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--- 2018:groups:g8:start [2017/12/18 14:39] – marquitti
+++ 2018:groups:g8:start [2024/01/09 18:45] (current) – external edit 127.0.0.1
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-<WRAP center round todo 60%>
+**Group 8**
-Option 1 below. Other options (ordered by difficulty) :
-**Plant defences limit herbivore population growth by changing predator–prey interactions.**
+====== Competition between brown bears and grey wolves ======
-Kersch-Becker et al 2017. Proceedings of the Royal Society B: Biological Sciences. 284: 20171120.
-[[http://rspb.royalsocietypublishing.org/content/royprsb/284/1862/20171120.full.pdf]]
-**Exposure to the leaf litter microbiome of healthy adults protects seedlings from pathogen damage.**
+Wiki site of the practical exercise of the [[http://www.ictp-saifr.org/mathbio7|VII Southern-Summer School on Mathematical Biology]].
-Christian et al 2017. Proceedings of the Royal Society B: Biological Sciences. 284: 20170641.
-[[http://rspb.royalsocietypublishing.org/content/royprsb/284/1858/20170641.full.pdf]]
-**Zika virus activates de novo and cross-reactive memory B cell responses in dengue-experienced donors**
+Here you will find the exercise assignment and the group's products.
-Rogers et al. 2017. Science Immunology. 2: eaan6809.
-[[http://immunology.sciencemag.org/content/2/14/eaan6809]]
-</WRAP>
-{{ :2018:groups:g8:721303_1outlife041516.jpg |}}
+If you are a group member login to edit this page, create new pages from it, and upload files.
-**Competition between apex predators? Brown bears decrease wolf kill rate on two continents.**
+===== Introduction =====
-Tallian et al. 2017. Proceedings of the Royal Society B: Biological Sciences. 284: 20162368.[[http://rspb.royalsocietypublishing.org/content/royprsb/284/1848/20162368.full.pdf]]
+Different apex predators may share the same resources in a given environment. For instance, the grey wolf and the brown bear are predators of ungulates in North America and Europe. Bears usually dominate scavenged prey, which motivates the common assumption that wolves have to hunt more in the presence of bears to compensate the loss of resources. Tallian et al. evaluated a long dataset to understand how the presence of bears affects the killing rate of wolves and found , unexpectedly, that the time between consecutive kills made by wolves increased in the presence of bears, in both sites. The authors suggest some mechanisms to explain this:
+  * bears reduce densities of neonate ungulates (i.e. exploitative competition)
+  * wolves take longer between kills by attacking larger preys or by feeding on usurped kills under bears' presence (i.e. interference competition and/or kleptoparasitism)
-**Abstract:** Trophic interactions are a fundamental topic in ecology, but we know little about how competition between apex predators affects predation, the mechanism driving top-down forcing in ecosystems. We used long-term datasets from Scandinavia (Europe) and Yellowstone National Park (North America) to evaluate how grey wolf (Canis lupus) kill rate was affected by a sympatric apex predator, the brown bear (Ursus arctos). We used kill interval (i.e. the number of days between consecutive ungulate kills) as a proxy of kill rate. Although brown bears can monopolize wolf kills, we found no support in either study system for the common assumption that they cause wolves to kill more often. On the contrary, our results showed the opposite effect. In Scandinavia, wolf packs sympatric with brown bears killed less often than allopatric packs during both spring (after bear den emergence) and summer. Similarly, the presence of bears at wolf-killed ungulates was associated with wolves killing less often during summer in Yellowstone. The consistency in results between the two systems suggests that brown bear presence actually reduces wolf kill rate. Our results suggest that the influence of predation on lower trophic levels may depend on the composition of predator communities.
+{{ :2018:groups:g8:721303_1outlife041516.jpg |}}
+© Stan Tekiela
+===== Assignment =====
-**Description:** Different apex predators may share the same resources in a giving environment. The grey wolf and the brown bear are predators of ungulates in North America and Europe. The authors evaluated a long dataset to understand how the presence of bears affects the  kill rate of wolves. Wolves increased the time between consecutive kills in bears’ presence in both sites. The authors suggest some mechanisms to explain this:
+Propose and analyze a simple mathematical model to describe the coupled dynamics of populations of wolves and bears, taking into account the possibility of quite distinct details about their interaction.
-  - bears reduce densities of neonate ungulates (i.e. exploitative competition)
-  - wolves delay by killing larger preys or feeding on usurped kills under bears' presence (i.e. interference competition + kleptoparasitism)
-**Proposed task:** Think about the balance of exploitative and interfere
+===== Questions and suggestions =====
-nce competition between bears and wolves. What are the negative and positive effects of bears to wolves’ kills? How bears can enhance the feeding of wolves? Think about considering the handling time differences in the absence and presence of bears.
-**Challenge:** The authors suggest that the presence of both predators possibly impact prey less than the sum of their individual impacts. Include prey’s population dynamic on the model considering the effect of the predators in sympatry and allopatry.
+  * Be careful about the distinctions between kill rate, consumption rate and population growth rate.
+  * Consider the difference, in this system, between exploitative and interference competition. How can bears increase the feeding rate of wolves? Do bears affect the handling time of wolves?
+  * Are there only negative effects of bears on wolves’ kills, or are positive effects possible? In that case, what would be the consequence for the populations dynamics?
+  * The authors suggest that the presence of both predators possibly impact prey less than the sum of their individual impacts. Does your model confirm that possibility under some circumstances?
+===== Reference =====
+**Competition between apex predators? Brown bears decrease wolf kill rate on two continents.**
+Tallian et al. 2017. Proceedings of the Royal Society B: Biological Sciences. 284: 20162368.[[http://rspb.royalsocietypublishing.org/content/royprsb/284/1848/20162368.full.pdf]]