Biology subjects

Cristescu, M.

Publications and source records attributed to Cristescu, M..

3 recordsLinked to original sources

bioRxiv2023

Ecosystem connectivity and configuration can mediate instability at a distance in metaecosystems

Ecosystems are connected by flows of nutrients and organisms. Changes to connectivity and nutrient enrichment may destabilise ecosystem dynamics far from the nutrient source. We used gradostats to examine the effects of trophic connectivity (movement of consumers and producers) versus nutrient-only connectivity in different metaecosystem configurations (linear vs dendritic) on dynamics of Daphnia pulex (consumers) and an algae (resources). We found that peak population size and instability (coefficient of variation; CV) of Daphnia populations increased as distance from the nutrient input increased, but were lower in metaecosystems connected by all trophic levels compared to nutrient-only connected systems and in dendritic systems compared to linear ones. We examined the effects of trophic connectivity (i.e. how many trophic levels are moving rather than one or the other) using a generic model to qualitatively assess patterns of ecosystem dynamics. Our model predicted increased population sizes and fluctuations in ecosystems with nutrient connectivity, with this pattern being more pronounced in linear rather than dendritic systems. These results confirm that connectivity may propagate and even amplify instability over a metaecosystem to communities far from the source disturbance, and suggest a pathway for future experiments, that recreate conditions closer to those found in natural systems.

ecology↗

bioRxiv2020

Ecosystem Entanglement and the Propagation of Nutrient-Driven Instability

Almost 50 years ago, Michael Rosenzweig pointed out that nutrient addition can destabilize food webs, leading to loss of species and reduced ecosystem function through the paradox of enrichment. Around the same time, David Tilman demonstrated that increased nutrient loading would also be expected to cause competitive exclusion leading to deleterious changes in food web diversity. While both concepts have greatly illuminated general diversity-stability theory, we currently lack a coherent framework to predict how nutrients influence food web stability across a landscape. This is a vitally important gap in our understanding, given mounting evidence of serious ecological disruption arising from anthropogenic displacement of resources and organisms. Here, we combine contemporary theory on food webs and meta-ecosystems to show that nutrient additions are indeed expected to drive loss in stability and function in human-impacted regions. However, this loss in stability occurs not just from wild oscillations in population abundance, but more frequently from the complete loss of an equilibrium due to edible plant species being competitively excluded. In highly modified landscapes, spatial nutrient transport theory suggests that such instabilities can be amplified over vast distances from the sites of nutrient addition. Consistent with this theoretical synthesis, the empirical frequency of these distant propagating ecosystem imbalances appears to be growing. This synthesis of theory and empirical data suggests that human modification of the Earths ecological connectivity is "entangling" once distantly separated ecosystems, causing rapid, expansive, and costly nutrient-driven instabilities over vast areas of the planet. The corollary to this spatial nutrient theory, though -- akin to weak interaction theory from food web networks -- is that slow spatial nutrient pathways can be potent stabilizers by moderating flows across a landscape.

ecology↗

bioRxiv2018

Highly accelerated rates of heritable large-scale mutations under prolonged exposure to a metal mixture of copper and nickel

Mutation rate variation has been under intense investigation for decades. Despite these efforts, little is known about the extent to which environmental stressors accelerate mutation rates and influence the genetic load of populations. Moreover, most studies have focused on point mutations rather than large-scale deletions and duplications (copy number variations or \"CNVs\"). We estimated mutation rates in Daphnia pulex exposed to low levels of environmental stressors as well as the effect of selection on de novo mutations. We conducted a mutation accumulation (MA) experiment in which selection was minimized, coupled with an experiment in which a population was propagated under competitive conditions in a benign environment. After an average of 103 generations of MA propagation, we sequenced 60 genomes and found significantly accelerated rates of deletions and duplications in MA lines exposed to ecologically relevant concentrations of metals. Whereas control lines had gene deletion and duplication rates comparable to other multicellular eukaryotes (1.8 x 10-6 per gene per generation), a mixture of nickel and copper increased rates fourfold. The realized mutation rate under selection was reduced to 0.4x that of control MA lines, providing evidence that CNVs contribute to mutational load. Our CNV breakpoint analysis revealed that nonhomologous recombination associated with regions of DNA fragility is the primary source of CNVs, plausibly linking metal-induced DNA strand breaks with higher CNV rates. Our findings suggest that environmental stress, in particular multiple stressors, can have profound effects on large-scale mutation rates and mutational load of populations.

genomics↗