Quantifying the Effect of an Invader

Nest predation by raccoon dog Nyctereutes procyonoides in the archipelago of Northern Sweden (2018) Dahl & Åhlen, Biological Invasions, https://doi.org/10.1007/s10530-018-1855-4

The Raccoon Dog, an alien species, has made its way to Sweden recently. But what sort of effect does it have on the native fauna? (Image Credit: Prue Simmons, CC BY 2.0)

The Crux

We’ve spoken about biological invasions at length on EcolMass, and the detrimental effects that the arrival of a new species can have on native populations. Yet eradication is often impossible, and management expensive, so before taking extensive action, it’s always important to ensure that an alien species IS having a negative effect.

The raccoon dog is an Asian species, closely related to foxes, that was introduced to Europe in the early 20th century and has since spread into Scandinavia. Voracious predators that could spread further north due to climate change, our paper this week looks at the extent of their impact on the ecosystems they’ve spread to.

Century-long ecological time series? No problem

Guest post by Anders Kolstad

Herbarium specimens reveal increased herbivory over the past century (2018) Meineke et al, Journal of Ecology, DOI: https://doi.org/10.1002/ecs2.1276

Blueberry (Vaccinium angustifolium) has been subjected to increasing levels of chewing herbivory last 112 years. This remarkable conclusion was made possible by studying 215 physical specimens of this species preserved in a university herbarium (Image Credit: DLadek, CC0)

The Crux

Herbivory by insects has an important impact on plant life, but in light of the changing climate there have been few studies on corresponding changes in interactions between insects and plants. Today’s paper investigates changes in herbivory on leaves over the last century. How did they manage to analyse this? By using herbarium specimens. We’ve talked a little on EcolMass in the past on the importance of museum collections in ecology, and this is a fantastic example.

Species Associations in a Changing World

Using joint species distribution models for evaluating how species-to-species associations depend on the environmental context (2017) Tikhonov et al, Methods in Ecology and Evolution, DOI: https://doi.org/10.1111/2041-210X.12723

Species associations will change as the climate rises. So how can we attempt to predict these changes (Image Credit: Charles J Sharp, CC BY-SA 4.0)

The Crux

Statistical modelling is a crucial part of ecology. Being able to provide an (admittedly simplified) mathematical description of the relationship between species abundance, range or density and the surrounding environment is a huge help in taking proactive steps to manage an ecosystem, or predicting species numbers in other areas.

Historically models have used environmental variables to explain population or evolutionary developments in species. When modelling a single species, many ecologists have taken into account that the presence of other species (for example competitors or predators) may influence the presence of this single species. This has led to the rise of joint species distribution models (JSDMs), which take into account environmental variables, as well as the interactions between certain species. These models have become increasingly useful, and with environmental change now being the norm in many ecosystems, this week’s authors produced one such model that accounts for changes in species interactions in the face of changing environmental factors.

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 (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.

Why Defining Biodiversity Matters in an Ecosystem

Biotic homogenization can decrease landscape/scale forest multifunctionality (2016) von der Plas et al., Proceedings of the National Academy of Sciences of the United States of America, 113

Forests such as Białowieska in Poland perform a wide range of functions, but if its biodiversity rises, how will this change? (Image Credit: Jacek Karczmarz, CC A 3.0)

The Crux

Any ecosystem performs a multitude of functions, benefiting both the species that live in it and the humans who interact with it, from litter decomposition to resistance of drought to timber production. As such, maintaining high levels of ecosystems is a well-studied concept, and it has been posited that high levels of biodiversity increase the levels functions an ecosystem can perform, or its multifunctionality.

But while the word biodiversity is recklessly bandied about these days, scientifically it’s a somewhat vague term. At an ecosystem level, you may have patches of very high local (or alpha) diversity, but the turnover of species between patches (beta diversity) might be quite low. The variation in types of biodiversity may influence your ecosystem multifunctionality. For instance, patches of high alpha diversity might lead to high levels of functionality in some patches, but little functionality elsewhere, whereas high levels of beta diversity may lead to low levels of functionality, but many functions. This paper investigates relationships between different biodiversity levels and ecosystem multifunctionality.

Whom to Blame – Cats or Rats?

Trophic roles of black rats and seabird impacts on tropical islands: Mesopredator release or hyperpredation? (2015) Ringler et al., Biological Conservation, 185.

Feral cats are responsible for the decline of many endemic species worldwide. But will removing them boost rat populations, causing more potential harm? (Image Credit: Brisbane City Council, CC A 2.0)

Guest post by Bart Peeters

THE CRUX

For centuries, rats have been portrayed as carriers of diseases and death; whereas our feline friends, worshipped by the ancient Egyptians, will definitely make your YouTube video go viral (a quick Google search of “cat video” shows 1 310 000 000 results). Both have been introduced, either accidentally or deliberately, to islands where endemic species have evolved and adapted to an environment without these generalist predators. So how do you know if eradicating one of them will make things better for the native wildlife?

Before taking radical conservation actions, it may be a good idea to understand how feral cats (the apex predator), rats (the mesopredator) and their common prey are affecting each other. Namely, if you kill all the cats, will there be more rats to prey on seabirds? On the other hand, will killing all the rats really reduce the predation by cats on seabirds?

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 (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.

Finding the Key to Reef Shark Conservation

Reef accessibility impairs the protection of sharks (2018) Juhel et al., Journal of Applied Ecology 55

Species such as this Carribean reef shark have higher extinction risks than most fish. But how effective are our management efforts? (Image Credit: Wikipedia Commons)

The Crux

The importance of sharks goes well beyond what Jaws did to Hollywood, or one week in the USA each July. In any reef ecosystem, sharks perform a key functional role, exerting top-down pressure, stabilising food webs, and improving general ecosystem functioning. They’re also ‘charismatic’ species, meaning they’re easier to raise funding for, and bring money in through tourism. Yet pressure from fishing suggests that reef shark populations may be under threat, and with high body sizes and long lifespans, their populations are more sensitive than most to overfishing, making extinction risks higher.

Yet the lack of data on shark populations means that the effectiveness of the few existing management programs is largely untested. This paper looks at Marine Protected Areas (MPAs), areas in which national or international bodies prevent fishing or even entry, to see whether or not they are an effective conservation method for shark populations.

Bringing Back the Wolverine

Paying for an Endangered Predator Leads to Population Recovery (2015) Persson et al., Conservation Letters 8(5)

The Swedish government changed tactics at the end of the 20th century, giving incentives to farmers when there were successful wolverine reproductions in their area (Image Credit: Wikipedia Commons)

The Crux

Humans have a long history of driving dangerous predators out of their backyard. Wolves and wolverines have been driven out of different parts of Europe at different points in history at the behest of farmers looking to protect their livelihood, and the Tasmanian Tiger was driven to extinction for the same reason. But with the realisation that these predators bring enormous ecosystem benefits, governments have been searching for ways to bring about co-existence between predators and locals.

This study looks at a scheme introduced by a Swedish government in 1996, where reindeer herders had previously been compensated for any wolverine related losses. The new scheme introduced compensation for successful wolverine reproductions in the area. Persson et al. decided to have a look at how it fared.

Lessons From a Long History of Fish Invasions

Transport pathways shape the biogeography of alien freshwater fishes in Australia (2018), Garcia-Diaz et al., Biodiversity Research, DOI: 10.1111/ddi.12777

The European Perch, brought for angling by earlier settlers, has had severe effects on a number of native Australian fish (Image Credit: Wikipedia Commons)

The Crux

Invasive species are a problem in every type of ecosystem, be it by reduction of local diversity, or negative effects on a region’s economy or human health. Freshwater rivers and lakes are no exceptions to this. Invasive fish have impacts on local habitats which include outcompeting or just flat out eating local species, changing a habitat’s entire structure (say by clearing away aquatic vegetation or increasing pH levels) and the reorganisation of the entire population of a lake or river, from the birds that nest on the shoreline to the tiny planktonic species that are the base food source of the entire ecosystem. Once an invasive species is established, it can be impossible to remove.

So naturally, understanding where and how invasive species are likely to strike is of huge benefit. This paper tries to map that out, using Australia as a case study. It’s a great example; Australia has a long history with invasive species, and this study alone looks at 33 different types of invasive fish.