Theoretical Ecology

Mallmin, Emil

doi: 10.1007/s12080-022-00547-9pmid: N/A

Simon, Margaret W.; Barfield, Michael; Holt, Robert D.

doi: 10.1007/s12080-022-00543-zpmid: N/A

All individuals transition through various life stages over the course of their development and nearly all organisms must contend with infectious disease at some point in their lives. Yet the intersection of these two universal features of life—stage structure and infectious disease—and their joint effects on population dynamics are poorly understood. Here, we develop a two-stage population model in which density dependence acts on juvenile maturation, and infectious disease affects either juveniles or adults via reduction in maturation, reproduction, or survival. In the absence of disease, this form of density dependence can generate persistent population oscillations. We examine whether infectious disease further accentuates these oscillations (by augmenting their amplitude) or stabilizes them (by reducing their amplitude). We find that, for moderate transmission rates (a proxy for disease incidence), disease can stabilize dynamics. In contrast, fast disease transmission is not generally stabilizing, which is, at least in part, due to disease overexploitation of the infectious class. Hydra effects are possible in the model due to density overcompensation and occur when disease increases juvenile mortality or decreases adult fecundity (but do not occur when disease augments adult mortality or reduces maturation). Slow maturation, large disease-free population size, and strong density-dependent population regulation can each lower the transmission rate required for the infectious disease to invade the population.Graphical abstract[graphic not available: see fulltext]

Vikrant, Ankit; Nilsson Jacobi, Martin

doi: 10.1007/s12080-022-00545-xpmid: N/A

It has been a century since the species-area relationship (SAR) was first proposed as a power law to explain how species richness scales with area. There have been many attempts to explain the origin of this predominant form. Apart from the power law, numerous empirical studies also report a semi-log form of the SAR, but very few have addressed its incidence. In this work, we test whether these relationships could emerge from the assembly of large random communities on island-like systems. The clustering of same-species individuals is central to our results, which we incorporate by modifying the self-interaction term in the generalized Lotka-Volterra equations. Our analysis demonstrates that the two most widely reported relationship forms can emerge due to differences in immigration rates and skewness towards weak interactions. We particularly highlight the incidence of the semi-log SAR for low immigration rates from a source pool, which is consistent with several previous empirical studies. The two SAR forms might show good fits to data over a large span of areas but a power-law overestimates species richness on smaller islands in remote archipelagoes.

Greiner, Ariel; S. Darling, Emily; Fortin, Marie-Josée; Krkošek, Martin

doi: 10.1007/s12080-022-00546-wpmid: N/A

Theory and empirical work suggest that coral reefs may exhibit alternative stable states of coral versus macroalgal dominance. However, it is unclear how dispersal of coral and macroalgae among reefs might impact this bistability and the resilience of the coral-dominated state. We develop a mathematical model to investigate how reef cover dynamics are affected by (1) coral and macroalgal dispersal between two reefs and (2) heterogeneous grazer abundances. We find that at low coral and macroalgal dispersal levels, a new type of stable state emerges with both coral and macroalgae present. Furthermore, we show that a reef abundant with coral and grazers can support a coral-dominated stable state in a second reef depauperate of grazers by dispersal of coral larvae. These results help explain previous empirical findings on reefs once thought to be incongruent with traditional coral-macroalgal alternative stable states theory—such as intermediate coral and macroalgal cover stable states and high coral-low grazing scenarios. Our findings indicate that changing dispersal levels (e.g., due to climate change, reef degradation) between reefs changes the possible stable states and the grazing rate at which the coral-dominated state is predicted to be stable. This work demonstrates the relevance of accounting for the level of dispersal among coral reefs or other bistable ecosystems when designing conservation management plans.