Memories of Trees Past: Coexistence Implications of Legacy Conspecific Density Dependence

Ecology Letters · 2025-10-01

The Janzen-Connell Hypothesis posits that plant species diversity is maintained by a reduction in seedling survival near living conspecific trees relative to heterospecifics-known as negative conspecific density dependence (CDD). CDD facilitates coexistence if stronger than heterospecific density dependence (HDD). However, whether and how long CDD persists after trees die is unknown. In a three-year study across three forests, we monitored seedling survival near living and dead trees, both conspecific and heterospecific, across a seven-year chrono-sequence since tree death. CDD persisted for at least 5 years after tree death ('legacy CDD'), and most species showed stronger CDD relative to HDD through time. We used our empirical findings to parametrize a theoretical community dynamics model. Our model suggests that both stabilising niche differences and fitness differences persist after tree death. While legacy CDD can facilitate coexistence, fitness differences often overwhelmed niche differences, making competitive exclusion the most likely outcome.

Memories of trees past: coexistence implications of legacy conspecific density dependence

2025-03-14

The Janzen-Connell Hypothesis posits that plant species diversity is maintained by a reduction in seedling survival near living conspecific trees relative to heterospecifics –known as negative conspecific density dependence (CDD). CDD facilitates coexistence if stronger than heterospecific density dependence (HDD). However, whether and how long CDD persists after trees die is unknown. In a three-year study across three forests, we monitored seedling survival near living and dead trees, both conspecific and heterospecific, across a seven-year chrono-sequence since tree death. CDD persisted for at least five years after tree death (‘legacy CDD’), and most species showed increasingly stronger CDD relative to HDD through time. We used our empirical findings to parametrize a theoretical community dynamics model. Our model suggests that both stabilizing niche differences and fitness differences persist after tree death. While legacy CDD can facilitate coexistence, fitness differences often overwhelmed niche differences, making competitive exclusion the most likely outcome.

Author response for "Memories of Trees Past: Coexistence Implications of Legacy Conspecific Density Dependence"

2025-07-11

Author response for "Memories of Trees Past: Coexistence Implications of Legacy Conspecific Density Dependence"

2025-06-13

Aging dynamics in captive sea turtles reflect conserved life-history patterns across the testudine phylogeny

Communications Biology · 2025-08-28 · 4 citations

Recent work has shown testudines can escape actuarial senescence for extended periods. However, understanding how the interplay between somatic aging and reproductive investment in highly fecund, long-lived ectotherms align with broader phylogenetic patterns remains a critical knowledge gap. Here, we present a comprehensive demographic analysis of age-specific changes in reproduction and mortality using a unique dataset on captive, known-aged green sea turtles Chelonia mydas. Despite substantial intraspecific variation, cumulative egg production showed no decline, increasing linearly for over two decades. However, mortality patterns followed the Gompertz Law, increasing exponentially with age. These results demonstrate a significant decoupling between sustained reproductive performance and age-specific mortality, building on a body of work that challenges the notion of uniformly arrested senescence. Nevertheless, life history strategies across testudines, including sea turtles, produce similar aging rates and remain low relative to endothermic tetrapods, reflecting conserved life-history patterns. Decades of captive green sea turtle data reveals no evidence of reproductive senescence despite mortality rates increasing with age. These results contextualize age-specific changes in the life history of sea turtles within the testudine phylogeny.

Telomeres and the Rate of Living: Linking Biological Clocks of Senescence

Ecological and Evolutionary Physiology · 2024-04-12 · 1 citations

AbstractTwo prominent theories of aging, one based on telomere dynamics and the other on mass-specific energy flux, propose biological time clocks of senescence. The relationship between these two theories, and the biological clocks proposed by each, remains unclear. Here, we examine the relationships between telomere shortening rate, mass-specific metabolic rate, and lifespan among vertebrates (mammals, birds, fishes). Results show that telomere shortening rate increases linearly with mass-specific metabolic rate and decreases nonlinearly with increasing body mass in the same way as mass-specific metabolic rate. Results also show that both telomere shortening rate and mass-specific metabolic rate are similarly related to lifespan and that both strongly predict differences in lifespan, although the slopes of the relationships are less than linear. On average, then, telomeres shorten a fixed amount per unit of mass-specific energy flux. So the mitotic clock of telomere shortening and the energetics-based clock described by metabolic rate can be viewed as alternative measures of the same biological clock. These two processes may be linked, we speculate, through the process of cell division.

Evaluating the tradeoff between offspring number and survivorship across fishes, amphibians, reptiles and mammals

Oikos · 2021-04-01 · 14 citations

Species differ widely in their strategies of resource allocation to offspring mass and number, ranging from teleost fishes and amphibians that produce many tiny offspring to reptiles and mammals that produce relatively few large offspring. Tradeoffs between offspring survivorship and fecundity are thought to limit the success of any particular reproductive strategy, but these tradeoffs have not been evaluated quantitatively across the full range of variability in offspring size and number. Here we examine the relationship of offspring size to reproductive success (i.e. fitness) within and across teleost fishes, amphibians, reptiles and mammals. To do so, we evaluate the relationships of offspring mass to survivorship (proportion of offspring surviving to maturity) and to fecundity (no. offspring/time). We show that survivorship tends to increase in proportion with relative offspring mass (offspring mass/adult mass), whereas fecundity, normalized to offspring biomass production rate, tends to decrease in proportion with offspring mass. Consequently, the product of survivorship and fecundity – reproductive success – is generally independent of offspring mass. Thus, our results show quantitatively how survivorship and fecundity tradeoff across diverse taxa to limit reproductive success.

Host cell volume explains differences in the size of DsDNA viruses

Virus Research · 2021-01-27 · 4 citations

Characterizing the microbiomes of Antarctic sponges: a functional metagenomic approach

Scientific Reports · 2020 · 67 citations

• Biology
• Ecology
• Botany

fixation mediated by chemoautotrophic microorganisms. Together, these results show how the unique metabolic potential of two Antarctic sponge microbiomes help these sponge holobionts survive in these inhospitable environments, and contribute to major nutrient cycles of these ecosystems.

Allometric scaling of Lyapunov exponents in chaotic populations

Population Ecology · 2020 · 14 citations

• Biology
• Ecology
• Statistical physics

Abstract Chaos has been a central topic of research in ecology for decades, in part because of its implications for the predictability of population dynamics. Chaotic systems are characterized by low predictability at long timescales, as slight differences in initial conditions (e.g., the actual vs. the measured initial conditions) yield trajectories (e.g., the actual vs. the predicted trajectory) that diverge exponentially at a rate determined by the global Lyapunov Exponent (LE). The LE is therefore a critical descriptor of chaotic systems that sets the time horizon for predictability. Recent observations of chaos in populations or communities have shown that LEs vary by at least two orders of magnitude, yet the factors underlying this variability remain unclear. Here, we examine the drivers of heterogeneity in LEs among chaotic populations and communities. We show that LEs decline with increasing body size as a shallow power law (exponent −0.21), suggesting that LEs are inversely proportional to the populations' generation time (GT). However, this allometric scaling relationship holds only when considering the larger, slower growing populations in multispecies communities (the primary and secondary consumers), indicating that these populations constrain or determine LEs for the community. These results suggest that the rate at which the predictability of a chaotic time series declines over time generally reflects either the populations' GT, or that of a slower growing population in the community.