Human impacts on ecosystems

Pet dogs living with humans have infected African lions with distemper virus, while people are putting pumas off their lunch...
26 January 2015

Interview with 

Dr Mafalda Viana, Glasgow University, Justine Smith, University of California


Humans don't have a good track record when it comes to preserving the delicate Lion (Panthera leo) lying down in Namibia.balance of nature, and Khalil Thirlaway has been looking at two recent examples of how our presence can have unforeseen - and unfortunate - consequences for the ecosystem...

Khalil - One of the reasons that humans have become the dominant species on our planet is our ability to colonise all sorts of habitats - from wet to dry, cold to hot and high to low. We even change the environment to suit our needs, sculpting the land to build and farm on it. As our population grows, it inevitably leads to us bumping up against the local wildlife which can have complex and far-reaching consequences, including diseases spreading to humans from wild animal populations, as was the case with Ebola. But this is a two-way street and two papers published this week show how human presence can spread diseases among wild animals and also alter animals' behaviour. In Tanzania, dogs are implicated in an outbreak of canine distemper virus that wiped out nearly a third of the lions in the Serengeti National Park as Mafalda Viana of Glasgow University explains...

Mafalda - At that time, we didn't know exactly what was the cause but because distemper virus is a disease typically associated with domestic dogs, it was believed that it was these dogs that live in the villages around the natural park that transmitted the infection into the lions. So, at that time, around '96, there was a vaccination programme that started to vaccinate the dogs in order to not only protect the dogs but also trying to prevent infection into the natural park.

Khalil - But there have nonetheless been several outbreaks of distemper virus in the Serengeti lion since. Were dogs still the cause?

Mafalda - In the beginning, it seems that the domestic dogs could've been responsible for transmitting this disease into the lions. But since the mid '90s, we saw a change in these dynamics, meaning that the infection that would occur in the lions were no longer exclusively related to those happening in the dogs. And so, what it suggests is that the dogs are not the only [species] responsible for transmission to the lions and that there's probably wildlife species inside the park themselves, in addition to the lions, that are maintaining the disease and causing these sporadic outbreaks.

Khalil - But could this have been avoided?

Mafalda - Humans do need to live somewhere and unfortunately frequently creates these human-wildlife conflicts, but hopefully we can find ways of balancing the two.

Khalil - Through vaccination, it's possible to prevent our domestic animals from becoming a reservoir for infection, both to us and local wildlife. But coughs and sneezes are not the only way that human habitation can affect the ecosystem. A team from the University of California Santa Cruz have been studying how housing in and around the mountains of the San Francisco Bay Area is affecting the behaviour of another top predator: the puma, or mountain lion. Pumas hunt large prey such as deer and will often keep returning to a kill to feed for a number of days. Normally, they don't stray far from their prize but if they don't feel safe, they'll often retreat until the cover of darkness. Justine Smith...

Justine - A lot of places in our mountain range where we work are these low-density residential areas where houses are maybe 50 to 100 meters apart and pumas are still using that part of the landscape to hunt and do all sorts of things. When they're near houses, they move far away during the day and sleep somewhere else and come back only at night to feed. And so, these animals are able to hunt right up against people's homes, but they just won't hang around when they feel disturbed.

Khalil - All those trekking back and forth waste valuable energy and combined with the loss of food to scavengers while they're away means that they need to kill more deer just to survive. This puts an increased pressure on the deer population in these areas.

Justine - Here, what we're seeing is really that the humans are sort of the behavioural top predator, if you will, that's changing the feeding behaviour of the natural top predator which is the puma.

Khalil - But there are ways to limit the impact with moves towards more clumped housing development which can be segregated from the puma's habitat, along with other measures to minimise the impact of our daily lives on theirs.

Justine - There has been a lot of attention in the development and planning world recently to look at more conservation planning when we think about designing new areas for development. In terms of places that are already developed there are a number of potential options that could help: constraints on what the kind of light bulbs are there, how strong lights can be, sound ordinances might help to mediate disturbances to animals.


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