Biological Annihilation

Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines (2017) Ceballos et al., Proceedings of the National Acadeemy of Sciences of the USA, DOI: https://doi.org/10.1073/pnas.1704949114

The sumatran orangutan, one of many species facing extinction in the earth's sixth mass extinction event
The sumatran orangutan, one of many species facing extinction in the earth’s sixth mass extinction event (Image Credit: Mike Pennington, CC BY SA 2.0)
Guest Post by Jonatan Marquez

The Crux

The rate at which species and populations have been going extinct in the last couple of centuries has well and truly earned the title of the planet’s sixth mass extinction event. However, most people rarely realize the severity of the situation. Hearing about the loss of two vertebrate species a year or having the last of some far-off species die out doesn’t see to cause much concern in the general public.

A species extinction is always preceded by population declines and extinctions. Perhaps highlighting the state of natural communities at this level might put the severity of the situation in better context. For example, the Living Planet Index (LPI) estimates that between 1970 and 2012, wildlife abundance has decreased by 58%. This paper focuses on the state and trends of populations of vertebrates by analysing i) the proportion undergoing declines or shrinkages, ii) the global distribution of population reduction events and iii) the general scale of population declines among mammal populations.

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Population Trends in the Face of Climate Change

Rapid warming is associated with population decline among terrestrial birds and mammals globally (2018) Spooner et al., Global Change Biology DOI: 10.1111/gcb.14361

The Indian Pond Heron, one species which could face population declines as a result of climate change
The Indian Pond Heron, one species which could face population declines as a result of climate change (Image Credit: Dr Raju Kasambe CC A-S 4.0)

The Crux

The term climate change is almost ubiquitous these days. Humans tend to concentrate on how the warming of certain parts of the globe will affect them, but the species we share the globe with also experience a myriad of effects at the hands of climate change. These include rising temperatures constricting the ranges of some species and concurrently extending the range of others, who can move into areas that were previously too cold for them.

Whilst the focus of climate change has often been on species range shifts, the effects on species abundances are less well studied. This paper attempts to quantify the effects of climate change on a large number of bird and mammal species, whilst accounting for other factors which could affect species abundances, like rates of land use by humans, species body size, and whether or not the animals are in a protected area.

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Scared to Death

Fear and lethality in snowshoe hares: the deadly effects of non-consumptive predation risk (2018) MacLeod et al., Oikos 127(3)

Fear itself of a predator is enough to reduce populations of a snowshoe hare, show Macleod at al.
Fear itself of a predator is enough to reduce populations of a snowshoe hare, show Macleod at al. (Image Credit: Dave Doe, CC BY 2.0)

The Crux

When we think of a predator-prey relationship, many colorful examples of charismatic animals come to mind: the lion and the wildebeest, the orca and the seal, the owl and the mouse. We think of these organisms locked in an endless battle, with one needing to catch and eat, the other to escape and live. While these are definitely interesting and important aspects of the predator-prey relationship, prey species need to worry about more than just being eaten. These “non-consumptive effects” play into what is called the Ecology of Fear.

This study was an attempt to show that the perceived risk of predation itself was enough to reduce survival in prey species. Unlike previous studies on this question, MacLeod et al. were the first to conclusively show this effect in mammals.

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