A mechanistic analysis of density dependence in algal population dynamics

Conspecific density may influence adult recruitment and consequently population dynamics. Several studies have shown the density dependence of larvae growth rates in Odonata. However, few studies studied how conspecific density influence final instar larvae emergence date decisions. Considering that larvae may choose the date of emergence, the present study investigated if density affects larvae choice. For this, we reared eight final instar larvae in individual aquaria and other 24 larvae in aquaria with three larvae each. This way, we simulated environments with low and high larval densities. We then noted the days that larvae took to emerge and compared it between low and high density groups. The results showed that larvae seem to emerge earlier when in high densities (Mann-Whitney,U=10.000,P=0.03). These results support the hypothesis that damselfly last instar larvae may postpone or hasten emergence in response to the social environment and related constraints.

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Population dynamics of muskrats and mink: investigating contemporary patterns in a classic predator-prey system

Canadian Journal of Zoology ◽

10.1139/cjz-2020-0296 ◽

2021 ◽

Author(s):

Adam A Ahlers ◽

Timothy P Lyons ◽

Edward J Heske

Keyword(s):

United States ◽

Population Dynamics ◽

Density Dependence ◽

American Mink ◽

Population Cycles ◽

The United States ◽

Parameter Estimates ◽

Predator Prey ◽

Cycle Lengths ◽

Southern Half

A well-studied predator-prey relationship between American mink (Neovison vison (Schreber, 1777)) and muskrats (Ondatra zibethicus (Linnaeus, 1766)) in Canada has advanced our understanding of population cycles including the influence of density dependence and lagged responses of predators to prey abundances. However, it is unclear if patterns observed in Canada extend across the southern half of their native range. We used data from the United States to create a 41-year time series of mink and muskrat harvest reports (1970-2011) for 36 states. After controlling for pelt-price effects, we used 2nd order autoregressive and Lomb-Scargle spectral density models to identify the presence and periodicity of muskrat population cycles. Additionally, we tested for evidence of delayed or direct density dependence and for predator-driven population dynamics. Our results suggest muskrat populations may cycle in parts of the United States; however, results varied by modeling approaches with Lomb-Scargle analyses providing more precise parameter estimates. Observed cycle lengths were longer than expected with weak amplitudes and we urge caution when interpreting these results. We did not detect evidence of a predator-prey relationship driven by a lagged numerical response of American mink. American mink and muskrat fur returns were largely correlated across the region suggesting extraneous factors likely synchronize both populations.

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