogle SL et al.
  • Geometric constraints on adaptation in changing environments. In preparation. Song C
  • Skewness shields trait variance from natural selection. In preparation. Song C et al.
  • Whence Gaussian: a reproductive renormalization group in quantitative genetics. In preparation. Song C
  • Conditional chaos limits for prospective Mendelian transmission under selection. In preparation. Song C