For the last year I have been walking around Las Vegas every day with my camera for exercise and to avoid going mental. Over that time period I have accumulated a collection of lizard photos which I thought would make a nice post. Even though there are lots of little lizards in the Mohave desert (more than 20 species), even in the urban landscape of Las Vegas, most photos are fortuitous since they are so quick and usually small. Lizards and iguanas both belong to the reptile group of vertebrates. The Squamata, or the scaled reptiles, are the largest recent order of reptiles, comprising all lizards and snakes. Iguanas are actually a type of lizard. Therefore, they are not very different from lizards in many aspects. However, they are different from most lizard species in several ways including their colors and the foods they eat. Many lizard species are insectivorous. They like eating insects such as cockroaches, crickets, ants, and beetles. Many lizard species are also omnivorous; they eat just about everything including insects, carrion, small tetrapods, spiders, fruits, and vegetables. Iguanas tend to be herbivores. Of the many species of swifts and spiny lizards, 22 species, some with several subspecies, occur in the United States. Others are found southward through Mexico to northern Panama. In the United States, the lizards of this group are found from southern New York, southern South Dakota and northern Washington in the north, to South Florida, the Gulf States and the Mexican border. Several of the fence lizards (which, because of their rapid movements, are colloquially referred to as “swifts”) are familiar backyard species. Others, among them the bunchgrass lizards and Yarrow’s spiny lizard, are denizens of remote montane fastnesses. Like many other lizards, spiny lizards exhibit metachromatism, which is color change as a function of temperature. When it is cooler, colors are much darker than when the temperature is high. Darker colors increase the amount of heat absorbed from the sun and lighter colors reflect solar radiation.
This is the final post in my series on photosynthesis in Mohave desert plants. While green leaves are commonly considered as the primary sources of photosynthesis, higher plants can potentially use almost all vegetative and reproductive structures to perform carbon fixation. Chlorophyll-containing bark and wood tissue, most fruit, root and fertile flower organs typically perform an effective internal CO2 recycling using the respiratory released CO2. Photosynthetic stems have positive effects on the carbon economy of plants through two main mechanisms. Photosynthetic stems can either assimilate atmospheric CO2 and contribute to the net carbon gain of the plant through the process of stem net photosynthesis, or decrease respiratory losses by recycling CO2 previously respired by roots and stems through the process of stem recycling photosynthesis.Plants with green stems are categorized by one of three types of stem photosynthesis syndromes. Retamoids include leafless or almost leafless woody plants that have stomata in the stem epidermis allowing for gas exchange with the atmosphere (Schaedle 1975). Another type of photosynthetic stems are the succulent pachycauls or the sarcocaulescent group, which has large-sized stems with translucent exfoliating bark, a large amount of parenchymatous tissue that serves as a water reservoir, and non-succulent, drought-deciduous leaves (Franco-Vizcaino et al.1990). An example of this would be the Boojum Tree (Fouquieria columnaris) and the related Ocotillo (Fouquieria splendens) as both lack stomata and recycle respiratory released CO2 to survive during drought. Another type of photosynthetic stem is found in cactus, which take up carbon dioxide at night with stoma using CAM photosynthesis. The inadequacy of the current state of knowledge for describing or understanding the diversity of structure, function, and ecological significance of photosynthetic stems suggest areas for further research. The diversity of taxonomic types, and classes of photosynthetic stems, results in a large diversity of structural characteristics. In this post, I have simply chosen interesting examples without resolving these difficulties. I have also decided to throw caution to the wind and use lots of technical jargon.
This is the third in a series of posts on carbon fixation in Mohave desert plants. In this post we will focus on plants that use CAM carbon fixation which includes cactus, yucca and agave. The most important benefit of CAM to plants is the ability to leave most leaf stomata closed during the day. Plants employing CAM are most common in arid environments, where water comes at a premium. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evaporation and transpiration, allowing such plants to grow in environments that would otherwise be far too dry. Plants using only C3 carbon fixation, for example, lose 97% of the water they take up through the roots to transpiration – a high cost avoided by plants able to employ CAM. The Mojave Desert is the northernmost “hot desert” in North America and essentially a transition land between the Great Basin and Sonoran. It’s the smallest of the Big Four, covering some 54,000 square miles of southeastern California, southern Nevada, and itty-bitty strips of southwestern Utah and northwestern Arizona. Roughly speaking, the Great Basin Desert yields to the Mojave at the northern range limit of creosote bush, the defining shrub of North America’s hot deserts; its distribution essentially outlines them. You can rightly think of it as the hot-desert equivalent of big sagebrush. But the trademark plant of the Mojave, the one whose geography basically maps out this desert, is the Joshua-Tree. This outsized yucca actually flourishes best on the Mojave margins, reaching peak development on middle slopes of foothills and bajadas. Interestingly, the Joshua-Tree uses C3 carbon fixation while most of the remaining yucca and agave use CAM carbon fixation, along with all of the cactus species.
This post is the second on my series on Mohave desert plants, this time focused on C4 plants, not really as complex as it might sound. The C4 photosynthetic pathway has evolved an estimated 45 times in terrestrial plants (Sage 2004), and is most prominent in grasses, which account for roughly 25% of global terrestrial primary production (Still et al. 2003) and include important crop and weed plants and potential biofuels such as maize, sugarcane, sorghum and switchgrass. The highest rate of photosynthesis is typically observed in C4 plants. The photosynthetic rate in such plants is known to be directly related with the variation of the solar rays in the daytime. Maximum rate of photosynthesis occurs in the red and blue regions of the visible light as seen in the absorption spectra of chlorophyll a and b. These are of economic importance as they have a comparatively higher photosynthetic efficiencies in comparison to other plants. C4 photosynthetic plants outperform C3 plants in hot and arid climates. By concentrating carbon dioxide around Rubisco C4 plants drastically reduce photorespiration. The frequency with which plants evolved C4 photosynthesis independently challenges researchers to unravel the genetic mechanisms underlying this convergent evolutionary switch. The conversion of C3 crops, such as rice, towards C4 photosynthesis is a long‐standing goal. Nevertheless, at the present time, in the age of synthetic biology, this still remains a monumental task, partially because the C4 carbon‐concentrating biochemical cycle spans two cell types and thus requires specialized anatomy.
Desert plants tend to look very different from plants native to other regions. They are often swollen, spiny, and have tiny leaves that are rarely bright green. A desert always has a limitation of water but the temperature may be hot or cold, high altitude and cloudy like parts of Costa Rica or low altitude and windy like the Cape Preserve in South Africa. The strange appearance of these plants is a result of their remarkable adaptations to the challenges of the desert climate. Desert plants have developed three main adaptive strategies with diverse implementations often in different species with convergent evolution to the same form: succulence, drought tolerance and drought avoidance in annual plants. Each of these is a different but effective suite of adaptations for prospering under conditions that would kill plants from other regions. These differences often extend to the cellular level with the development of special structures to store water in leaves and stems, the periodic shedding of leaves, and special adaptations to even the basic photosynthesis process. Chlorophyll (the green pigment in plants) is the only known substance in the universe that can capture volatile light energy and convert it into a stable form usable for biological processes (chemical energy) through the Calvin Cycle and the enzyme RuBisCO. Green plants use blue and red light energy to combine low-energy molecules (carbon dioxide and water) into high-energy molecules (carbohydrates or starch), which they accumulate and store as energy reserves. There are at least three variations of photosynthesis, all of which use the same basic mechanism, C3 carbon fixation used by most plants, C4 carbon fixation used in about 3% of plants and the CAM (crassulacean acid metabolism) carbon fixation pathway that evolved in plants like cactus as an adaptation to arid conditions.
Sometimes, looking for plants and flowers in winter can be interesting, particularly near a source of fresh water in the desert. In November, I visited Rogers and Blue Point Springs on the north shore of Lake Mead in the Lake Mead National Recreation Area. Rogers Spring and other springs in the “North Shore Complex” comprise one of the terminal discharge areas for the regional carbonate-rock aquifer system of eastern Nevada and western Utah. The source of the water to this spring and other regional carbonate-rock aquifer springs is uncertain. The prevailing theory suggests that much of the recharge water that enters the carbonate-rock aquifer occurs in the high mountain ranges around Ely, Nevada, located 250 miles north of Lake Mead. As this ground water flows south through the carbonate rocks, it encounters several faults along the way, including the Rogers Spring Fault, which has caused the older carbonate rocks (primarily limestone and dolomite) to be displaced against younger evaporite deposits of the Muddy Creek and Horse Spring formations. Here, the lower permeability of these evaporite deposits, along with high subsurface water pressure, forces the ground water in the carbonate rocks to flow upward along the fault and emerge at the surface as Rogers Spring.
The Company’s Garden is the oldest garden in South Africa, a park and heritage site located in central Cape Town. The garden was originally created in the 1650s by the region’s first European settlers and provided fertile ground to grow fresh produce to replenish ships rounding the Cape. It is watered from the Molteno Dam, which uses water from the springs on the lower slopes of Table Mountain. The Dutch East India Company established the garden in Cape Town for the purpose of providing fresh vegetables to the settlement as well as passing ships. Master gardener and free burgher Hendrik Boom prepared the first ground for sowing of seed on the 29th of April 1652. The settlers sowed different kinds of seeds and kept record thereof each day. Through trial and error they managed to compile a calendar which they used for the sowing and harvesting throughout the year. At first they grew salad herbs, peas, large beans, radish, beet, spinach, wheat, cabbage, asparagus and turnips among others. By 1653 the garden allowed the settlers to become self sustainable throughout the year.
The South African Ostrich (Struthio camelus australis), also known as the Black-Necked Ostrich, Cape Ostrich or Southern Ostrich is a subspecies of the common ostrich endemic to Southern Africa. In the 18th century, ostrich feathers were so popular in ladies’ fashion that they disappeared from all of North Africa. If not for ostrich farming, which began in 1838, the world’s largest bird would probably be extinct. Today, ostriches are farmed and hunted for feathers, skin, meat, eggs, and fat — which, in Somalia, is believed to cure AIDS and diabetes. Ostriches were hunted to extinction in the Middle East and might have met the same fate in Africa if not for the evolution of ostrich farms. Ostriches are now farmed commercially in more than 50 countries around the world, including the United States. In Roman times, there was a demand for common ostriches to use in venatio games or cooking. They have been hunted and farmed for their feathers, which at various times have been popular for ornamentation in fashionable clothing (such as hats during the 19th century). Their skins are valued for their leather. In the 18th century they were almost hunted to extinction; farming for feathers began in the 19th century. At the start of the 20th century there were over 700,000 birds in captivity. The market for feathers collapsed after World War I, but commercial farming for feathers and later for skins and meat became widespread during the 1970s. Common ostriches are so adaptable that they can be farmed in climates ranging from South Africa to Alaska.
Cape Point is in the Cape of Good Hope Nature Reserve within Table Mountain National Park, which forms part of the Cape Floral Region, a World Heritage Site. It includes the majestic Table Mountain chain, which stretches from Signal Hill to Cape Point, and the coastlines of the Cape Peninsula. This narrow stretch of land, dotted with beautiful valleys, bays and beaches, contains a mix of extraordinarily diverse and unique fauna and flora. The Cape Peninsula (around 470 sq km) has 2285 flowering plant species. Table Mountain National Park alone has 1470 of these. Mountain fynbos dominates the park. It’s characterised by four main groups: protea shrubs with large leaves (proteoids), fine-leaved shrubs (ericoids), wiry, reed-like plants (restioids) and bulbous herbs (geophytes). Table Mountain National Park includes the Cape of Good Hope and Cape Point. Although the Cape of Good Hope Nature Reserve (or Cape Point as it is colloquially called) occupies only 16% of the area of the Cape Peninsula as given by Adamson & Salter (1950), the flora of Cape Point comprises 41% of the flora of the whole Peninsula. This illustrates the fact that many of the habitats and plant communities of the Peninsula are represented at Cape Point. Cape Point is the windiest place in South Africa and experiences only 2% of all hours in the year with calm conditions. I also want to mention that all of the following photographs were taken in October, in the middle of spring in the Southern Hemisphere.
I thought that I would write an introductory post on the geography and history of the Cape Peninsula, mainly because while everyone has heard of Cape Town and the Cape of Good Hope, knowledge usually ends at recognition. The Cape Peninsula (Kaapse Skiereiland) is a rocky and hilly peninsula that juts out into the Atlantic Ocean at the south-western extremity of the African continent. At the southern end of the peninsula are Cape Point and the Cape of Good Hope. On the northern end is Table Mountain, overlooking Cape Town, South Africa. The peninsula is 32 miles (52 km) long from Mouille point in the north to Cape Point in the south. The Peninsula has been an island on and off for the past 5 million years, as sea levels fell and rose with the ice age and interglacial global warming cycles of, particularly, the Pleistocene. The last time that the Peninsula was an island was about 1.5 million years ago. Soon afterwards it was joined to the mainland by the emergence from the sea of the sandy area now known as the Cape Flats. The towns and villages of the Cape Peninsula and Cape Flats now form part of the City of Cape Town Metropolitan Municipality. One of the many reasons that travelers choose to visit Cape Town is its abundance of scenic beauty and natural attractions. The city itself is situated between the Atlantic Ocean and Table Mountain, one of the world’s Seven Wonders of Nature. Table Mountain’s iconic plateau forms the dramatic backdrop of the city and is a must-see for visitors. On the peninsula, there are beaches, penguins, seals, ostriches and lots of hiking trails with beautiful scenery. For me, the famous fynbos with it’s many plants and flowers were a major draw along with the history and all of the above.