The Week in Science (1/19/2017)

Highlights from science news from the week of January the 19th, 2017.

Iceburg in Greenland. Getty.

Record High Temperatures Recorded in 2017. Photo: Getty.


New species of moth names for Donald Trump’s hair: http://goo.gl/news/FnfRk

How do local peoples experience climate change? Arctic warming has real impacts, today. http://goo.gl/news/z5wxt

Asteroid mining, one of the ways that the private sector space industry might see a boost, gets its first real target asteroid. http://goo.gl/news/7Lc2O

SpaceX Achieves Rocket Launch/Landing Success

SpaceX breaks out of its rocket-exploding-slump by successfully launching and landing the company’s Falcon-9 rocket. This success keeps SpaceX on track for its manned missions next year, but the pressure remains high as the stakes increase. Will SpaceX be able to provide a reliable space transport vehicle for the United States? We’ll be tracking this story as it progresses. http://goo.gl/news/q7erh

Scientific Expertise in Politics (or lack thereof)

This is a great example of where we need more people with scientific expertise in politics. Unfortunately, we have to rely on elected officials that have little to no understanding of the science, and so can’t really make effective policy decisions (given they are more likely to ignore input from the scientific community than someone with a science background). http://goo.gl/news/pfz5O

Primate Mass Extinction

60% of primates face extinction, mostly due to habitat loss. Climate change is one of the number one contributing factors to habitat loss, behind human development. The sooner politicians on both sides accept the reality of this, the sooner we can prevent the loss of humanity’s closest relatives on Earth. http://goo.gl/news/8ZHd3

Curiosity Rover Finds “Mud Cracks”

“Mud cracks” on Mars suggest liquid water present more recently than thought, or more to be understood about the surface erosion processes of the Martian surface. Either way, it’s exciting news from the Curiosity Rover. http://goo.gl/news/uAt72

NASA Preps for 8 Month Isolation Experiment

NASA prepares for its Mars mission by creating an isolation dome on a remote Hawaiian volcano. The participants will spend 8 months in isolation to simulate living on Mars (including a realistic 20 minute communications delay). The team will be resupplied using robots and entertainment will include a virtual reality system to simulate familiar and comfortable settings. Bets of luck! http://wpo.st/9rvS2

Antarctic Prepares to Shed 100 km+ Long Iceburg

A piece of ice in the Antarctic is poised to separate from the mainland – creating an iceburg 1/4th the size of Wales. That’s about a 100 km x 50 km rectangular chunk of ice for people that don’t know how big Wales is (I didn’t either). http://goo.gl/news/gAegQ

Oceans Around the World – The Sunda and Sahul Shelves

Notes on several key papers regarding biodiversity hotspots in and around the Sunda Shelf.

Article 1: Crandall 2008

Vicariance patterns as a result of Pleistocene sea-level changes in the Sunda Shelf area should be present in both invertebrates and their ectosymbionts. Highly variable results across many different studies have spurred the authors to explore a more closely linked hypothesis: That patterns of genetic variation found in marine invertebrates (in this case, two seastars) should closely match that of their ectosymbionts (a mollusk and crustacean). Most of the four species did show at least some genetic structure, but it was not concordant across species, with each species displaying a different pattern of range expansion most likely due to differences in dispersal, and adult survivability.

Source: https://www.ncbi.nlm.nih.gov/pubmed/19067797

Map of Sunda and Sahul.

Map of Sunda and Sahul. CC 3.0 By Maximilian Dörrbecker (Chumwa). Wikimedia Commons.

Article 2: Crandall 2012

Sea-level changes during the end of the Last Glacial Maximum (LGM) should correspond closely with population range expansions of marine species. Prior to sea-level rises, the Sunda shelf and neighboring shelves were well above the ocean. Beginning roughly 20,000 years ago sea-levels began to rise rapidly, covering the Sunda shelf under water and facilitating the rapid expansion of marine species into this new habitat. The authors suggest that since the genetic signal of this sea-level rise is present in so many species, this event can be used as a means of calibrating the heterogeneous rate of mutation rates of lineages through time, that is, that younger lineages tend to have higher mutation rates. The authors proclaim strong support for the idea of time dependency of molecular clocks. This is an important understanding because correlating the time of geologic events with species/population events is a critical aspect of marine phylogeography.

http://mbe.oxfordjournals.org/content/early/2011/11/17/molbev.msr227

Article 3: Kraus 2012

Here the authors investigate a genus of freshwater crab, Parathelphusa, for its historical biogeographic distributions in the Sunda region and the relation of those distributions to Pleistocene sea-level changes. The authors suggest that if Pleistocene-aged sea-level changes are responsible for the diversification of Parathelphusa clades throughout the Sunda region, then the rate of speciation should have greatly increased during that time. However, the authors find that most clades have Miocene or Pliocene origins, all with origins from Borneo although some speciation events did occur during the end of the Pleistocene, although rarely and via sporadic dispersal events as there have been no recent land-bridge connections.

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2699.2012.02771.x/full

Undergraduate Thesis: Effects of Artificial Moonlight on the Foraging Behavior of Mojave Desert Rodents

Effects of Artificial Moonlight on the Foraging Behavior of Mojave Desert Rodents

An Undergraduate Thesis Project
By Bryan White
03/25/2011

Abstract

Desert rodent communities are extremely diverse, which has prompted researchers to ask how so many species can coexist on similar, limited resources. Differences in foraging preferences associated with predator avoidance may contribute to coexistence. I determined how the foraging behavior of Mojave Desert rodents, especially pocket mice (Chaetodipus), were influenced by the increase in perceived predation risk associated with moonlight, which I simulated using artificial illumination. Millet (6.00 g) was mixed into trays filled with 2 L of pre-sifted sand. Seed trays were placed at stations located at different distances (2-82 m) from Coleman camping lanterns, and in either open or shrub microhabitats, so that rodents could choose to forage from resource patches with different levels of perceived risk. I also live-trapped rodents to identify likely foragers near the lanterns, and to determine the diversity and abundance of rodents in the area. Background illumination levels were recorded with using a Lux meter. I predicted that the amount of seeds removed would be highest at seed trays farthest from lanterns and under shrubs, and lowest at stations closest to lanterns and in open microhabitats. Surprisingly, I found no effect of distance, microhabitat, or illumination level on the amount of seeds removed by rodents.

Merriam's Kangaroo Rat

Merriam’s Kangaroo Rat. Photo CC 4.0 By Bcexp. Wikimedia Commons.

Introduction

Desert rodents are intriguing animals because of their ability to survive in extremely harsh climates where resources are limited. Desert rodent communities are extremely diverse, which has prompted researchers to ask how so many species can coexist on the same resources, seeds (Brown 1988). In the Mojave Desert, for example, six different genera (Ammospermophilus, Chaetodipus, Dipodomys, Neotoma, Onychomys, Perognathus, Peromyscus), representing three rodent families (Heteromyidae, Muridae, Sciuridae) can all be captured in roughly the same area (Stevens et al. 2009). Most explanations suggest that animals reduce competition via resource partitioning, but differences in predator avoidance abilities may also contribute to coexistence (Kotler 1984).

It is widely accepted that desert rodents differ in their microhabitat preferences, and that these preferences reflect differences in the ability of rodents to detect and avoid predators, including owls, mammalian carnivores, and snakes. For example, quadrupedal rodents such as pocket mice (Chaetodipus, Perognathus), tend to forage in the cover of large shrubs, whereas bipedal rodents such as kangaroo rats (Dipodomys) are often found in open microhabitats between shrubs (Kotler 1984). Kangaroo rats are adapted to forage in open microhabitats in which there is little cover from visual predators (Thompson 1982; Kotler 1984). These adaptations include hopping locomotion, the ability to hear very low frequency sounds (1-3 kHz), and dorsally located eyes that should aid in spotting predators (Thompson 1982; Kotler 1984). Predation rates on rodents by owls are higher both in open microhabitats and (in a separate experiment) during periods of full moon, when levels of illumination might make movements more conspicuous (Kotler 1988). In contrast, pocket mice lack these morphological specializations, but presumably can move more efficiently beneath the denser shrub canopy (Thompson 1982). Interestingly, owls and rattlesnakes, the two most important rodent predators in the Mojave Desert, may have different effects on microhabitat use by rodents. Owls directly affect the perception of risk by desert rodents (Kotler 1988), which is higher in open microhabitats (Brown et al. 1988). The presence of rattlesnakes, which tend to hide near shrubs to wait for prey and to avoid being eaten themselves, decreased foraging of kangaroo rats in shrub microhabitats, although only during summer, when snakes are active (Bouskila 1995).

Mojave desert rattlesnake

Mojave Green Rattlesnake. Predator of Kangaroo rats. Public Domain By Lvthn13. Wikimedia Commons.

The response of rodents to predation risk has traditionally been measured in 2 ways: analysis of microhabitat characteristics at locations where rodents are captured, and foraging experiments to estimate differences in seed removal rates associated with different microhabitats. Optimal foraging theory states that animals will forage in an area until the costs of continued foraging, including perceived predation risk, outweigh the benefits (Morris 1997). The giving-up density (GUD), the density of seeds remaining in an artificial seed patch after a foraging bout, reflects this quitting harvest rate, and thus provides an index of an animal’s perceived risk and foraging costs associated with particular microhabitats (Brown et al. 1988). Both methods have been used to study how moonlight intensity affects rodent activity. Kotler (1984) found that increased illumination, simulated by camping lanterns, decreased captures in open microhabitats for some species and shifted habitat use for others in the Great Basin. Others have reported that bright moonlight reduces overall rodent activity aboveground (Brown et al. 1988).

I modified Kotler’s (1984) approach to investigate the possible effects of artificial illumination on foraging behavior of rodents in shrub and open microhabitats in the Mojave Desert. Rather than studying shifts in captures in different microhabitats, I measured seed removal rates in artificial seed trays placed at different distances from an artificial light source, a gas-powered Coleman lantern. I also quantified variation in light levels at varying distances from the lantern and in the open and beneath shrubs to understand better how actual light levels differ between these microhabitats. I predicted that seed removal rates would be lower (and GUDs higher) in trays close to the lanterns, where illumination was greatest, than at trays where there was only natural light. I also expected that rodents would remove relatively more seeds from trays beneath shrubs than in open microhabitats, especially near the lanterns, where the difference in illumination would be greatest.

Methods

My study site was conducted approximately 5 km NW of the Desert Studies Center, Zzyzx, California, during the months of June and July 2010. The site was a broadly sloping bajada at the base of an alluvial fan. Vegetation consisted mostly of creosote bush (Larrea tridentata), burrobush (Ambrosia dumosa) and desert holly (Atriplex hymenelytra), with scattered forbs and grasses. The substrate was a mixture of medium-size to small rocks and gravel, with some sandy washes. Shrub microhabitats were considered to be any shrub that appeared large enough to provide adequate canopy cover over a seed tray. Open microhabitats were locations that were at least 1 m from shrubs.

Creosote bush, Mojave Desert

Creosote bush, Mojave Desert. Public Domain By Klokeid. Wikimedia Commons.

To determine which rodent species were present at my site and foraging in seed trays, I set large Sherman live traps on the night prior to foraging trials. Traps were baited with commercial bird seed that had been microwaved for 5 min to prevent germination. During June, 30 traps were placed at same locations as the seed trays. During July, trapping was done in a 7 x 7 grid (49 traps separated by 10 m) in the area where seed trays were placed.

Artificial seed trays were houseplant saucers (6 cm deep and 32.5 cm in diameter) buried so that edges were flush with the ground. When set, each tray contained 6.00 g of millet mixed in 2 L of pre-sifted, fine sand. In June, I placed trays 2, 12 and 22 m points along 2 parallel lines extending out from a central Coleman (Dual Fuel) camping lantern. This was repeated 3 times at 50-m intervals, for a total of 30 trays. In July, I placed 32 trays from (2 m to 72 m at 10 m increments) in four different directions extending out from two centrally-placed lanterns. Two lanterns were used in the second design in an attempt to increase illumination levels. At a given location, seed trays were randomly assigned to be either in a shrub or open microhabitat. One additional tray was covered with hardware cloth to prevent foraging and was used as a control to quantify changes in weight of seeds due to moisture overnight (Stapp and Lindquist 2007).

Trays were set out at dusk. I allowed rodents to forage in seed trays for approximately 4 h. The remaining seeds and sand were collected from trays and taken back to the Desert Studies Center lab, where the sand was sifted to remove seeds. The seed was cleared of debris and weighed using a precision scale to estimate the amount of seeds removed. Seed trays were considered to have been foraged if the amount of seed removed differed by 2% of control trays from that night.

At the beginning of each foraging trial, I measured light intensity using an Extech 401036 light meter. Illumination was measured by placing the light meter on the seed tray so that the light receptor faced straight up. This measured the ambient light in the area, as opposed to the relative intensity that a rodent may perceive being emitted from a light source (either the moon and stars or lantern). I assumed that rodents look to their immediate surroundings, rather than some distant light source, to decide the relative risk of the potential foraging patches. Trials were conducted under similar background moon conditions (waxing gibbous).

All statistical analyses were conducted in Microsoft Excel (2007) Data Analysis Toolpack and Minitab 15 (Minitab Inc. 2007).

Results

Based on a total trapping effort of 64-trap-nights over the 2 trapping sessions, pocket mice Chaetodipus (17 individuals of 2 species, C. penicellatus, C. formosus, that were not distinguished) were the most abundant rodents, followed by Merriam’s kangaroo rat (D. merriami, 6 individuals) and the desert woodrat (Neotoma lepida, 1 individual). I therefore assumed that most trays were visited by pocket mice.

A total of 62 seed trays were set out during the 2 trials. During the June trials, 3 of 30 trays (1 shrub, 2 open, 1 spilled) were considered to have not been foraged, whereas in July, more than 2/3 (22/32) of the trays were not foraged (10 shrub, 12 open, 1 spilled). Only results from seed trays that were considered foraged were included in the analysis. Combining across all distances and trials, there was no significant difference in the amount of seeds removed in shrub and open microhabitats during June or July (Fig.1; P > 0.05). Combining both trials, the amount of seed removed was not related to distance from the lanterns in either open (Fig. 2; R2 = 0.007, P = 0.745, DF = 15) or shrub (Fig. 2; R2 = 0.15, P = 0.0936, DF = 18) microhabitats.

Illumination levels were highest in seeds trays near the lanterns, but declined considerably by 12 m from the lanterns (Fig. 3). Shrub and open trays were exposed to similar light levels.

Surprisingly, illumination did not influence seed removal rate in the way that I predicted. At all levels of illumination and in both shrub and open microhabitats, rodents consumed most of the seeds in the trays (Fig. 4). In fact, the amount of seeds removed was lowest and most variable at the lowest light intensities.

Discussion

I found no evidence to support my hypothesis that rodents would spend more time foraging in darker, shrub microhabitats, where risk of predation would presumably be lower. This was particularly surprising because pocket mice were the most common rodents I captured at my study sites and probably were responsible for most of the foraging in seed trays. Pocket mice are quadrupedal and generally prefer the cover of shrubs (Kotler 1988), and therefore would be expected to be sensitive to predation risk. My results differ from those of Kotler (1984), who found, based on live-trapping, that rodents, including quadrupedal species, increased their use of shrub microhabitats in the presence of artificial illumination. However, Kotler (1984) also found that seed enrichments increased the use of the open microhabitat by kangaroo rats. This suggests that, in my study, while pocket mice may have focused their foraging efforts on removing seeds from under shrubs, kangaroo rats may have been opportunistically foraging in brighter areas, and due to its larger body size and bipedal locomotion, consistently removed large amounts of seeds from those trays.

The fact that rodents ate nearly all the seeds in seed trays at all distances from the lanterns and irrespective of illumination levels suggests that the bright light associated with the lanterns did not deter them from foraging. In fact, rodents removed the smallest amounts of seed in trays at the darkest light levels, including some beneath shrubs (Fig. 4). This suggests that factors other than illumination and microhabitat influenced foraging behavior at these low light levels. It also suggests that rodents can find a large amount of dispersed seed (6 g) in a relatively short time. It is possible that multiple rodents visited a given tray, but I was not able to determine the number of rodents using each tray.

If I were to repeat this study, I would increase the number of replicate seed trays and use the same experimental design throughout. I also would keep a record of whether there are tracks in trays as an index of foraging. Another way to improve my experimental design would be to video record seed trays to know how many animals and of which species visited a seed tray during a foraging bout.

Literature Cited

Bouskila, A. (1995). Interactions between predation risk and competition: A field study of kangaroo rats and snakes. Ecology, 76(1), 165-178.

Brown, J. S., Kotler, B. P., Smith, R. J., & Wirthz, W. O.,II. (1988). The effects of owl predation on the foraging behavior of heteromyid rodents. Oecologia, 76(3), 408-415.

Kotler, B. P. (1984). Risk of predation and the structure of desert rodent communities. Ecology, 65(3), 689-701.

Kotler, B. P. (1988). Environmental heterogeneity and the coexistence of desert rodents. Annual Review of Ecology and Systematics, 19, 281-307.

Morris, D. W. (1997). Optimally foraging deer mice in prairie mosaics: A test of habitat theory and absence of landscape effects. Oikos, 80(1), 31-42.

Stevens, R. D., & Tello, J. S. (2009). Micro- and macrohabitat associations in mojave desert rodent communities. Journal of Mammalogy, 90(2), 388-403.

Stapp, P. and Lindquist, M (2007). Roadside foraging by kangaroo rats in a grazed short-grass prairie landscape. Western North American Naturalist, 67(3), 368-377.

Thompson, S. D. (1982). Microhabitat utilization and foraging behavior of bipedal and quadrupedal heteromyid rodents. Ecology, 63(5), 1303-1312.