Look at Them White Rhinos!

As it is fast approaching the end of term, I have more free time to browse around the web. Then I stumbled upon these precious photos on National Geograhic by Ed Yong. 

WWF announced 22nd September as the World Rhino Day in 2010. After killing of rhinos by poachers hit record high in 2012 in South Africa, these rhinos might be the last remaining ones as they might be extinct in the next decade.

Thought of the day: Are the economical and recreational values brought by poaching and/or hunting animals greater than the intrinsic value of our endangered species?

Invasive species - not human's fault?

Last week, I spoke about how humans have been responsible for the introduction of invasive species. On a second thought, there are other contributing factors to the spread of non-native species. Those factors indirectly push native species to their limits, and towards extinction. 

In 2011, EU raised concerns over threatened freshwater species. One of the major risks was alien species, they believed. However, there was little emphasis placed upon the direct introduction of these species by humans. Instead, invasive species, such as Chinese mitten crabs and Himalayan balsam were transferred through Europe's rivers. So, are humans not the source of trouble?

Reading into this - In fact, in the European coastal waters, 24.5% of non-indigenous species entered through the Suez canal. Only 9% of them was intentionally released. Occhipinti-Ambrogi laid out an important relationship between changes in the biosphere and development of invasive species. 

Stages in the development of an invasive non indigenous species. 

Note that the magnitude of the release of invasive species is greatly affected by climatic change. It interacts with non-indigenous species by altering the physical-chemical conditions (PCF) in relation to temperature and oceanographic characteristic. Then PCF contributes to the change of new communities patterns. As we are currently experiencing global warming, the warming of climate is a primary cause to physiological stress. This leads to mass mortalities in benthic organisms, especially those who were already near their tolerance limit. As a result, there will be empty niches for new colonisers (invasive species). 

Without getting distracted into the never-ending discussion of global warming, let's just focus on the complexity of invasive species and the route to extinction of native species. 

Certainly, non-native species play a critical role in driving native species out of where they were originated. From the previous blog, I mentioned how humans have intentionally introduced species to control another. However, the surge in invasive species very much depends on other factors too, such as global warming. But human activity is the main reason for rising CO2, hence the greenhouse effect?Although global warming can be blamed to have exacerbated the effect of invasive species, human is still the key underlying factor. 

Number of references found as evidence for each
mechanism and type of facilitation 

Despite all the negativities, some authors are determined to prove that invasive species do not only bring detrimental impact, like extinction. For instance, zebra mussels, as one of the invasive species, actually support up to 700% more taxa than neighbouring mussel-free habitat. Yellow perch also have higher growth rates as zebra mussel colonies provided increased availability of invertebrate prey. 

Turns out in certain circumstances, invasive species might actually have positive impacts on native species. 

Carry on from last blog, introduction of invasive species might not be entirely human's fault. Although it is one of the reasons behind the verge of extinction of many other species, on the other hand, it may actually have opposite effects, thereby facilitating positive interactions between no-native and native species. Not so hopeless after all? 

Human and Invasive Species

Small Indian Mongoose

Adorable? This Small Indian Mongoose was introduced to control rats in places such as Mauritius and Hawaii in late 1800s. Such efforts, however, have caused extinction of some endemic birds, reptiles and amphibians.

I came across this database on invasive species that published the 100 worst invasive species on the planet - from aquatic plant to mammals:

Click the link above for reference

 First of all, what are invasive species?

"Invasive species are plants or animals that do not belong where humans have intentionally or accidentally brought them. " - WWF

Humans, with or without intention, have introduced some of these species to places and have caused extinctions to some other species. 

I remember reading an article about crayfish last year, Thomas Breithaupt, an employee at the UK Environment Agency, found up to 20 signal crayfish per square metre in some areas. Humans introduced them from America for aquaculture purposes 30 years ago. What's important is that such concentration of the non-native species will lead to the 'outcompetion' of other species. In fact, humans spread invasive species in different ways, and the frequency has increased. For example, the rate of invasion into San Francisco Bay rose from one to three invader per year in 1961-1995. Invasive species found their route through foreign sources or across watershed boundaries. Over 400 species were introduce during the 1961 - 1995 compared to just 67 in 1850 - 1900.

Frequency of occurrence for vectors of introduction for alien invasive species that are threat facts for listed fish species in Canada

In Canada, most invasive species in freshwater were introduced due to sport fishing. In fact, 85% of the introductions that affected native species were intentional, while 88% of these were related to sport fishing. Although in general, over 75% of the species face not only threat from invasive species, such factor appeared to be the only contributor to the extinction of North American fish taxa. Invasive species were also considered to be the second greatest threat to imperilled species in America. Dextrase and Mandrak mapped the significance of invasive species, they affected more than half of the listed species in Canada. 

Number of listed fish species and the proportion that are threatened by alien invasive species in each freshwater ecological area in Canada (Height = number of listed species, solid = number of listed species threatened by invasive species)

Humans often introduce non-native species with good intention, but result in bad consequences, including the potential extinction of local species. Apart from Small Indian Mongoose and signal crayfish, zebra mussels were also deliberately introduced to some aquatic environments. They are famous for being efficient filter feeders that increase water clarity. However, the mussels bioaccumulate toxins that are harmful to native species like fishes and birds that consume them. 

Recently, there has been raised awareness of the harmful effect from invasive species, and has encouraged discussions upon solutions. National Wildlife Federation suggested three main focuses: 

1. Prevention of their introduction in the first place

2. Create monitoring systems for detecting new infestations

3. Move rapidly to eradicate newly detected invaders

These initiatives are relatively easy to come up with, but difficult to implement. Actual practices, such as biological control of invasive pests, were used in Hawaii. Yet, this method is controversial, as it caused extinction of some other non-target species. For instance, the introduction of 16% of 313 parasitoid species to eradicate holometabolous pests attacked other native species in North America.  

Facing non-native species, many species are outcompeted and have therefore gone extinct. On another note, human intervention in removing the invasive species they introduced is argued to cause further adverse impact on native species. Hopeless?

We can just anticipate that better solutions, which would not contribute further to extinction, will be put in effect soon. 

Humans, Freshwater, Species

Endangered Coahuilan box turtle in Mexico

Previously, I talked about habitat loss of species. Little do we know, freshwater is facing greater pressure from humans and extinction is fast approaching freshwater species..

"Massive mismanagement and growing human needs for water are causing freshwater ecosystems to collapse, making freshwater species the most threatened on Earth. Extinction rates for freshwater species including fish, frogs, crocodiles and turtles were four to six times higher than their terrestrial and marine cousins." - Diversitas, an international group of biodiversity experts 

It is not beyond imagination that human source of threats are not restricted within habitat loss. Dudgeon and his team suggested that impact posed by humans consist of five main categories:

Five major categories on freshwater biodiversity

The impact of human on freshwater is interrelated with their other influences, as demonstrated above. Pollution is one of the most serious problems. Water pollution from domestic and industrial sources leads to excessive nutrient enrichment and the growth of other chemicals like endocrine disrupters. This chemical will cause disturbance to the hormone systems of species. Hence, it leads to possible depletion of species. Habitat alterations such as forest clearance, as mentioned previously, can change the surrounding of the homeland of species. For instance, it will increase river sediment loads and lead to shoreline erosion. The disproportionate water distribution for plants and animals (Surface freshwater habitats contain only 0.01% of world's water but are housing 40% of global fish diversity and 25% of global vertebrate diversity), together with the other harmful effects brought by humans, make freshwater species highly vulnerable to extinction. 

Not convinced?

The edge of extinction is actually highly visible in many places, where a lot of freshwater species are now endangered due to disturbance from humans. In Spain, record of threatened freshwater fish can be dated back from 1986.  

Percentages of endangered freshwater fish in Spain
Ex?: Probably extinct, E: endangers, V: vulnerable, R: rare, I: indeterminate, K: insufficiently known, NT: not threatened 

Unthreatened species significantly decreased. In 1992, there was 1% of freshwater fish at the edge of extinction. Amount of rare species raised 7%, including Hucho hucho, Salelinus fontinalis and Ictalurus melas. 

Hucho hucho

Salvelinus fontinalis

Ictalurus melas

Human, not surprisingly have played a crucial role in effecting the endangered fish. Construction of 11, 000 large dams in Spanish rivers has jeopardised survival of migratory species. These dams also led to significant loss of habitat with establishments of large reservoirs, water-flow regulation and water withdrawal. 

Here's a quick summary: Freshwater habitat, contains the most endangered species. They are highly affected by human activity and modification to the surroundings. There were already 20% of freshwater species that had gone extinct. Given the limitation on research in vast freshwater species, it is likely that more than that are close to extinction. Have people thought about the consequences before building dams and clearing forests?

Habitat Fragmentation

Monday's blue - Yes, species have been losing their homeland!

In the previous blog, I mentioned how humans have been altering landscapes and hence have impacted livelihood of many species. Today, I would like to examine further into this area - extinction due to the loss of homeland. Without doubt, human developed at the expense of nature. Bennet and Saunders argued that the destruction and fragmentation of habitats are major factors in decline of populations of species. Southeast Asia had one of the highest loss of species in mammal population extensions: 57% of its quadrants have lost between 75-100% of their mammals.

First of all, habitat fragmentation is the dismantling of continuous habitat, such as tropical forest. resting in three phenomena. 

1. Habitat loss
2. Subdivision of the remaining vegetation - Habitat fragmentation
3. Replacement of vegetation 

Although the third situation might be favourable to species, the initial removal of large tracts of native vegetation would have already modified physical processes and the environment. Say, cleared land would have different humidity, ground and air temperature and wind speed compared to forests. Even with the replacement of vegetation, it is close to impossible to create a perfect resemblance of the previous habitat. In addition to the time gap until the replacements, species may evolve, migrate, or decline in populations. 

Lemuroid ringtail possum - also known as Lemur-like ringtail possum

Rainforest fragments are found in Queensland, Australia. A research found that with time lag, species richness in fragments declined further from 1986. As a result, by 2006-7, the lemuroid ringtail possum has become an endangered species.

Evidently, the loss of species in 2006 (open circles) was more serious compared to that of 1986 (filled circles). 

There are, however, some species that have higher tolerance for human disturbance, such as Spotted hyena. Despite this attribute, the population of Spotted hyena also lost 14%. 

Spotted hyena - also know as Laughing Hyena

Extinctions today concentrated either in areas of high human population densities, or places where human activities dominant. Southeast Asia is one of the examples - human population density is extremely high. Countries such as China and India are countries that have the  highest populations in the world. 

Southeast Asia
Left to right: Historic number of species with populations in each 2 x 2 quadrate,  number of species lost from each quadrate, percentage of species that have disappeared from each quadrate 

North America
Left to right: Historic number of species with populations in each 2 x 2 quadrate,  number of species lost from each quadrate, percentage of species that have disappeared from each quadrate 

Lost species concentrated within the categories of 5-6 and 7-8, where populations were high. Similarly, North America had the highest percentage losses in the heavily populated eastern United States. 

Summarising the above, as humans have been removing forests to build skyscrapers, species are forced to leave their homes. As they fail to adapt to new environments, extinction will be inevitable. The question will again be: What's next? Development is unstoppable, and there are little escape routes for species..