Harvested populations are more variable only in more variable environments

Abstract

The interaction between environmental variation and population dynamics is of major importance, particularly for managed and economically important species, and especially given contemporary changes in climate variability. Recent analyses of exploited animal populations contested whether exploitation or environmental variation has the greatest influence on the stability of population dynamics, with consequences for variation in yield and extinction risk. Theoretical studies however have shown that harvesting can increase or decrease population variability depending on environmental variation, and requested controlled empirical studies to test predictions. Here, we use an invertebrate model species in experimental microcosms to explore the interaction between selective harvesting and environmental variation in food availability in affecting the variability of stage‐structured animal populations over 20 generations. In a constant food environment, harvesting adults had negligible impact on population variability or population size, but in the variable food environments, harvesting adults increased population variability and reduced its size. The impact of harvesting on population variability differed between proportional and threshold harvesting, between randomly and periodically varying environments, and at different points of the time series. Our study suggests that predicting the responses to selective harvesting is sensitive to the demographic structures and processes that emerge in environments with different patterns of environmental variation.

Trait‐based predictions and responses from laboratory mite populations to harvesting in stochastic environments

“…In our experiment, similar to findings by Cameron et al. () for S. berlesei , the effect of harvesting on life stage counts depended on the colour of the environmental noise. In all environments, large‐adult harvesting reduced the mean adult counts; however, in red environments, in contrast to the blue or white environments, this reduction in adult counts did not carry over to reduce egg and juvenile counts.…”

“…One general pattern that has emerged is how noise colour interacts with density dependence (Kaitala et al., ): a population with undercompensating growth reacts slowly to environmental changes, whereas overcompensating populations overshoot their equilibrium after a perturbation. Bulb mite population growth has been characterised as overcompensating (Cameron & Benton, ; Cameron et al., ). We found that the type of compensating response in the mite populations to the single harvesting rate that we investigated was an interaction between noise colour and harvesting rate, as compensation to harvesting in terms of population growth was not achieved, thus showing undercompensation.…”

A functional trait approach to identifying life history patterns in stochastic environments

“…Unraveling the drivers of population growth in variable environments is critical for answering eco‐evolutionary questions (Ruokolainen, Linden, Kaitala, & Fowler, ; Smallegange, Deere, & Coulson, ; Tuljapurkar, ), developing conservation management strategies (Clark, ; Metcalf & Koons, ), predicting the time course of epidemics (Chaves, Scott, Morrison, & Takada, ; Keeling & Gilligan, ) and in influencing the yield of harvested populations (Cameron et al, ; Higgins, Hastings, Sarvela, & Botsford, ; Smallegange & Ens, ). Both demographic processes and temporal variation in environmental conditions are important drivers of population growth (Higgins et al, ; Lande, Engen, & Sæther, ; Turchin & Taylor, ).…”

Does harvesting amplify environmentally induced population fluctuations over time in marine and terrestrial species?

“…This finding has been further discussed by Sugihara et al (). Recently, Cameron et al () experimentally tested the hypothesis of enhanced fluctuations in population size when adult/old individuals were removed using a terrestrial species, the soil mite ( Sancassania berlese ). The experiment consisted of different harvesting treatments under different regimes of environmental fluctuations.…”

“…Seasonal migration is a widespread phenomenon in vertebrates, Only when environmental variation and harvesting were combined did we see strong evidence of magnified fluctuations in abundance." Cameron et al, 2016 being observed in fish, birds and mammals (Milner-Gulland, Fryxell, & Sinclair, 2011). Migration patterns can be culturally transmitted through social learning in both marine (Corten, 2002) and terrestrial environments (Jesmer et al, 2018).…”