Biology subjects

Lennox, R. S.

Publications and source records attributed to Lennox, R. S..

3 recordsLinked to original sources

bioRxiv2026

Population and community responses to the fast, slow, and seasonal components of environmental variation

Theory suggests that different components of environmental fluctuations, from daily and seasonal cycles to multidecadal trends, can have distinct and even opposing effects on species abundances and community dynamics, depending on their specific adaptations. But empirical research that deconstructs the influence of these different cycles on communities is lacking. Here, we used long-term biological monitoring data together with flow records of rivers across New Zealand to (i) investigate the role of fast, slow, and seasonal river-flow fluctuations in structuring macroinvertebrate communities; and (ii) to assess whether life-history and mobility traits mediate the response. Using joint species distribution models, we found striking differences in taxon and community responses to the different components of river flow variation. Responses to slow fluctuations were generally stronger and better predicted by traits, while responses to seasonal fluctuations were highly heterogeneous. Fast increases in flow, typical of flooding events, had pervasive negative effects on species abundances, but the severity of impact partly depended on mobility traits. Our results suggest that different ecological mechanisms underpin the response to distinct environmental fluctuations, highlighting the value of jointly considering multiple temporal scales of variation and species functional traits to understand and predict how communities reorganise under fluctuating environmental regimes.

ecology↗

bioRxiv2025

Disturbance provides limited respite for native fish against invaders

Understanding how flow-related disturbance regimes influence species interactions is critical for conserving threatened species in freshwater ecosystems, where both the alteration of these regimes and the invasion of non-native species pose major threats. Using 30 years of sampling data from a well-studied river system in Aotearoa New Zealand, we applied empirically- parameterized Lotka-Volterra competition models across a gradient of flood disturbance regimes to assess the potential for coexistence between threatened native galaxiids and invasive trout. Our models suggest trout dominate under low disturbance regimes, leading to galaxiid extinction. Coexistence peaks at intermediate disturbance regimes, though native fish densities are highly suppressed. Only at high disturbance regimes do native fish prevail, but priority effects are likely. Thus, restoration and conservation efforts focused solely on high disturbance habitats without accompanying biological interventions may not ensure native fish persistence. Further, prioritizing such habitats at the expense of others risks misdirecting resources towards sub-optimal conditions, particularly under climate change.

ecology↗

bioRxiv2024

Introduced trout hinder the recovery of native fish following an extreme flood disturbance

O_LIIn rivers, we are seeing a shift away from natural flow regimes towards larger and more frequent extreme drought and flood events. However, it is unclear how increasing intensity and frequency of extreme flow disturbances will play out alongside existing biotic pressures, such as biological invasions, to impact aquatic biodiversity. In New Zealand, vulnerable native non-diadromous galaxiid fishes face pressure from introduced trout through interspecific competition and predation, which may influence the recovery of native galaxiids after flood disturbances. C_LIO_LIHere, we employed a capture-mark-recapture study across 12 sites, along a gradient of disturbance following a major flood event, to examine the impact of extreme flooding on the population structure of non-diadromous galaxiids (Galaxias vulgaris and G. paucispondylus), and the effect of trout presence on individual galaxiid growth rates recovering from this event. C_LIO_LIWe found a lower abundance of all non-diadromous galaxiid size classes under higher flood magnitudes, but smaller size classes (i.e., young-of-year and 1-2 year cohorts) were more impacted. C_LIO_LIFurthermore, the presence of trout, whether at low or high abundances, reduced the individual growth of native non-diadromous galaxiids, despite interspecific effects being a weaker regulator of individual growth compared to conspecific effects. Moreover, trout effects on galaxiids varied by both galaxiid size and density, such that growth of smaller individual galaxiids in low densities were most affected by the presence of trout regardless of trout density. C_LIO_LIIn summary, our results demonstrate that non-diadromous galaxiid population dynamics in future are likely to be affected by flood disturbance regimes and introduced trout presence, the outcome of which involves a complex balance between reduced population persistence and increased individual resistance of larger individuals. C_LIO_LIConservation efforts that focus on maintaining strategically placed trout-free source populations of adult galaxiids could therefore be an important tool to enable native dispersal into trout-affected habitat and maintain population resilience in the face of increasingly larger and more frequent extreme events, given that recruitment of non-diadromous galaxiids is higher in the absence of trout. C_LI

ecology↗